DIAGNOSTIC PERFORMANCE OF SOME URINE ASSA YS IN URINARY-TRACT INFECTION

Objectives. 1. To determine the value of pyuria and bacteriuria by hig h-power field (hpf) in centrifuged urine and of tests with reactive st rips for determining leukocyte estearase activity and nitrites in the diagnosis of urinary tract infection (UTI). 2. To establish the ideal cut-off point for these tests. Design. Comparative survey. Setting. Se cond level health care unit of the Institute Mexicano del Seguro Socia l. Patients and methods. A total of 105 patients were prospectively st udied, with or without urinary symptoms, seen in the emergency ward. M easurements. A clinical history and physical exploration was done in e ach patient. A urine sample was used for microscopic analysis for dete rmining leukocytes and bacteria using hpf microscopy; the urine leukoc ytes count was assayed as well as leukocyte estearase and nitrites usi ng reactive strips. All samples were subjected to urine culture. Urine samples were obtained using a Nelaton probe in 65% of the patients an d the rest using the midstream urination technique. Results. Forty pat ients (38%) were identified as UTI cases based on clinical and laborat ory criteria (urine culture and leukocyte count). The best cut-off poi nt for number of leukocytes was 8 per hpf and for bacteriuria it was 2 + per hpf and for leukocyte estearase it was 1+. The sensitivity, spec ificity and predictive values of the pyuria hpf, bacteriuria by hpf an d leukocyte estearase by reactive strip were comparable. The nitrites had a lower sensitivity than the other tests (p < 0.05). The negative predictive value of the nitrites was less than the microscopic bacteri uria (74% vs 85%, p = 0.005). The combination of positive tests in leu kocytes and bacteriuria increased the specificity and the positive pre dictive value (99% and 96% respectively) when compared to the individu al tests. Conclusions. The diagnostic performance of leukocyte esteara se by reactive strips was similar to the microscopy of leukocytes and bacteria but the nitrite test had a lower performance. The combination of the leukocytes and bacteriuria measured by hpf appears to be very useful in the diagnosis of UTI.