The Predictability of Urinary Pathogens Based on the Urinalysis Nitrite Test in Hospitalized Patients

Abstract

Purpose Some urinary tract pathogens are capable of reducing nitrates to nitrites, including Escherichia coli, Klebsiella, Proteus, and Serratia. A urinalysis (UA) is commonly performed in patients with symptoms of a urinary tract infection (UTI) in order to detect the presence of nitrites in the urine. The objectives of this study were: 1) to assess the predictive value of the nitrite test in distinguishing nitrate-reducing pathogens from non-reducing pathogens; 2) to determine whether the results of the nitrite test can predict the susceptibility of the urine pathogen to several common antibiotics. Methods A retrospective cross-sectional chart review identified inpatients who had a UA and a positive urine culture (UC). Patients were divided into nitrite-positive and -negative groups based on UA results. Urine pathogens were identified by culture and antibiotic susceptibilities and were compared within the groups. Results Eighty-six UAs were included. A nitrite-positive UA had a 90.6% positive predictive value in identifying a nitrite-producing pathogen. A nitrite-negative UA had a negative predictive value of 33.3% in identifying a non-nitrite producing pathogen. There was no difference in the antibiotic susceptibility for ampicillin, gatifloxacin, and trimethoprim/sulfamethoxazole between the groups. Conclusions A nitrite-positive result indicates a high likelihood of the presence of a nitrite-producing organism. However, a negative nitrite test is a poor predictor of the absence of nitrite-producing pathogens. Therefore, patients with a positive nitrite test on UA can be treated empirically for a nitrite-producing organism until confirmatory laboratory studies can be completed. A nitrite-negative UA is not useful in ruling out a nitrate-reducing organism.