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.
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