Objective: To compare the validity of the urinalysis on clean-voided bag versus catheter urine specimens using the catheter culture as the "gold" standard.
Study design: This is a cross-sectional study of 303 nontoilet-trained children under age 3 years at risk for urinary tract infection (UTI) who presented to a children's hospital emergency department. Paired bag and catheter specimens were obtained from each child and sent for dipstick and microscopic urinalysis. Sensitivity and specificity were compared using McNemar's chi2 test for paired specimens and the ordinary chi2 test for unpaired comparisons.
Results: The bag dipstick was more sensitive than the catheter dipstick for the entire study sample: 0.85 (95% confidence interval [CI]=0.78 to 0.93) versus 0.71 (95% CI=0.61 to 0.81), respectively. Both bag and catheter dipstick sensitivities were lower in infants < or =90 days old (0.69 [95% CI=0.44 to 0.94] and 0.46 [95% CI=0.19 to 0.73], respectively) than in infants >90 days old (0.88 [95% CI=0.81 to 0.96] and 0.75 [95% CI=0.65 to 0.86], respectively). Specificity was consistently lower for the bag specimens than for the catheter specimens: 0.62 (95% CI=0.56 to 0.69) versus 0.97 (95% CI=0.95 to 0.99), respectively.
Conclusions: Urine collection methods alter the diagnostic validity of urinalysis. These differences have important implications for the diagnostic and therapeutic management of children with suspected UTI.