Introduction Significant pyuria is not always present in infants with urinary tract infection (UTI), thus complicating the approach of febrile infants without obvious source of fever.
Purpose To assess the incidence of UTI without significant pyuria and the ability of certain clinical and laboratory parameters in predicting non-significant pyuria UTI among febrile young infants.
Methods Retrospective study of all febrile infants (rectal temperature >38°C), aged 29–180 days, admitted between 2001 and 2007, for the evaluation of fever without source. Significant pyuria was defined as >10 white blood cell count (WBC)/high power field.
Results Of 786 infants enrolled, 217 (27.6%) were diagnosed with UTI and 78 of these (32.7%) had no significant pyuria. Potential predictors of non-significant pyuria UTI, as identified by logistic regression, included: male gender (p = 0.004), fever >36 h (p = 0.003) and the absence of upper respiratory infection symptoms (p<0.001). Receiver operator characteristic curve analysis revealed similar predictive ability for WBC (area under the curve (AUC) 0.651), absolute neutrophil count (AUC 0.635) and platelet count (AUC 0.680). WBC >15 000/mm3 would predict only 43.6% (34/78) of non-significant pyuria UTI, whereas the combination of WBC >15 000/mm3 and platelet count >450 000/mm3 would lead to the successful prediction of 78.2% (61/78) of UTI without significant pyuria.
Conclusions In our study, approximately 1/3 of the infants with UTI had no significant pyuria. Early identification of these infants is challenging, as the clinical signs are not specific and the commonly used laboratory tests (such as WBC) lack adequate predictive ability. Yet the combination of platelet count >450 000/mm3 and WBC >15 000/mm3, could be useful in identifying infants at risk of UTI among febrile infants without significant pyuria.
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