STUDY PROTOCOL Open Access

Protocol of a cluster randomized trial toinvestigate the impact of a type 2 diabetesrisk prediction model on change in physicalactivity in primary careEsther Jacobs1,2* , Miguel Tamayo3, Joachim Rosenbauer1,2, Matthias B. Schulze2,4, Oliver Kuss1,2,5

and Wolfgang Rathmann1,2

Abstract

Background: Little evidence exists on the impact of diabetes risk scores, e.g. on physicians and patient’s behavior,perceived risk of persons, shared-decision making and particularly on patient’s health. The aim of this study is toinvestigate the impact of a non-invasive type 2 diabetes risk prediction model in the primary health care setting ascomponent of routine health checks on change in physical activity.

Methods: Parallel group cluster randomized controlled trial including 30 primary care physicians (PCPs) and 300participants in the region of Düsseldorf and surrounding urban and rural municipalities, West Germany. On clusterlevel, PCPs will be randomized into intervention or control group using a biased coin minimization technique.Participants in the control group are going to have a routine health check “Check-up 35” which is recommendedbiannually for all people ≥35 years of age in Germany. In the intervention group, the routine health check isexpanded by usage of a non-invasive diabetes risk prediction model (German Diabetes Risk Score). Primaryoutcome is change in physical activity after 1 year. Secondary outcomes include aspects of targeted counseling,motivation of participant’s to change lifestyle, perceived and objectively measured diabetes risk, acceptance ofdiabetes risk scores, quality of life, depression and anxiety. Patients will be followed over 12 months. Hierarchical ormixed models will be conducted, including a random intercept to adjust for cluster, the respective baseline value,and covariates to compare the groups.

Discussion: This pragmatic cluster randomized controlled trial will enhance our knowledge on the clinical impactof diabetes risk scores for the first time in the real-life primary health care setting.

Trial registration: ClinicalTrials.gov NCT03234322, registered on July 28, 2017.

Keywords: Risk score, Prevention, Type 2 diabetes, Physical activity, Behavior, Cluster randomized controlled trial

BackgroundStudies on lifestyle interventions with participants of highrisk for type 2 diabetes have shown that modifiable riskfactors, such as physical inactivity and overweight can bereduced, thus, diabetes can be postponed or even

prevented [1, 2]. For practical implementation of suchprograms, the major challenge is the identification ofhigh-risk individuals. Primary care physicians (PCPs) arethe first point of contact for health-related issues and havecomprehensive knowledge about the medical condition ofthe person and his family, thus, they are the ideal contactpoint to identify persons at risk. Up to now, the screeningprocess differs between PCPs, meaning the selection ofpeople with increased diabetes risk is based on the individ-ual decision to combine different screening steps. Theseinclude an initial screening based on single risk factors

* Correspondence: esther.jacobs@ddz.uni-duesseldorf.de1Institute for Biometrics and Epidemiology, German Diabetes Center (DDZ),Leibniz Center for Diabetes Research at Heinrich Heine University Düsseldorf,Auf’m Hennekamp 65, 40225 Düsseldorf, Germany2German Center for Diabetes Research (DZD), 85764 München-Neuherberg,GermanyFull list of author information is available at the end of the article

© The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Jacobs et al. BMC Endocrine Disorders (2018) 18:72 https://doi.org/10.1186/s12902-018-0299-2

(e.g. age, weight, sex, Body-Mass-Index (BMI)) or diabetesrisk scores including multiple risk factors as well as themeasurement of blood glucose (fasting plasma glucosetest, oral glucose tolerance test (OGTT), hemoglobin A1ctest (HbA1c)) to determine the diabetes risk and glucosemetabolic disorders [3].Diabetes risk scores are predictive models to estimate

the probability for an individual to develop diabetes withina defined time period. Those scores without laboratorymeasures (non-invasive risk scores) are more suitable forapplication at the population level, since they mostly in-clude simple questions regarding anthropometric and life-style factors [4]. It has been proposed that using diabetesrisk scores as first step of diabetes screening is more prac-tical than blood glucose tests, as the latter are time con-suming and costly [5]. Hence, the interest in thedevelopment of diabetes risk scores is still unabated. Inthe last years, several hundred diabetes risk predictionmodels were developed worldwide [6, 7]. However, littleevidence exist on the impact of diabetes risk scores, i.e. onphysicians and patient’s behavior, perceived risk of per-sons, shared-decision making in order to make an in-formed decision and particularly patient health [5, 7]. Todate, only one study by Godino et al. [8] has been pub-lished, which assessed the effect of communicating an es-timate of genetic or phenotypic risk of type 2 diabetes onphysical activity. In this study, several modes of communi-cation were used to inform the participants about their in-dividual risk, including face-to-face counseling, telephoneconversations, and printed materials [9]. However, uncer-tainty still exist on the impact of diabetes risk scores inthe primary health care setting.

AimGiven the rapid development of diabetes risk scores and asimultaneous reluctance of PCPs to implement diabetesrisk scores in everyday practice [10], there is an urgentneed to expand our knowledge of the impact of diabetesrisk scores in the primary health care setting. Thus, theaim of the study is to investigate the impact of anon-invasive risk prediction model in the primary healthcare setting as component of routine health checks. Toprevent contamination effects between participants andalso possible dilution effects of PCPs counseling strategy,the study is designed as cluster randomized trial, thus,PCPs will be objects of randomization.

ObjectivesOur primary objective is to investigate whether the ap-plication of the diabetes risk prediction model on indi-vidual level including an oral explanation of the result inthe physician-patient consultation as component of theroutine health checks in primary care will improve phys-ical activity of individuals 1 year after the routine health

check. Our secondary objectives are to determine, if theintervention will improve the counseling process regard-ing preventive strategies on balanced nutrition, bodyweight reduction and smoking secession, lead to im-proved shared decision making, and increase the motiv-ation to change lifestyle. Furthermore, the aims are toevaluate whether the risk score leads to changes in BodyMass Index (BMI), quality of life, level of depression andanxiety, the perceived risk of developing diabetes as wellas change on the individual diabetes risk. A final goal ishow the application of a diabetes risk prediction modelwill be accepted as instrument for routine use in clinicalpractice.

Methods/designStudy designThe study is a pragmatic blinded parallel group superioritycluster randomized controlled trial. Clusters are PCPs(general practitioners, medical practitioners and internistsworking as general practitioners) located in the region ofDüsseldorf and surrounding urban and rural municipal-ities in the federal state of North Rhine-Westphalia inGermany. They will be randomized to intervention orcontrol group by minimization technique with a 1:1 allo-cation ratio [11].

Recruitment of PCPs and participantsPCPs will be invited by the Association of StatutoryHealth Insurance Physicians North Rhine and the Ger-man Diabetes Center in Düsseldorf, both located inNorth Rhine-Westphalia, Germany. All PCPs with andwithout further training in diabetology according to Ger-man Diabetes Association standards that provide theroutine health check can participate in the study, exceptPCPs who treat exclusively patients with private insur-ance or diabetes patients only. On invitation, all PCPswill receive an information letter including all aspects ofthe study with a consent form and baseline questionsneeded for randomization. Those interested to partici-pate will send their consent and the answers to the base-line questions to the study center at the GermanDiabetes Center. All PCPs willing to participate will beconsecutively randomized into one of the study groupsuntil the target of 30 PCPs is achieved.Thereafter, the PCPs will start to recruit ten people

within a maximum of 2 years. To prevent selection bias,PCPs are constrained to recruit consecutively peoplewho fulfil the following inclusion criteria: Appointmentfor the routine health check, statutory health insurance,age of > 35 years, and a BMI of ≥27 kg/m2. People arenot eligible if they have been diagnosed with type 1 ortype 2 diabetes or had already at least one measurementof abnormal blood glucose level (fasting glucose≥126 mg/dl or 2 h oral glucose tolerance test (oGTT) ≥

Jacobs et al. BMC Endocrine Disorders (2018) 18:72 Page 2 of 13

200 mg/dl or glycated hemoglobin (HbA1c) ≥6,5%) be-fore the routine health check. Further exclusion criteriaare no sufficient German language skills to fill out thequestionnaires, presence of an incurable disease with aprognosis of less than 1 year, severe mental illness or de-mentia, and a severe underlying disease, which largelyimpairs physical activity. Further excluded will be preg-nant women and people who participated in anotherclinical study 30 days before study inclusion.

InterventionThe intervention will be integrated into a routine healthcheck (Check-up 35), which all people in Germany withstatutory health insurance > 35 years are entitled toevery 2 years. The routine health check (Check-up 35) isconducted on two separate days and will be extendedonly with questionnaires in both groups, meaning thatno study-specific additional measurements will be taken.On the first day of the Check-up 35, the medical his-

tory is obtained and medical examination (completephysical examination and laboratory tests of blood andurine) is carried out. On the second day of the healthcheck, which is usually a few days after the first day, aconsultation takes place in which the results of thehealth check and preventive opportunities are discussed.In the actual study, all people entering the PCP prac-

tice with an appointment of a routine health check andfulfilling the inclusion criteria will be informed about thestudy and receive an information letter including theconsent form on the first day. They will enter the studywhen they give informed consent. On the second day ofthe routine health check, participants of both groups willreceive the baseline questionnaire that can be filled induring waiting time. This questionnaire contains, amongothers, sociodemographic information, contact details,and questions on lifestyle, including physical activity aswell as on quality of life.The participants having an appointment for a routine

health check by a PCP who is assigned to the interven-tion group will receive the risk prediction model “TheGerman Diabetes Risk Score” (GDRS) in addition to thebaseline questionnaire.The GDRS is based on a prospective cohort study

(European Prospective Investigation into Cancer and Nu-trition [EPIC]-Potsdam study), including 25,000 peopleand has been externally validated several times [4, 12–14].It was shown that the GDRS provides good prediction oftype 2 diabetes incidence according to the receiver operat-ing characteristic curve (ROC-AUC): [95%-KI]: 0.86[0.84–0.87]) [13], even in other German cohorts (ROC-AUC between 0.70–0.87) [12, 14]. The GDRS focuses onmodifiable non-invasive risk factors and consists of elevenquestions on age, height, waist circumference, hyperten-sion, physical activity, smoking status, intake of whole-

grain bread, intake of red meat, coffee consumption, andtwo questions regarding the family history of diabetes(parents and siblings) to predict the five-year diabetes risk.In addition, the GDRS contains a visual presentation ofthe individual diabetes risk and short recommendations toenhance healthy lifestyle. The filled diabetes risk score willbe used in the counseling interview with the PCP at theend of the health check as a practical guide to discuss in-dividual tailored preventive strategies.

ControlAll participants having an appointment for a routinehealth check by a PCP who is allocated to the controlgroup will receive solely the routine health check and fillout the regular baseline questionnaire.

Further study courseAfter the health check, participants will be followed for12 months. They receive questionnaires after six and 12months which can be filled in online by using a person-alized link or otherwise paper based. The questionnairesinclude, among others, questions about their lifestyle,current status of health and the counseling session atthe end of the routine health check. Differences betweenthe questionnaires in the two groups are related to theuse of a diabetes risk score in the intervention group.Anthropometric measures of participants are object-

ively measured by PCPs at the first day of the healthcheck at baseline and via self-report at follow-up assess-ments. As the waist circumference is overestimated bypatients without initial guidance by the PCP (in averageabout 6 cm) [15], patients will be trained at the baselineappointment in order to ensure accurate measurement.After the baseline medical appointment, participantstake the measuring tape for the follow-up questionnairesat six and 12 months. Laboratory tests (blood and urine)will be performed at baseline and updated in case of an-other doctor’s visit in the follow-up within a maximumtime frame of 3 years.In addition to the measurements taken from the par-

ticipants, measurements will also be taken from thePCPs, e.g., on PCP’s workflow in the medical office, im-plementation of lifestyle prevention strategies, and ac-ceptance of the application of a diabetes risk score in theprimary health care setting. PCPs will receive two gen-eral questionnaires at baseline and after inclusion of thetarget number of participants. Furthermore, one ques-tionnaire is filled in by the PCP after each health checkwith a study participant. This questionnaire includesquestions about the content of consultation at the endof the routine health check, shared decision making, aswell as obtained clinical data. At least 1 year after inclu-sion of all participants, clinical data of each participantwill be updated by the PCPs.

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Figure 1 shows the flow diagram of the study. Table 1gives an overview on participant’s self-reported mea-sures, Table 2 lists measures assessed by PCPs. Thequestionnaires, which are compilations of validatedquestionnaires, and adopted questions from previousstudies or systematic reviews, were developed and testedby an interdisciplinary team, and were validated usingcognitive interviewing techniques with a sample of sixPCPs and six persons. Furthermore, questionnaires anddata collection process were tested in a pilot study wasconducted including four physicians and 33 participants.To ensure adherence to the protocol, the study

personnel will arrange a face-to-face meeting with eachPCP at the beginning of the trial. At the meeting, all as-pects of the study are discussed, including the recruit-ment of participants, handling of the questionnaires andconduct of the health check with or without the

application of the risk prediction model. In addition, avideo explaining all aspects of the study will ensure ad-herence to the protocol during the time of the study.

Primary outcome measure

� Difference in physical activity at 12 months after theroutine health check between the groups.

We will assess physical activity with the internationallyvalidated questionnaire International Physical ActivityQuestionnaire Short Last 7 Days Format (IPAQ-SF),which has been shown to be a reliable and valid tool toobtain comparable estimates of physical activity [16]. Thequestionnaire includes questions on different levels ofphysical activity (walking, moderate- and vigorous-inten-sity activities), their frequency (days per week in the last 7

Fig. 1: Flow diagram of the study

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Table 1 Self-reported measures assessed by participants

Measures Brief Description Time of assessment

Baseline(Check-up 35visit)

Follow-up6 months

Follow-up12 months

Sociodemographic andanthropometric characteristicsc

Age, sex, height, first language,family status, level of education,employment status

✓ IG, CG

Weight, smoking status,presence of hypertension

✓ IG, CG ✓ IG, CG ✓ IG, CG

Neighborhood environmentalperception and dog ownershipc

Physical activity is correlated withseveral environmental factors,thus we use the first sevenquestions of the validated Europeanquestionnaire “ALPHA” [30]to assess environmental perceptions.For the same reason,we included a question about dogownership derivedfrom another study byPanter et al. [31].

✓ IG, CG

Social residential environmentc Physical activity is correlatedwith assistance from familyand friends, thus, fourquestions are included,rated on a 4-point Likertscale (completely agree -completely disagree)adopted from another studyon physical activity andresidential environment [32].

✓ IG, CG

Physical activitya International Physical ActivityQuestionnaire (IPAQ)-Short Form [16],intentionally mostly used validatedquestionnaire to assess physical activityof the last seven days.The questionnaire consists ofseven questions and has acceptablemeasurement properties [16].

✓ IG, CG ✓ IG, CG ✓ IG, CG

Counselingprocessb

counselingcontent

Questions about the content ofconsultation regarding the lifestylefactors weight reduction, changeof diet, physical activity andsmoking cessation.Discussion of lifestyle factors,target agreements, receivedinformation, referral toexperts/counseling centers.Questions were obtained from astudy on diabetes screening byHussain et al. [33]

✓ IG, CG

future medicalappointments

Question, if a medical appointmentwas arranged and observed.This aspect was identified inan earlier focus group with PCPs inthe planning phase of the trial.

✓ IG, CG

Proportion of shared decisionmakingb

Modified questionnaire to assessshared decision making for diabetesprevention opportunities includingsix questions. Five questions areranked on a 6-point Likert scale(completely disagree-completely agree),and one overall question.The original questionnaire PEF-FB-9 [34]was developed and validated forclinical encounters in the primary

✓ IG, CG

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Table 1 Self-reported measures assessed by participants (Continued)

Measures Brief Description Time of assessment

Baseline(Check-up 35visit)

Follow-up6 months

Follow-up12 months

health care setting and people withan existing medical decision.

Motivation and/ or change oflifestyleb

For assessment of readiness tochange lifestyle (weightreduction, regularphysical activity,healthy diet, smokingcessation) we usethe stage of changemodel developed byProchaska et al. [35–38],allowing allocation ofindividuals to differentstages of readinessfor change (fromprecontemplation throughcontemplation, preparation,and action to maintenance)

✓ IG, CG ✓ IG, CG ✓ IG, CG

Changes of medicalconditionb

General medicalcondition

Self-rated overall health questionwith five answer alternatives“very good”, “good”, “fair”,“bad”, “very bad” suggested byWorld Health Organizationand already used in anational representativeGerman study (DEGS1) [39, 40]

✓ IG, CG ✓ IG, CG ✓ IG, CG

Depression andanxiety

The Hospital Anxiety andDepression Scale (HADS)is a validated questionnaireto assess anxiety anddepression. The questionnaireconsists of 14 items, sevenanxiety and seven depressionitems and showed good reliabilityand validity in several settingsincluding general population [41, 42].

✓ IG, CG ✓ IG, CG ✓ IG, CG

Changes in diabetes riskb Changes of diabetes risk in theintervention groupwill be analyzed, as wellas differences betweenthe groups atfollow-up. The German DiabetesRisk Score [13]is a validated non-invasiverisk score to predict the five year riskof developing diabetes. It consists ofeleven questions with modifiable(dietary habits, physical activity)and non-modifiablefactors(e.g. age, height, family history ofdiabetes). Only the interventiongroup receives the originalquestionnaire at baseline.In the follow-upthe questions of the risk scoreare included separatelywithout any risk outputin both groups.

✓ IG ✓ IG, CG ✓ IG, CG

Perceiveddiabetes riskb

Memory ofdiabetes risk

Participants are asked, if theycan remember in which riskcategory they were assigned

✓ IG ✓ IG

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days) and duration (minutes per day, at least 10 minutesof activity). In our study, physical activity will be measuredat baseline, and at six and 12 months follow-up. Low,moderate, and vigorous physical activity will be calculatedas the sum of the metabolic equivalent of task (MET) mi-nutes per week, according to the standard official manual[17], in which all minutes of activity during the last 7 daysare multiplied with the respective metabolic rate which isdefined as 3.3 for walking, 4.0 for moderate physical activ-ity and 8.0 for vigorous physical activity. This primary out-come measure was selected as it is a patient relevantoutcome that reflects possible lifestyle changes, startingwith the application of the diabetes risk score in the coun-selling interview of the routine health check. This can im-prove awareness of participants regarding risk factorsassociated with diabetes, which may lead to a healthierlifestyle.

Secondary outcome measures

� Improvement in the counseling process regardingpreventive strategies on balanced nutrition, bodyweight reduction and smoking secession,

� improvement of shared decision making,� change in BMI� improved motivation to change lifestyle,� change in quality of life, and change in level of

depression and anxiety,

� change of the perceived risk of developing diabetes,� acceptance of the application of a diabetes risk score

for routine use in clinical practice.

Other Pre-specified Outcome Measures

� Change in individual diabetes risk at 6 and12 months in the intervention group and differenceof individual diabetes risk between 6 and 12 monthsfollow-up between the groups.

All secondary and other outcome measures will be ob-tained via self-report questionnaires. Detailed informa-tion of the measures and time points of assessment canbe found in Tables 1 and 2.

Sample sizeThe primary endpoint will be the change in physical ac-tivity after 12 months follow-up between the groups,measured by the IPAQ short form questionnaire as thesum of MET minutes per week [16, 17]. The study byYates et al. [18] had a comparable study design, hence,we use this study as the reference for sample size esti-mation. In the Yates study, participants had an inter-quartile range of 1180–4719 MET minutes per week,which corresponds approximately to a standard devi-ation of 2665 MET minutes per week [19]. Our pilotstudy conducted prior to the main study showed similar

Table 1 Self-reported measures assessed by participants (Continued)Measures Brief Description Time of assessment

Baseline(Check-up 35visit)

Follow-up6 months

Follow-up12 months

by the German Diabetes RiskScore at baseline. This questionreflects the perceivedimportance of diabetes riskand intensity of awareness.The question is adoptedby a study from Godino et al. [9].

Perceiveddiabetes risk

Questions about the perceivedrisk of already having type2 diabetes and perceivedrisk of developing type 2diabetes in the next fiveyears are included.The questions havebeen already used inother studies [9, 43, 44].

✓ IG, CG ✓ IG, CG

Acceptance of diabetesrisk scoreb

Different questionsregarding the understandability, length,and acceptance of the GermanDiabetes Risk Score. Questionswere adapted from other studies,aspects synthesized byDhippayom et al. [5]

✓ IG

CG control group, IG intervention group, PCPs primary care physicians, aprimary outcome, bsecondary outcome/other outcomes, cgeneralmeasures/confounder measures

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Table 2 Measures assessed by PCPs

Measures Brief Description Time of assessment

Baseline at inclusion For eachparticipant

Follow-upafterrecruitingcompleted

One yearafterinclusion ofall participants

Demographic statistics andinformation about PCP andmedical officec

Sex, age, date of establishment, medicaldegree, additional degrees, type of medicaloffice (community practice, solo practice etc.)

✓ IG, CG

Number of patient contacts and healthchecks (Check-up 35) per quarter

✓ IG, CG ✓ IG, CG

Counselingprocessb

Motivation andimplementation ofprevention strategiesin general

We use a set of questions from the validatednationwide survey on modifying healthbehavior to prevent cardiovascular diseasesamong German PCPs (ÄSP-Study) [45]:a) Frequency of provision of lifestyle adviceof weight reduction, increasing physical activity,achieving a healthy diet, quitting smoking,and some further measures of risk factorson a 5-point Likert scale (no provision -provision to all patients)b) perceived importance of reductionof risk factors is rated on a 4-pointLikert scale (very important - notimportant at all)c) PCPs self-rated competence tomotivate patients changing lifestyle isalso rated on a 4-point Likert scale(very high - very low)d) The level of PCPs’ agreement tostatements regarding attitudes,self-competence, and self-efficacyof PCPs is rated on a 4-point Likertscale (completely agree -completely disagree)e) Cooperation’s to otherinstitutions and experts regardingpreventionIn addition, questions on obstaclesof counseling were derived fromtwo qualitative studies on lifestylecounseling in diabetes care andobese patients [46, 47]

✓ IG, CG ✓ IG, CG(solely aand c)

Content ofcounseling withparticipant

After each routine health check witha study participant PCPs are askedabout the content of counseling(counseling, information material,and referral to expert) regardingweight reduction, increasing physicalactivity, achieving a healthy dietand quitting smoking usingtick boxes. The framework isadopted from two studies [45, 48].

✓ IG, CG

Future medicalappointments

Question, if a medical appointmentwas arranged and when. This aspectwas identified in an earlier focusgroup with PCPs in the planningphase of the trial.

✓ IG, CG

Proportion of shared decisionmakingb

Modified questionnaire to assessshared decision making fordiabetes prevention opportunitiesincluding six questions. Five questionsare ranked on a 6-point Likert scale(completely disagree-completely agree),and one overall question. Theoriginal questionnaire PEF-FB-doc [49]is the pendant to PEF-FB-9 and was

✓ IG, CG

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results on the standard deviation of physical activityafter 3 months. The study by Yates et al. yielded an ob-served group difference of 2836 MET minutes per week,however, with a more intensive program. Thus we setour minimally clinically relevant effect to 1050 MET mi-nutes per week including all types of activities, whichcorresponds to a group difference of moderate activityfive times a week for 30 min and walking for three timesa week for 45 min. As intracluster correlation coeffi-cients (ICCs) in cluster randomized trials in primarycare were observed to be small, we assume an ICC of0.01 [20]. Together with a projected cluster size of tenparticipants per cluster, this leads to a design effect of1.09 [21]. Finally, to detect a difference of 1050 MET mi-nutes per week with a standard deviance of 2665 MET, adesign effect of 1.09, an expected dropout rate of 30%, apower of 80%, and a significance level of 5% of acluster-adjusted t-test, 300 participants, split up on 15PCPs per study group are needed.

Recruitment strategyTo ensure adequate participant enrollment, the studyteam will maintain close contact to the PCPs. This in-cludes communication per email or telephone and the

collection of the baseline questionnaires at the PCP’spractices regularly. Hereby, the study personnel cansolve possible failures in the study process and resolvemissing values in the questionnaires promptly on-site.

Randomization, allocation concealment and blindingTo avoid dilution of the intervention effect, e.g. by par-ticipants exchanging information in the waiting room,the study was designed as a cluster trial, in which thePCPs are the unit of randomization. PCPs who are will-ing to participate are randomly allocated to interventionor control group by a blinded clinical data managerwithout knowledge of the PCPs. Minimization techniqueincluding biased coin design (p = 0,7) (Software: Mini-mPy 0.3 [22]) will be used to balance among the follow-ing properties of PCPs: residency (general medical vs.internal medicine), additional training in diabetology(yes or no) and the socio-economic environment of thepractices, based on statistical data about unemploymentrates in the defined region. It is not possible to blindPCPs according to study group, because of PCP net-works and knowledge exchange. In addition, it is notpossible to blind the researchers involved in the projectmanagement and implementation of the study, but

Table 2 Measures assessed by PCPs (Continued)

Measures Brief Description Time of assessment

Baseline at inclusion For eachparticipant

Follow-upafterrecruitingcompleted

One yearafterinclusion ofall participants

developed and validated for clinical encountersin the primary health care setting and peoplewith an existing medical decision.

Acceptanceof diabetesrisk scoreb

Use of diabetes riskscores

Question adopted from the ÄSP-Study [45]about which diabetes risk scores are knownand used in everyday practice.

✓ IG, CG

Attitude towardsdiabetes risk scores

Different questions regarding the usefulness,validity, understandability and acceptancetowards the diabetes risk score. Questionswere adapted from a qualitative study byMüller-Riemenschneider et al. [10] and asystematic review by Dhippayom et al. [5].Usefulness is rated on a 5-point Likert scale(not useful – very useful), all other questionsare rated on a 4-point Likert scale(completely agree - completely disagree)

✓ IG(CG: question aboutusefulness only if PCPknows diabetes riskscores)

✓ IG, CG

Anthropometric characteristics ofparticipantsb

The PCP measures waist circumference, weight,and height from each participant objectively.In the IG, measures are used to generatediabetes risk score.

✓ IG, CG

Clinical data from routine healthcheck (Check-up 35)c

Routine health check results (medicalexamination, lab tests, diagnoses) are collected,the questions are derived from a study thatwas conducted in the same health setting(Esther-Study) [48]. At the last survey,prescription of diabetes medication is asked inaddition.

✓ IG, CG ✓ IG, CG

CG control group, IG intervention group, PCPs primary care physicians, aprimary outcome, bsecondary outcome, cgeneral measures/confounder measures

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participants and researchers involved in the analysis willbe unaware of the assigned study group.

Data management, quality assurance and data protectionAll participants’ questionnaires filled in at baseline and allPCP questionnaires are paper-based and will be collectedin a study folder at the medical practice. A continuousmonitoring is performed by the study personnel, in whichthe questionnaires are checked for completeness andplausibility at the medical practice every quarter. Follow-up questionnaires for participants are sent and completedvia the online tool REDCap [23], a secure web applicationfor building and managing online surveys and databases,and otherwise by postal service. In case of missing or im-plausible values in the questionnaires, PCPs and partici-pants are contacted up to three times for completion orcorrection. Each PCP and participant receives a uniquenumeric identifier when participating in the study. Per-sonal information will be stored separately in locked filingcabinets, and the link between personal information andobtained data is only accessible by the study coordinator.All paper-based data will be doubly entered by trainedpersonnel to assure high data quality. Personal contact toPCPs and participants shall prevent premature drop-out.Furthermore, monetary incentives are given to PCPs andparticipants. All data obtained in the study are subject tostrict data protection regulations.

Data analysis and dissemination of resultsTo prevent systematic bias, analysis will be conductedusing the intention-to-treat principle. Missing values willbe handled by multiple imputation. For the purpose ofpossible bias due to the imputation of missing values,the analyses will also be conducted as complete caseanalysis and differences of both approaches will be dis-cussed (sensitivity analysis) [24]. For the analysis of theintervention effect (primary outcome at 12 months, sec-ondary outcomes at different time points) hierarchical ormixed models will be applied for primary and secondaryendpoints, including a random intercept to adjust forthe cluster effect, the respective baseline value, covari-ates used for minimization and individual covariates age,sex and smoking status of participants at baseline. Wewill use generalized linear mixed models with the iden-tity link for continuous and the logit link for binaryoutcomes.In terms of the primary endpoint, we define a differ-

ence of Δ = ± 300 MET / min per week or smaller as aclinically irrelevant difference. That is, if we observe the95% confidence interval for the primary endpoint lyingcompletely within [− 300; 300], we judge the interven-tion to be ineffective. The study will be reported accord-ing to the CONSORT statement for the reporting ofcluster randomized control trials [25].

EthicsThis study gained full ethical approval from the ethicscommittee of the Heinrich Heine University Düsseldorfin June 2017 (Reference-No: 5540).

DiscussionThis pragmatic cluster randomized controlled trial willenhance our knowledge on the impact of diabetes riskscores under real-life conditions in the primary healthcare setting. Especially non-invasive risk predictionmodels without laboratory measurements are free ofcharge and easy to apply, as the participants can answerthe questions themselves to obtain their personal risk ofdiabetes within the next years, thus, these questionnaireshave the potential to increase efficiency of identifyingpersons at risk. So far, a number of risk predictionmodels are ready to use and the utilization is required incurrent guidelines [3, 5, 7]. Unfortunately, PCPs use dia-betes risk prediction models only marginally because ofvarious barriers, e.g. lack of time and reimbursement, aswell as patient’s cultural or language issues [5, 10].A currently published randomized clinical trial by God-

ino et al. [8, 9] on effects of communicating the risk oftype 2 diabetes was the first controlled study examiningeffects of the application of a genetic or phenotypic riskscore compared to standard lifestyle advice on the healthbehaviors of participants recruited from the Fenland Study(UK). The study showed no significant intervention effectson physical activity and self-reported diet, weight, worryand anxiety. Solely the perceived risk was more accuratein those participants that received information about theirrisk estimate. Some factors need to be taken into accountwhen interpreting these results: study participants wererecruited from the Fenland study, which is a cohort ofrelatively young and slightly overweight individuals beforethe onset of chronic diseases [8, 26]. Furthermore, it is un-clear if possible dilution effects appeared in the counsel-ling effects, because Godino et al. did not declare ifmembers of the study team delivered the interventionsseparately. Finally, participants were not blinded to theintervention they received, meaning that participants inthe control group might have used phenotypic risk scoresavailable on the internet to obtain their personal riskestimate.However, there are also some limitations in our study

design. We use only self-reported measurements to assesslifestyle changes, e.g. physical activity. It is well known thatthe IPAQ somewhat overestimates physical activity [27],but other budget-friendly objective measurements, for ex-ample pedometer, measures only the distance travelled byfeet and often fail to record slower, shuffling steps, whichis often the case in older patients [28]. Moreover, objectivemeasurements with pedometers or accelerometers maymotivate patients to increase physical activity [29], an

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aspect, which could also lead to a dilution of the interven-tion effect in our study. The IPAQ is cost-effective, can as-sess discrete categories of physical activity, and is the mostused questionnaire to measure physical activity worldwide.Therefore, the results are comparable to other studies inthis field. Because we are interested in intraindividualchange of physical activity 6 and 12 months after the rou-tine health check, we believe the use of a self-reported in-strument in our study is acceptable. Another potentiallimitation is that the questions of the GDRS are also filledin by patients themselves. This could lead to an underesti-mation of diabetes risk [4]. However, all questions of theGDRS are short and easy answerable. All participants willbe trained on measurement of the waist circumference atthe day of routine health check and receive correspondinginstructions for all measurements they need to fill in thequestionnaire. In addition, a number of validation studiesshowed that the GDRS predicted insulin resistance withacceptable accuracy (ROC-AUC between 0.70–0.87) [4,12, 14], thus, we are convinced that the individual diabetesrisk can be measured adequately by the GDRS. Althoughparticipants are blinded concerning the intervention, incannot be excluded that people in the control group mayuse a diabetes risk score which are accessible for public onthe internet. However, this would only lead to an under-estimation of the intervention effect.Our study, which is designed as a blinded pragmatic

cluster randomized trial, will be conducted in close co-operation with PCPs to assess possible intervention ef-fects of the application of a risk prediction model in areal world setting without possible dilution effects in thecounselling process. Moreover, PCPs are the first pointof contact in which the relationship between the PCPand the participant is almost always characterized bytrust. The study participants will have a higher risk todevelop diabetes, based on the inclusion criterion BMI≥27 kg/m2. Besides that, we will pursue a pragmatic ap-proach that will lead to more heterogenic groups, espe-cially regarding age and medical condition. Anotherimportant aspect is that we are not only interested inmeasurements from the participants, but also from thePCPs. This will enable us to identify the habits, possiblechanges in the counseling process and the acceptance ofthe application of diabetes risk prediction models. Insummary, our study is slightly different to the study byGodino et al. [8] with a more pragmatic approach andadditional assessments of outcomes assessed by PCPsthat may have an impact on the outcomes in this trial.The application of diabetes risk prediction models may

lead to more targeted counseling on preventive opportunities, increase risk-awareness, and activates people’smotivation to change lifestyle. From the public healthperspective, the study results can contribute to futuredevelopment of diabetes prevention strategies, meaning

that in case of positive effects, diabetes risk predictionmodels could be regularly integrated in PCPs every daypractice. Overall, this easy applicable, low cost interven-tion may lead to cost reductions for the health caresystem.

AbbreviationsBMI: Body Mass Index; GDRS: German Diabetes Risk Score; HbA1c: Glycatedhemoglobin A1c; ICC: Intracluster correlation coefficient; IPAQ-SF: International Physical Activity Questionnaire Short Last 7 Days Format;MET: Metabolic equivalent of task; oGTT: Oral glucose tolerance test;PCPs: Primary care physicians; ROC-AUC: Receiver operating characteristicarea under the curve

AcknowledgementsWe thank all physicians and participants who contributed to the studypreparations. These included validation of questionnaires in qualitativeinterviews and conduct of a pilot study including four primary carephysicians and 33 participants.

FundingThis study is funded by a grant from the German Federal Ministry ofEducation and Research (BMBF) to the German Center for Diabetes Research(DZD). The German Diabetes Center is funded by the German FederalMinistry of Health and the Ministry of Innovation, Science and Research ofthe State of North Rhine-Westphalia.

Availability of data and materialsNot applicable

Authors’ contributionsAll authors gave important intellectual contributions, reviewed themanuscript and gave final consent to the version to be published. W.R.initiated and planned the study and reviewed the manuscript. E.J. plannedthe study design, is responsible for study management, and wrote the studyprotocol. M.T. contributed to the discussion, takes part in recruitment ofPCPs, reviewed the manuscript. J.R. contributed to the discussion, isresponsible for data safety, reviewed the manuscript. M.S. contributed to thediscussion, reviewed the manuscript. O.K. contributed to the discussion andto the design of the study, is responsible for the statistical analysis, andreviewed the manuscript. All authors read and approved the finalmanuscript.

Ethics approval and consent to participateThis study gained full ethical approval from the ethics committee of theHeinrich Heine University Düsseldorf in June 2017 (Reference-No: 5540).

Consent for publicationNot applicable

Competing interestsDr. Rathmann reported having received consulting fees for attendingeducational sessions or advisory boards from AstraZeneca, BoehringerIngelheim and NovoNordisk and institutional research grants fromAstraZeneca and NovoNordisk. No other potential conflicts of interestrelevant to this article were reported.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.

Author details1Institute for Biometrics and Epidemiology, German Diabetes Center (DDZ),Leibniz Center for Diabetes Research at Heinrich Heine University Düsseldorf,Auf’m Hennekamp 65, 40225 Düsseldorf, Germany. 2German Center forDiabetes Research (DZD), 85764 München-Neuherberg, Germany. 3TheAssociation of Statutory Health Insurance Physicians North Rhine,Tersteegenstraße 9, 40474 Düsseldorf, Germany. 4German Institute of HumanNutrition Potsdam-Rehbruecke (DIfE), Arthur-Scheunert-Allee 114-116, 14558

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Nuthetal, Germany. 5Institute of Medical Statistics, Düsseldorf UniversityHospital and Medical Faculty, Heinrich Heine University Düsseldorf,Düsseldorf, Germany.

Received: 14 September 2017 Accepted: 2 October 2018

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