Correlation of pyuria and bacteriuria in acute care
Background
Pyuria is often used as an important marker in the diagnosis of urinary tract infection . Interpretation of pyuria may be especially important in patients with nonspecific complaints. There is a paucity of data to demonstrate the usefulness of pyuria alone in the diagnosis of bacteriuria or urinary tract infection.
This study aims to further define the relationship of pyuria and positive bacterial growth in urine culture, as well as the diagnostic utility of different urinary white blood cell cut-off points.
Method
A total of 46,127 patients over the age of 18 years were selected from the inpatient population of HCA Healthcare System Capital Division . Urine microscopy results were stratified by white blood cell count and correlated with the positivity of bacterial growth in urine culture. The optimal cutoff point for urinary white blood cells was derived based on the receiver operating characteristic curve plot.
Results
Urine microscopy finding of white blood cells 0-5 cells/hpf, 5-10 cells/hpf, 10-25 cells/hpf, and more than 25 cells/hpf was associated with 25.4%, 28.2%, 33 % and 53.8% bacteriuria rates, respectively.
The receiver operating characteristic curve plot demonstrated that pyuria alone did not provide adequate diagnostic accuracy for predicting bacteriuria. The optimal cutoff point for the best combination of sensitivity and specificity was found to be 25 cells/hpf.
Conclusions
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Comments
Pyuria is common in asymptomatic bacteriuria (ASB) and urinary tract infections (UTI), but it is unknown whether the degree of pyuria is useful in predicting bacteriuria. In this cross-sectional study, researchers from a single US health system compared urine culture positivity rates at four white blood cell per high-power field (WBC/hpf) cut-off points to define an optimal pyuria as a predictor of bacteriuria. Data were extracted from 46,000 hospitalizations of adults (mean age, 57; 80% women) who underwent urinalysis and urine culture.
Bacteriuria was defined as any bacterial growth in the urine culture, regardless of the amount. At WBC/hpf cutoffs of 0 to 5, 5 to 10, 10 to 25, and >25, the prevalence of bacteriuria was 25%, 28%, 33%, and 54%, respectively, a statistically significant trend.
The positive predictive value between the cut-off points ranged from 45% to 55%, and the negative predictive value ranged from 70% to 80%. In patients with positive cultures, bacterial growth exceeded 50,000 colony-forming units per ml approximately 80% of the time, even among those with only 0 to 5 WBC/hpf.
A limitation of this study is the lack of data on symptoms, which makes it impossible to differentiate ASB from UTI. Despite this limitation, these results confirm that a higher degree of pyuria is associated with a higher probability of bacteriuria.
However, the relatively low positive and negative predictive values mean that the degree of pyuria alone does not provide sufficient information to reliably predict bacteriuria (much less UTI) and should not supplant clinical judgment in treatment decisions with antibiotics.
