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Supportive Care in Cancer ISSN 0941-4355 Support Care CancerDOI 10.1007/s00520-013-1978-1

Diagnostic accuracy of lipopolysaccharide-binding protein for predicting bacteremia/clinical sepsis in children with febrileneutropenia: comparison withinterleukin-6, procalcitonin, and C-reactiveproteinLidija Kitanovski, Janez Jazbec, SergejHojker & Metka Derganc

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ORIGINAL ARTICLE

Diagnostic accuracy of lipopolysaccharide-binding proteinfor predicting bacteremia/clinical sepsis in children with febrileneutropenia: comparison with interleukin-6, procalcitonin,and C-reactive protein

Lidija Kitanovski & Janez Jazbec & Sergej Hojker &

Metka Derganc

Received: 19 December 2012 /Accepted: 11 September 2013# Springer-Verlag Berlin Heidelberg 2013

AbstractPurpose In febrile neutropenia (FN), no reliable marker hasbeen identified to discriminate between severe infection andother causes of fever early in the clinical course. Sincelipopolysaccharide-binding protein (LBP) has proven to bean accurate biomarker of bacteremia/clinical sepsis in critical-ly ill non-immunocompromised infants and children, weperformed a prospective study to determine the diagnosticaccuracy of LBP in children with FN.Methods Concentrations of LBP, procalcitonin (PCT),interleukin-6 (IL-6), and C-reactive protein (CRP) were pro-spectively measured on two consecutive days in 90 FN epi-sodes experienced by 47 children. Receiver operating charac-teristic curve analysis was performed for each biomarker topredict bacteremia/clinical sepsis and severe sepsis.Results Eighteen of the 90 episodes were classified asbacteremia/clinical sepsis. On both days 1 and 2, all bio-markers had a low to intermediate diagnostic accuracy forsepsis, and no significant differences were found betweenthem (area under the curve (AUC) for LBP, 0.648 and0.714; for PCT, 0.665 and 0.744; for IL-6, 0.775 and 0.775;and for CRP, 0.695 and 0.828). Comparison of their AUCs tothe AUC of maximum body temperature on admission(AUC=0.668) also failed to show any significant differences.

In severe sepsis, however, the best diagnostic accuracies werefound for IL-6 and PCT (AUC 0.892 and 0.752, respectively),and these were significantly higher than those for LBP (AUC0.566) on admission.Conclusions On admission and 24 h later, the LBP concen-tration is less accurate for predicting bacteremia/clinical sepsiscompared to IL-6, PCT, and CRP.

Keywords Febrile neutropenia . Lipopolysaccharide-bindingprotein . Bacteremia . Sepsis . Children

Introduction

Patients with severe neutropenia (<500 neutrophils/mm3) arevery prone to bacterial infections [1]. The risk of bacterialinfection is related to the degree and duration of neutropenia[1]. In severely neutropenic patients, it is difficult to diagnosebacterial infection due to the lack of local signs of inflamma-tion, as fever may be the only sign. Moreover, the clinicalcriteria for the diagnosis of the systemic inflammatory re-sponse syndrome (SIRS) and sepsis are difficult to applybecause of the presence of neutropenia [2, 3]. In about halfof febrile neutropenic children, the cause of fever remainsundetermined [4]. These patients are classified as having feverof unknown origin (FUO). Due to difficulties in diagnosingbacterial infection and since bacterial infections in neutropenicpatients may lead to life-threatening complications, routinehospitalization and prompt initiation of broad-spectrum intra-venous antibiotics is the common approach in patients withfebrile neutropenia (FN). However, such an approach may betoo aggressive for a considerable number of patients. There is awide range of different approaches to risk stratification, largely

L. Kitanovski (*) : J. JazbecDivision of Hemato-Oncology, Department of Pediatrics, UniversityMedical Center Ljubljana, Ljubljana, Sloveniae-mail: lidija.kitanovski@kclj.si

S. HojkerNuclear Medicine Department, University Medical Center Ljubljana,Ljubljana, Slovenia

M. DergancDepartment of Pediatric Surgery and Intensive Care, UniversityMedical Center Ljubljana, Ljubljana, Slovenia

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built on clinical data [5–7], but these demonstrate only moderatediscriminatory ability.

Therefore, an early biomarker of bacterial infection at theonset of a febrile episode would be very useful. Currently, themost widely used biomarker is C-reactive protein (CRP),which, however, has several disadvantages, such as its de-layed increase and low specificity. In recent years, severalbiomarkers have been studied in FN, including procalcitonin(PCT) and interleukin-6 (IL-6). PCT was found to be usefulfor differentiating between systemic forms of infection andnon-infectious fever [8], while IL-6 exhibits the potential to bea better early discriminator than CRP for those childrenwho will develop a serious complication [9]. Recently,lipopolysaccharide-binding protein (LBP) has proven su-perior to PCT in diagnosing sepsis in critically ill non-immunocompromised newborns and children [10, 11]. Onlyone study has so far evaluated its diagnostic role in predomi-nantly adult febrile neutropenic patients [12], revealing highsensitivity and specificity of LBP for predicting Gram-negative(GN) bacteremia.

LBP, synthesized mainly in the liver and endothelial cells,binds to lipopolysaccharide (LPS), a component of the outercell wall of GN bacteria, and transfers LPS to CD14 protein[13]. By facilitating binding to the CD14 cell membranemolecules, LBP enhances the sensitivity of monocytes andgranulocytes to LPS [14], whereas the soluble form of CD14mediates LPS activation of CD14-negative cells [15]. CD14can only bind LPS in the presence of LBP, and although LPSis considered its main ligand, CD14 also recognizes other mi-crobial constituents, which include the proteoglycans of Gram-positive (GP) bacteria. Thus, besides its well-established role inGN infections, LBP has a more expanded role as a generalrecognition molecule [13]. Binding to signaling Toll-like recep-tors (TLR) on effector cells leads to the production of inflam-matory cytokines [16], resulting from LPS signaling throughTLR-4 and proteoglycan signaling through TLR-2 [16].

LBP has been reported to rise in adults with bacterial GNand GP, as well as in fungal, infections [17]. Increased LBPconcentrations have also been reported in children with inva-sive bacterial, but not viral, infections [18, 19].

The aims of the present study were to determine the earlydiagnostic accuracy of LBP for predicting bacteremia/clinicalsepsis and to compare it with the diagnostic accuracy of themore frequently used PCT, IL-6, and CRP and with maximumbody temperature on admission (TMAX) in febrile neutropenicchildren.

Methods

This prospective study was performed in the PediatricHemato-Oncology Department of the University Medical

Center Ljubljana during a 17-month period (from November2007 to March 2009).

Patients with FN (defined as an increase in body tempera-ture to >38.5 °C once or >38 °C on two or more occasionsduring a 12-h period, with an absolute neutrophil count of<500/mm3 or between 500 and 1,000/mm3 when the count isanticipated to fall below 500/mm3 within 48 h) were eligiblefor enrollment.

Episodes of FN were divided into four groups:

& Group 1—bacteremia and/or clinical sepsis. Bacteremiawas defined as the presence of live bacteria in the blood-stream [2], and clinical sepsis was defined as fever witheither hypotension or oliguria, and all of the following:microorganism not isolated from the blood, no apparentinfection at another site, and appropriate antimicrobialtherapy for sepsis instituted by the physician [20].

& Group 2—local infection. This is defined as localized,clinically, and/or microbiologically documented infection,defined according to the recommendations of the GermanSociety of Hematology and Oncology DGHO [21, 22].

& Group 3—FUO. This is defined as an episode of feverwithout a recognizable cause [21, 22].

& Group 4—others . Patients with probable invasive fungalinfection, defined according to the established definitionof the EORTC/MSG Consensus Group [23], and patientswith documented viral infection and paraneoplasticfever were included. Paraneoplastic fever was diag-nosed according to the criteria listed by Penel and co-workers [24].

Patients in group 1 were divided into subgroups: those withsevere sepsis (presentation as septic shock or sepsis associatedwith organ dysfunction, hypotension, or hypoperfusion abnor-malities) and those with non-severe sepsis. Additionally, theywere divided into those with GP, GN, and polymicrobialbacteremia.

From each patient, at least two blood samples (one from aperipheral vein and one from the central venous catheter(CVC), or two consecutive samples from a peripheral veinwhen no CVC was in place), urine, and stool were obtainedfor bacterial cultures. Additional biological materials wereobtained for bacterial and fungal cultures and for viral testswhen clinically indicated. Complete white blood cell countsand CRP concentration measurements were checked daily.

In addition, 1–2mL of bloodwas obtained for PCTand 3mLfor LBP and IL-6 concentration measurements on two consec-utive days (on day 1, before antibiotics were initiated; and onday 2, 24±6 h after the first sample was taken). CRP and PCTconcentrations were determined immediately by theimmunoturbidimetric method (QuickRead CRP, OrionDiagnostica, Finland; determination range 8–160 mg/L) andelectrochemiluminiscence immunoassay, respectively

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(ELECSYS® B·R·A·H·M·S PCT, Roche Diagnostics,Germany; determination range 0.02-100 μg/L; functional sensi-tivity 0.06 μg/L). For LBP and IL-6 determination, plasma wasseparated from the cells and stored at −70 °C. LBP concentra-tions were determined by chemiluminiscent immunometric as-say (Immulite LBP, DPC, Los Angeles, USA, determinationrange 0.2–200 mg/L) and IL-6 by chemiluminiscent sequentialimmunometric assay (Immulite IL-6, DPC, Los Angeles, USA,determination range 5–1,000 ng/L).

Additionally, data on body temperature on admission(TMAX) were collected.

Data were analyzed for sensitivity, specificity, positivepredictive value (PPV), and negative predictive value (NPV)derived from the receiver operating characteristic (ROC)curves. The diagnostic accuracies of LBP, PCT, IL-6, andCRP were expressed as the areas under the ROC curves(AUC) and compared according to Hanley and McNeil [25].

Comparison between groups was made by the Mann–Whitney test and the Kruskal–Wallis non-parametric analysisof variance. The proportions of patients were compared by theχ2 test. Differences at the level of p <0.05 were consideredstatistically significant.

Statistical analysis was performed using IBM SPSSStatistics (version 19; SPSS Inc., IBM Company, Chicago,IL, USA) and MedCalc for Windows (version 5.0; MedCalcSoftware, Mariakerke, Belgium).

The study was approved by the National Medical EthicsCommittee, and written consent was obtained from parents orpatients for additional blood sampling.

Results

The concentration of LBP, PCT, IL-6, and CRP was deter-mined for 90 episodes of FN experienced by 48 patients (24girls and 24 boys); 31 patients experienced one episode of FNand 17 patients experienced two to six episodes. The shortestafebrile interval between two episodes of FN was 14 days.The initial neutrophil count was <0.5×109/L in 82/90 epi-sodes and 0.5–1.0×109/L in 8/90 episodes. Patient character-istics for each group are shown in Table 1.

Episodes of FN were classified as follows:

& Group 1: 18 episodes (bacteremia 16, clinical sepsis 2)& Group 2: 12 episodes (pneumonia 4, abscess 1, cellulitis 3

(2 caused by Pseudomonas aeruginosa ), urinary tractinfection caused by Escherichia coli 1, pharyngitis causedby Streptococcus pyogenes 2, colitis caused byClostridium difficile 1)

& Group 3: 49 episodes of FUO& Group 4: 11 episodes (confirmed viral infection 6—

respiratory syncytial virus 2, influenza 2, adenovirus1, and calicivirus 1; probable aspergillosis 3, paraneoplasticfever 2)

There were no differences between groups in terms of age,duration of fever before sampling, sex, underlying disease,and presence of mucositis, whereas initial absolute neutrophiland monocyte counts and TMAX before blood sampling dif-fered significantly between the groups (Table 1).

In group 1, there were 8 episodes of severe and 10 episodesof non-severe sepsis. Of the 16 bacteremia episodes, there were7 episodes of GP bacteremia (Staphylococcus warneri 1,Staphylococcus epidermidis 2, Streptococcus mitis 3,Streptococcus spp 1), 8 episodes of GN bacteremia (E. coli 3,P. aeruginosa 2, Enterobacter cloacae 1,Neisseria subflava 1,Acinetobacter lwofii 1), and 1 polymicrobial bacteremia (A.lwofii , Streptococcus mitis). The percentage of severe sepsisamong patients with GN bacteremia (50 %) was higher thanamong patients with GP bacteremia (28.6%), but the differencewas not significant (p =0.76).

The median concentration, concentration range, andp values of the studied biomarkers by groups and subgroupsare presented in Tables 2 and 3.

The concentrations of all biomarkers were significantlyhigher in patients with bacteremia/clinical sepsis than in thosewith non-bacteremia/clinical sepsis episodes on both days(pCRP1=0.01, pCRP2=0.00, p PCT1=0.03, p PCT2=0.00,pLBP1=0.05, pLBP2=0.01, p IL1=0.00, p IL2=0.00). The differ-ence in LBP concentration on day 1 was borderline significant(p =0.054).

In patients with GN bacteremia, the median concentrationof all studied biomarkers (except IL-6 on day 1) was higherthan in patients with GP bacteremia, but no difference wasstatistically significant.

In patients with severe sepsis, the LBP concentration washigher than in those with non-severe sepsis, but the differencewas not significant. Only the IL-6 concentration on day 1 andthe IL-6 and PCT concentrations on day 2 were significantlyhigher in patients with severe vs. non-severe sepsis.

The results of ROC analysis for prediction of bacteremia/clinical sepsis and severe sepsis are presented in Table 4 andFigs. 1 and 2. The diagnostic accuracy of TMAX (AUC 0.668)did not significantly differ from the AUCs of the studiedbiomarkers. At the best cutoff value (COV) of 39 °C, thesensitivity was 47.1 %, specificity 88.4 %, PPV 50 %, andNPV 87.1 %.

Discussion

A reliable, specific, and sensitive biomarker, which is inde-pendent of leukocyte count and underlying disease, is neededfor the early diagnosis of infection in patients with FN. Anideal marker would be able to reliably stratify the patients withFN and consequently enable treatment of a subset of patientsin outpatient settings with oral antibiotics.

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Table 2 The median concentrations and concentration ranges of studied parameters by individual group on days 1 and 2

Group 1 (n=18) median (range) Group 2 (n =12) median (range) Group 3 (n =49) median (range) Group 4 (n=11) median (range)

CRP.1 (mg/L) 108.0 (3–290) 63.0 (9–257) 39.0 (3–219) 26.0 (3–362)

pFUO 0.01 0.19

p1/2 0.41

CRP.2 (mg/L) 238.0 (9–488) 86.0 (31–472) 57.0 (3–374) 35.0 (8–286)

pFUO 0.00 0.04

p1/2 0.09

PCT.1 (μg/L) 0.31 (0.08–152.00) 0.48 (0.04–9.09) 0.14 (0.04–9.27) 0.15 (0.04–0.65)

pFUO 0.02 0.11

p1/2 0.73

PCT.2 (μg/L) 6.26 (0.04–89.53) 1.14 (0.06–10.94) 0.29 (0.04–11.80) 0.20 (0.04–0.37)

pFUO 0.00 0.05

p1/2 0.18

LBP.1 (mg/L) 28.85 (2.7–1,220.0) 20.90 (13.3–57.9) 18.30 (9.6–89.3) 16.4 (5.4–28.3)

pFUO 0.10 0.40

p1/2 0.20

LBP.2 (mg/L) 33.90 (4.2–149.0) 26.30 (14.9–74.6) 18.40 (7.3–89.5) 14.1 (9.6–27.4)

pFUO 0.01 0.09

p1/2 0.27

IL6.1 (ng/L) 128.00 (13.9–6,640.0) 77.85 (28.2–551.0) 29.60 (3.1–429.0) 27.2 (3.2–167.0)

pFUO 0.00 0.01

p1/2 0.27

IL6.2 (ng/L) 67.65 (4.9–7,520.0) 55.80 (7.7–1,920.0) 27.2 (3.2–167.0) 18.2 (6.4–102.0)

pFUO 0.00 0.01

p1/2 0.58

Group 4 was excluded from the statistical analysis

Group 1 bacteremia/clinical sepsis (bacteremia 16, clinical sepsis 2), Group 2 local infection, Group 3 fever of unknown origin, Group 4 others (viralinfection 6, probable invasive fungal infection 3, paraneoplastic fever 2), pFUO probability (p) value resulting from the statistical comparison of theconcentration of biomarker in the individual groups with group 3 (FUO) (Mann–Whitney test), p1/2 probability (p) value resulting from the comparisonof the concentration of biomarker in group 1 with group 2 (Mann–Whitney test)

Table 1 Patient characteristics in individual study groups

All episodes n =90(100 %)

Group 1 n =18(20 %)

Group 2 n=12(13.3 %)

Group 3 n =49(54.4 %)

Group 4 n =11(12.2 %)

pvalueb

Age (years), median (range) 6.3 (0.5–19.9a) 9.3 (1.25–19.9a) 7.0 (0.5–15.3) 5.3 (0.7–16.7) 5.0 (1.2–15.3) 0.51

Sex (M/F) 40/50 9/9 7/5 21/28 3/8 0.47

Underlying disease (HD/ST) 60/30 15/3 6/6 30/19 9/2 0.14

Fever duration before admission (h),median (range)

5.0 (0.3–40.0) 5.2 (0.5–18.0) 4.3 (1.0–40.0) 5.0 (0.3–24.0) 7.6 (1.5–24.0) 0.82

TTMAX 38.6 (38–39.8) 39.0 (38–39.8) 38.8 (38.5–39.8) 38.6 (38–39.7) 38.4 (38–39.0) 0.01

Mucositis (yes/no) 17/73 3/14 3/9 10/40 1/10 0.78

ANC, median (per μL) (range) 0 (0–997) 0 (0–39) 84 (0–924) 0 (0–997) 0 (0–947) 0.02

AMC, median (per μL) (range) 0 (0–1,092) 0 (0–80) 87 (0–777) 0 (0–1,092) 0 (0–742) 0.03

Group 1 bacteremia/clinical sepsis, Group 2 local infection, Group 3 fever of unknown origin, Group 4 others (viral infection 6, probable invasivefungal infection 3, paraneoplastic fever 2),M male, F female, HD hematologic disease, ST solid tumor, h hours, ANC absolute neutrophil count, AMCabsolute monocyte count, TTMAX maximum body temperature on admission (before first blood sampling)a Only one patient of 19.9 years of age. All other patients were under 18 years of agebKruskal–Wallis test

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Since its initial description, LBP has gained attention as apotential new biomarker of infection. It has proven superior toPCT in diagnosing sepsis in critically ill newborns and chil-dren [10, 11]. We hypothesized that it could also be a prom-ising marker in FN patients. Only two studies have previouslyevaluated LBP in cancer patients with infection [12, 26]. Toour knowledge, however, no study has yet evaluated thediagnostic accuracy of LBP for predicting bacteremia/clinical sepsis in children with FN, and no study has comparedLBP with PCT and IL-6.

In our study, LBP concentrations on admission in patientswith bacterial infection did not differ from those in patientswith FUO. The LBP concentration on admission was higher

than the upper limit of normal (>15.2 mg/L) in 80.0 % ofpatients with bacterial infection and in 71.4 % of patients withFUO. The difference was not significant. The median concen-trations of LBP on admission in patients with bacterial infec-tion and FUO were 24.3 and 18.3 mg/L, respectively. Wespeculate that the unexplained fever and the considerableelevation of LBP found in the majority of FUO episodesmight be a consequence of endotoxemia, as disruption of themucosal barrier allows endogenous bacterial products, includ-ing LPS, to enter the circulation [27]. FUO, in the setting ofFN, can therefore be considered similar to non-infectiousSIRS. There is a dearth of studies examining this assumption.The median LBP concentration in our patients with FUO is

Table 3 The median concentrations and concentration ranges of studied parameters by individual subgroup on days 1 and 2

GNB (n =8) median (range) GPB (n=7) median (range) p Severe sepsis (n =8) median (range) Non-severe sepsis(n =10) median (range)

p

CRP.1 (mg/L) 109.5 (34–290) 57.0 (3–237) 0.28 73.0 (8–290) 128.5 (3–237) 0.96

CRP.2 (mg/L) 258.5 (54–426) 184.0 (9–488) 0.61 294.0 (153–426) 191.5 (9–488) 0.08

PCT.1 (μg/L) 0.31 (0.08–126.60) 0.14 (0.09–9.76) 0.34 5.37 (0.08–152.10) 0.23 (0.10–2.84) 0.24

PCT.2 (μg/L) 11.71 (0.04–89.53) 0.41 (0.09–13.64) 0.19 15.89 (7.70–89.53) 0.36 (0.04–50.26) 0.00

LBP.1 (mg/L) 39.05 (3.9–1,220.0) 25.60 (2.7–36.6) 0.23 36.85 (2.7–1,220.0) 28.85 (3.9–64.7) 0.90

LBP.2 (mg/L) 44.70 (4.2–149.0) 25.40 (11.4–49.7) 0.28 57.60 (10.9–149.0) 31.85 (4.2–104.0) 0.31

IL6.1 (ng/L) 100.60 (27.5–1,930.0) 129.00 (13.9–661.0) 0.69 990.50 (42.2–6,640.0) 88.15 (13.9–982.0) 0.03

IL6.2 (ng/L) 67.55 (4.9–3,064.0) 41.10 (10.7–3,788.0) 0.96 1,108.00 (29.8–7,520.0) 38.75 (4.9–181.0) 0.00

GNB Gram-negative bacteremia, GPB Gram-positive bacteremia

Table 4 The best cutoff value, sensitivity, specificity, positive predictivevalue (PPV), negative predictive value (NPV), and area under thecurve (AUC) of C-reactive protein (CRP), procalcitonin (PCT),

lipopolysaccharide-binding protein (LBP), and interleukin-6 (IL-6) con-centrations on days 1 and 2 for predicting bacteremia/clinical sepis andsevere sepsis

Biomarker Bacteremia/clinical sepsis Severe sepsis

AUCa COV Sens Spec PPV NPV AUCb COV Sens Spec PPV NPV

CRP (mg/L)

Day 1 0.695 >120 50.0 87.3 50.0 87.3 0.628 >202 37.5 93.8 37.5 93.7

Day 2 0.828 >147 77.8 85.7 58.3 93.7 0.911 >147 100 79.7 33.3 100

PCT (μg/L)

Day 1 0.665 >1.35 38.9 91.7 53.8 85.7 0.752 >1.35 62.5 90.1 38.5 96.1

Day 2 0.744 >2.27 61.6 87.7 57.9 89.1 0.981 >5.1 100 93.2 61.5 100

LBP (mg/L)

Day 1 0.648 >26.7 61.1 76.8 40.7 88.3 0.566 >46.2 50.0 92.3 40.0 94.7

Day 2 0.714 >22.1 77.8 69.1 40.0 92.9 0.714 >52.0 62.5 90.9 41.7 95.9

IL6 (ng/L)

Day 1 0.775 >41.8 83.3 60.0 34.9 93.9 0.892 >241 75.0 92.4 50.0 97.3

Day 2 0.775 >29.3 77.8 72.1 42.4 92.5 0.924 >76.7 87.5 85.7 38.9 98.5

a AUCs of studied biomarkers did not differ significantly (p <0.05)b On day 1, the AUCIL6 was significantly higher thanAUCCRP (p =0.03) andAUCLBP (p =0.01), but not significantly higher than AUCPCT (p=0.15). Onday 2, the diagnostic accuracy of LBP (AUCLBP) was significantly lower than that of AUCCRP (p =0.04) and AUCPCT (p =0.01), but not that of AUCIL6

(p =0.06). AUCs were compared according to Hanley and McNeil

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within the range of the median concentrations of LBP in SIRS/no sepsis published in the literature, although they vary widely[10, 11, 28]. It is comparable to the median LBP concentrationin the FUO group of the only published study evaluating thediagnostic usefulness of LBP in patients with FN [12]. Themedian LBP concentration in their FUO group was 21.2 mg/L. However, our results of the diagnostic accuracy of LBP

differ from theirs [12]. They found a significantly highermedian LBP concentration in patients with GN bacteremiacompared to those with GP bacteremia and FUO. LBP had ahigh sensitivity (100 %) and specificity (92 %) for identifyingpatients with GN bacteremia at a COVof 46.3 mg/L. In theirstudy, the median LBP concentration in patients with GNbacteremia was considerably higher (54.2 mg/L) than theconcentration in our patients (39.1 mg/L), but there were onlya small number of these patients in both studies. In our study,the median concentration of LBP in patients with bacteremia/clinical sepsis was 28.8 mg/L, which is comparable to that ofnon-immunocompromised patients with sepsis in the recentpediatric study conducted by Pavare [19]. The best COVs arealso comparable in both studies (26.7 mg/L in our study and26.6 mg/L in Pavare's).

In other studies conducted in critically ill children, the bestCOVs for diagnosing sepsis differ considerably (from 13.3 to47.6 mg/L) [10, 11, 28]. The highest COVof LBP for identi-fying sepsis (47.6 mg/L) was observed in the study of Pavcnik-Arnol [28], where 30 % of septic patients had septic shock and67 % had severe sepsis. Their COV for diagnosing severesepsis is comparable to ours (46.7 mg/L). The correlationbetween the severity of infection and LBP concentration isunclear, as the results of different studies are contradictory[10, 19]. In our study, the LBP concentration in patients withsevere sepsis was higher, but the difference was not significant.

In critically ill newborns and children, LBP predicted sep-sis better than PCTand IL-6 [10, 28]; however, in adults, PCTperformed better than LBP [29]. In a pediatric study ofcommunity-acquired infections and bacteremia conducted byPavare, LBP, IL-6, and CRP had comparable diagnostic accu-racies for bacteremia [19].

PCT was found to be helpful in differentiating systemicforms of infection from non-infectious etiologies of fever, butit could not discriminate between GN and GP infections [8,30]. The results of a recent systematic review of the predictivevalues of serum markers of infection in children with FNsuggest the superior predictive value of PCT over CRP [9].However, the data showed significant inconsistencies, andPCT cannot yet be recommended for use in routine clinicalpractice [9]. Based on the samemeta-analysis, IL-6 has shownthe potential to be a better early discriminator than CRP ofthose children who will develop a serious infectious compli-cation [9]. The authors concluded that both biomarkers appearpromising and should be subject to new primary studies.

In our study, the diagnostic accuracies of PCT and IL-6were comparable to that of CRP. Our results are similar tothose of the most recent meta-analysis, in which a comparablediagnostic accuracy of CRP and PCT for severe infection inpediatric patients with FN was demonstrated [31]. The compa-rable concentrations of both markers in severe bacterial infec-tion can partly be explained by the specificity of the immuneresponse in neutropenic patients. Lower PCT and higher CRP

ON ADMISSION

Fig. 1 ROC curves comparing LBP, PCT, IL-6, and CRP for predictionof bacteremia/clinical sepsis on admission. AUCs of the studied bio-markers did not differ significantly (p>0.05)

AT 24 H

Fig. 2 ROC curves comparing LBP, PCT, IL-6, and CRP for predictionof bacteremia/clinical sepsis at 24 h. AUCs of the studied biomarkers didnot differ significantly (p >0.05)

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concentrations have been found in febrile neutropenic patientswith bacterial infection in comparison to febrile non-neutropenic cancer patients [32, 33].

In our study, the most sensitive biomarker for predictingbacteremia/clinical sepsis was IL-6, whereas PCT had the bestspecificity. In our previous study, the initial PCT and IL-6concentrations in patients with bacteremia/clinical sepsis werehigher [30]. This may be explained by a higher percentage ofsevere sepsis in the previous study. In both studies, we showedthat PCTand IL-6 concentrations are the best predictors of theseverity of the sepsis. In severe sepsis, at a sensitivity level of100 %, the best specificity on day 1 was seen for IL-6(specificity 57 %) at a cutoff value of 41.8 mg/L and on day2 for PCT (specificity 93.2 %) at a cutoff value of 5.1 μg/L.Interleukin-6 has already been shown to be a good predictor ofserious complications [9]. The usefulness of PCT forpredicting the severity of infection was also confirmed in otherstudies [34], whereas Santolaya found that the biomarkersindependently associated with severe sepsis on admissionand after 24 h were CRP (≥90/100 mg/L) and IL-8 (≥200/300 pg/mL), but not PCT (IL-6 was not investigated) [35].

The most widely used biomarker, CRP, increases slowly,and several sequential determinations are necessary for a moreaccurate diagnosis of infection [36]. Moreover, CRP levelscan be influenced by the underlying malignant disease andtissue damage; hence, its specificity is low [37]. In our study,for predicting bacteremia/clinical sepsis, the best COVof CRPand TMAXwas 90mg/L and 39 °C, respectively. Inmost of thelarge studies, the high-risk group and invasive bacterial infec-tion were best predicted at a CRP level of >90 mg/L [34, 37,38] and an admission body temperature of >39 °C [38, 39].

In neutropenic cancer patients, the usefulness of differentbiomarkers of bacterial infection might be influenced not onlyby different etiologies of infection by bacteria that rarely causebacteremia in non-neutropenic patients, but also by impairedneutrophil numbers. The impact of neutropenia on biomarkerconcentration has already been demonstrated for PCT andCRP. Lower PCT concentrations have been found inneutropenic patients with bacterial infection [32, 40], where-as Povoa found significantly higher CRP concentrations incritically ill septic neutropenic than in non-neutropenic cancerpatients [33].

A reduction in diagnostic accuracy in neutropenic patientshas been suggested for markers that are expressed on activatedneutrophils and monocytes, e.g., the recently studied FcγRIreceptor (CD64) and soluble triggering receptor expressed onmyeloid cells-1 (TREM-1). Several studies reported the po-tential utility of CD64 for the diagnostic assessment of sepsisin neonates, children, and adults [11, 41, 42]. Groselj-Grencfound that the neutrophil CD64 index is the best early marker ofbacterial sepsis in critically ill children [11]. No data exist,however, regarding the utility of CD64 in FN. The granulocytecolony-stimulating factor, often used in children with cancer,

can upregulate CD64 expression on neutrophils [43]. Therefore,CD64, despite its good diagnostic accuracy for sepsis in non-neutropenic patients [11], might not be a very good marker inneutropenic cancer patients. Only two studies have recentlyevaluated the usefulness of TREM-1 in patients with FN, withconflicting results. Kwofie et al. found that TREM-1 iselevated in high-risk adult patients with FN and is potentiallyuseful to predict their clinical course [44], whereas Miedemadid not find it suitable as a marker of bacterial infection inchildren with FN [45].

Some limitations of our study merit consideration. Firstly,we are well aware of the lack of universally acceptable defi-nitions of FN in different studies. Serious inconsistencies existbetween studies in terms of heterogeneity of the studiedpopulations and study methodologies, which has led to poorcomparability between studies. Secondly, this was a singlecenter study with a relatively small number of FN events andconfirmed cases of bacteremia. However, the number of FNepisodes included in our study is comparable to most of thepublished single center studies evaluating the role of bio-markers in children with FN.

In conclusion, data from the present study indicate that, onadmission and 24 h later, LBP concentration is less accuratefor predicting bacteremia/clinical sepsis in febrile neutropenicchildren than PCT, IL-6, and CRP and TMAX on admission.

Our data suggest that LBP concentrations in neutropenicseptic patients are comparable to those in non-neutropenicpatients with sepsis. However, due to the shortage of data,the influence of neutropenia on LBP concentration in patientswith bacterial infection cannot be ascertained. In order toimprove risk stratification in children with FN, new ap-proaches are needed (e.g., genetic studies of polymorphism).

Acknowledgments This study was supported by the Slovenian Re-search Agency, grants no. J3-2184 and J3-4220. The authors thank Dr.Dianne Jones for language review.

Conflict of interest All authors declare no conflict of interest. Authorshave full control of all primary data and agree to allow the journal toreview their data if requested.

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