Distribution of Test Results of a Hypothetical Leukocyte Esterase Test in a Cohort of 1000 Women With an Assumed 30% Prevalence of UTI
Results | Disease Present | Disease Absent | Total Patients |
|---|---|---|---|
Test positive | True positive (TP) 213 patients (71% of 300) | False positive (FP) 105 patients (700 −595) | 318 patients with a positive test |
Test negative | False negative (FN) 87 patients (300 −213) | True negative (TN) 595 patients (85% of 700) | 682 patients with a negative test |
Total patients | 300 patients with UTI (assumed) | 700 patients without UTI (assumed) | 1000 patients |
Positive predictive value (PPV) = TP/(all patients with a positive test) = TP/(TP + FP) = 213/(213 + 105) = 67%. Negative predictive value (NPV) = TN/(all patients with a negative test) = TN/(TN + FN) = 595/(595 + 87) = 87%. Positive likelihood ratio (LR+) = sensitivity/(1 − specificity) =0.71/(1 − 0.85) =4.73. Negative likelihood ratio (LR-) = (1 − sensitivity)/specificity = (1 − 0.71)/0.85 = 0.34. UTI = urinary tract infection | |||