Abstract
ABSTRACTObjective To investigate whether the urine dipstick screening test can be used to predict urine culture results.Methods A retrospective study conducted between January and December 2014 based on data from 8,587 patients with a medical order for urine dipstick test, urine sediment analysis and urine culture. Sensitivity, specificity, positive and negative predictive values were determined and ROC curve analysis was performed.Results The percentage of positive cultures was 17.5%. Nitrite had 28% sensitivity and 99% specificity, with positive and negative predictive values of 89% and 87%, respectively. Leukocyte esterase had 79% sensitivity and 84% specificity, with positive and negative predictive values of 51% and 95%, respectively. The combination of positive nitrite or positive leukocyte esterase tests had 85% sensitivity and 84% specificity, with positive and negative predictive values of 53% and 96%, respectively. Positive urinary sediment (more than ten leukocytes per microliter) had 92% sensitivity and 71% specificity, with positive and negative predictive values of 40% and 98%, respectively. The combination of nitrite positive test and positive urinary sediment had 82% sensitivity and 99% specificity, with positive and negative predictive values of 91% and 98%, respectively. The combination of nitrite or leukocyte esterase positive tests and positive urinary sediment had the highest sensitivity (94%) and specificity (84%), with positive and negative predictive values of 58% and 99%, respectively. Based on ROC curve analysis, the best indicator of positive urine culture was the combination of positives leukocyte esterase or nitrite tests and positive urinary sediment, followed by positives leukocyte and nitrite tests, positive urinary sediment alone, positive leukocyte esterase test alone, positive nitrite test alone and finally association of positives nitrite and urinary sediment (AUC: 0.845, 0.844, 0.817, 0.814, 0.635 and 0.626, respectively).Conclusion A negative urine culture can be predicted by negative dipstick test results. Therefore, this test may be a reliable predictor of negative urine culture.
Highlights
Urinary tract infection is one of the most common infections and often demands patient hospitalization.[1]
The dipstick screening test was performed in emergency department, while samples destined for urinalysis and urine culture were kept refrigerated at 2 to 8°C and sent to the central laboratory within 8 hours of collection
Different from other studies reporting high variability in leukocyte esterase (LE) sensitivity and specificity,(2,27,28) the analysis of LE as a standalone parameter in this study suggested LE is more sensitive than nitrite (79% versus 27% sensitivity); still, it does not seem to be a good predictor of positive urine culture, given the low PPV (51%)
Summary
Urinary tract infection is one of the most common infections and often demands patient hospitalization.[1]. Urinary sediment analysis using microscopy or digital flow morphology (system that auto-identifies and processes tube specimens by mixing, sampling, and analyzing urine particles automatically) is complementary to the dipstick test and contributes to the diagnosis of urinary tract infection. This test depends on several factors which can impact test results, such as sample collection, storage and transportation conditions, and technical expertise for accurate classification of elements of urinary sediment.[6,7,8,9]
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