Diagnostic Accuracy of the Quantitative C-Reactive Protein, Erythrocyte Sedimentation Rate and White Blood Cell Count in Urinary Tract Infections among Infants and Children

Objectives: The aim of this study was to evaluate the diagnostic accuracy of the quantitative C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and white blood cell (WBC) count in urinary tract infections (UTI) among hospitalised infants and children in Qazvin, Iran.
Methods: This cross-sectional study was conducted on 127 hospitalised children ranging in age from 2 months to 12 years old 31.79 months (SD 30.73) who were suspected of having a UTI and who did not receive antibiotics prior to being seen at a Qazvin teaching children’s hospital between 2005 and 2006. A urine analysis (U/A) and urine culture (U/C) were performed. The blood was taken for CRP, ESR and WBC analyses. U/C has been considered the gold standard test for a UTI and dimercaptosuccinic acid renal scintigraphy (DMSA) as the gold standard for an upper UTI (pyelonephritis). These tests were used to determine the diagnostic accuracy, which is represented as the percent of correct results.
Results: Within the study population, 72 patients (56.7%) were younger than two years old 9.86 months (SD 4.56) and 55 (43.3%) were older than two years old 63.58 months (SD 30.96). One hundred and two patients (80.3%) were female. There were 100 cases that had a positive U/C. Of the patients with a positive U/C, 81 had pyuria (WBC more than 5/hpf), 71 had a peripheral WBC count of more than 10 000 /mL, 95 had a CRP of more than 10 mg/L and 82 had an ESR > 10 mm/h. The sensitivity and specificity as well as the positive and negative predictive values and the accuracy of CRP when using U/C as the gold standard were, respectively, 96%, 11.1%, 80.2%, 50%, and 78%; when using ESR as the gold standard were, respectively, 55%, 40%, 77.6%, 17.2%, and 52%; and when using WBC counts as the gold standard were, respectively, 69%, 52%, 86.6%, 35.6%, and 65%. The accuracy of CRP, ESR and WBC counts when considering the DMSA as the gold standard were 58.3%, 62.8%, and 64.5%, respectively.
Conclusion: Although acute phase reactants can help in the diagnosis of a UTI, they are not pathognomonic. CRP, ESR and WBC were neither completely sensitive nor specific for detecting a UTI and its localisation site in Iranian children. Therefore, in a country where advanced clinical diagnostic tests are available, the advanced test should be used in conjunction with CRP, ESR and WBC analyses. Finally, a combination of laboratory tests along with history and exact clinical examination are needed for the diagnosis of a UTI and its localisation site.

Keywords
children; DMSA renal scintigraphy; erythrocyte sedimentation rate; Urinary tract infection; quantitative C-reactive protein