Utility of nitrate and leukocyte esterase tests for laboratory detection of urinary tract infection in a general population at the Philippine Heart Center: A prospective study.

RATIONALE: Urinary Tract Infection (UTI) requires costly urine culture to confirm the diagnosis. Dipstick test as part of urinalysis is used widely to screen for UTI. Nitrite test (NT) and leukocyte esterase (LE) test included in the Dipstick indirectly detect UTI. Various studies on the diagnostic value of these two tests were done on different settings and different populations, but with conflicting results.

OBJECTIVE: To compare NT and LE test and the combination of both using urine culture as reference standard in the laboratory detection of UTI in our own setting.

METHODS: Urine specimens from the Philippine Heart Center general patient population with requests for urinalysis and uroculture were included in this cohort study. One portion of each specimen was plated on Blood Agar Plate and MacConkey Agar and the other portion was subjected to urinalysis in which Dipstick (Roche Combur test10 UX, Roche Miditron M) NT and LE tests were included. The urine culture is followed up after 48 hours. The NT, LE results and the combination of both were compared to the culture results.

RESULTS: Of the three hundred twenty four (324) specimens, 100 (30.86 percent) have significant growth in uroculture. The most frequent isolate is Escherichia coli (37 percent). The results are significant (p=0.000) with 95 percent confidence interval. The LE test shows 39.5 percent sensitivity, 82.2 percent specificity, 77.0 percent predictive value positive (PPV), and 47.3 percent predictive value negative (NPV). The NT shows 78.6 percent sensitivity, 73.3 percent specificity, 21.8 percent PPV, and 97.3 percent NPV. Combined NT-LE test shows 76.0 percent sensitivity, 82.5 percent specificity, 46.3 percent PPV, and 94.5 percent NPV.

CONCLUSION: Although NT, LT test or a combination of both show low specificity, sensitivity and PPV to allow their use as screening tests for UTI, the high NPV of NT and the combined negative of both tests maybe used to rule out UTI. Patients with negative NT test or combined negative NT and LE test can be reasonably excluded from the need for urine culture.