S Shrestha1, O Olén2,3, S Montgomery4,5,6, I Schoultz1, Å Hallqvist Everhov7,8, - The Swibreg Study Group9,10, P Myrelid9,10, J F Ludvigsson11,12,13,14, M Sachs15, J Halfvarson16

Validation of IBD diagnoses and Montreal Classification defined subgroups of the diseases in the Swedish National Patient Register

1School of Medical Sciences, Örebro University, Örebro, 2Unit for Clinical Epidemiology, Department of Medicine, Karolinska Institute, 3Sachsska barn- och ungdomssjukhuset, Department of Clinical epidemiology, Department of Medicine, Karolinska Institutet, Stockholm, Sweden, 4Clinical Epidemiology and Biostatistics, School ofMedical Sciences, Örebro University, Örebro, 5Clinical Epidemiology Division, Department of Medicine, Karolinska Institute, Stockholm, Sweden, 5Department of Epidemiology and Public Health, University College London, London, UK, 7Department of Clinical Science and Education, Södersjukhuset, Karolinska Institute, Stockholm,Sweden, 8Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden, 9Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden, 10Department of Surgery, Linköping University Hospital, Linköping, Sweden, 11Division of Epidemiology and Public Health, Schoolof Medicine, University of Nottingham, Nottingham, UK. 12Department of Medicine, Columbia University College of Physicians and Surgeons, New York, USA, 13Department of Medical Biostatistics and Epidemiology, Karolinska Institute, Stockholm, Sweden, 14Barn- och ungdomsmedicinska kliniken, Örebro universitetssjukhus, Örebro,15Unit for Clinical Epidemiology, Department of Medicine, Karolinska Institutet, Stockholm, Sweden, 16Department of Gastroenterology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.

BACKGROUNDThe Swedish National Patient Register (NPR) is an important data source for research and a previous study has shown a high validity for a diagnosis of inflammatory bowel disease (IBD) in cases registered both in the Swedish quality registry for IBD (SWIBREG) and the NPR. However, whether the information on International Classification of Diseases (ICD) codes from the NPR can be used to predict subgroups

of IBD is unknown.

§ Medical records of 1403 patients registered in SWIBREG were reviewed and classified according to international accepted criteria for subtype of IBD and according to the Montreal classification.

§ The first two IBD-associated ICD codes in the NPR, 1966-2014, were used to predict incident diagnoses.

§ NPR data during the 5 years preceding the review of medical records were used for prediction of prevalent IBD.

§ ICD diagnosis and procedure codes in the NPR were used to predict subgroups of patients according to the Montreal classification, as previously described*.

§ Positive predictive values (PPV) with 95% confidence interval were calculated.

METHODS AND MATERIALS

Based on the medical records, 854 patients were diagnosed with CD, 519 patients with UC and 30 with IBD-U (Table 1a). Information on PPV for predicting incident and prevalent cases of IBD type and its various subgroups is shown in Table 2.

Age at diagnosis were stratified to A1, A2 and A3 (A1≤16 years, A2:17-40 years, A3>40 years) for the ICD codes,

and PPV were calculated to be 95% (95%CI=93–98), 96% (95%CI=95–97) and 90% (95%CI=86–94) respectively.

RESULTS

CONCLUSIONSThe validity was high for age at diagnosis, for types of IBD among incident and prevalent cases and some subtypes. However, the validity was less impressive in other subtypes and it should be considered in the future studies.

Correspondance Author

jonas.halfvarson@regionorebrolan.se

Figure 1:http://tmedweb.tulane.edu/pharmwiki/doku.php/inflammatory_bowel_disease_ibd

Pred

icte

ddi

agno

sis

base

d on

NPR

Gold Standard-Medical record review

CD UC IBD-U TotalCD 536 0 5 541

UC 5 380 8 393

IBD-U 313 139 17 469

Total 854 519 30 1,403 Pred

icte

ddi

agno

sis

base

d on

NPR

Gold Standard-Medical record review

CD UC IBD-U TotalCD 783 35 11 829

UC 4 406 5 415

IBD-U 63 75 13 151

Total 850 516 29 1,395

Tables 1a and 1b: Frequency table for prediction of incident and prevalent cases in patients with IBD

PPV for IBD type among incident cases

PPV for IBD type among prevalent cases

CD: 99% (95%CI=98–100) CD: 94% (95%CI=93–96)

UC: 97% (95%CI=95–98) UC: 98% (95%CI=96–99)

IBD-U: 4% (95%CI=2-5) IBD-U: 9% (95%CI=4-13)

Table 2: Prediction of IBD and its subtypes among incident and prevalent cases

CD; Crohn’s disease, UC; ulcerative colitis, IBD; inflammatory bowel disease and IBD-U; inflammatory bowel disease unclassified.

PPV for subtypes of CD and UC among prevalent casesColonic location (L2): 37% (95%CI=33–41)Ileal (L1)/ileocolonic (L3)/ 81% (95%CI=77–86)unknown location (LX):

Perianal disease: 82% (95%CI=78–87)

Inflammatory disease (B1): 62% (95%CI=58–67)

Complicated disease (B2/B3): 76% (95%CI=72–81)

Proctitis (E1)/left-sided (E2): 78% (95%CI=69–88)

Extensive (E3): 83% (95%CI=78–87)

* Everhov ÅH et al. Gastroenterology. 2018;154:518-528

Figure 1:http://tmedweb.tulane.edu/pharmwiki/doku.php/inflammatory_bowel_disease_ibd