Detection of urinary tract infections by reduction of nitroblue tetrazolium: Technical Note

Abstract

Nitroblue tetrazolium (NBT) reduction to formazan has been used as a marker for nitric oxide synthase (NOS). Since inducible NOS activity is elevated in urine from patients with urinary tract infections (UTIs), we investigated the accuracy of NBT reduction as an early predictor of UTIs and quantified the relationship between inducible NOS and NBT. Urine samples from 434 patients were screened for the presence of UTIs with leukocyte-esterase and nitrite dipsticks and with NBT reduction. The rapid screening results from each test were compared to urine culture results. In addition, NBT reduction parameters were measured in urine pellet at 595 nm after incubation with one of four factors: NOS cofactors, NOS inhibitors, NADH, or superoxide dismutase/catalase. As a urine screening test for UTIs, NBT reduction was more sensitive with a higher negative predictive accuracy than the nitrite dipstick. NBT reduction also was more specific with a higher positive predictive accuracy and negative predictive accuracy than the leukocyte-esterase dipstick. In infected urine pellet, both NADPH, a NOS cofactor, and NADH increased NBT reduction. Superoxide dismutase/catalase decreased NBT reduction. Although NOS may not be the only NBT reducing enzyme, rapid, visible reduction of NBT is induced in urine from patients with UTIs.