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Original Study: Should Nitrofurantoin Be Used to Treat Alkaline Urinary Tract Infection?

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Our analysis of 1,331 adult patients who were diagnosed with a urinary tract infection (UTI) in the ED found that 90% (n = 1,194/1,331) had a urine pH between 5.0 and 7.0. The majority of these UTIs were caused by Escherichia coli. In addition, we noted that Proteus mirabilis, which is intrinsically resistant to nitrofurantoin, was the most common cause of UTI in patients who had a urine pH was over 8.5.




Urinary tract infections (UTIs), one of the most common human bacterial infections, affect approximately 150 million people annually worldwide.1,2 In the United States, UTIs account for approximately 1% of all outpatient clinic visits and about 2 to 3 million ED visits annually.1,3-5

Although the urine pH level is frequently assessed in urinalysis, it is rarely considered in the management of a patient with a UTI.

Reports correlating urine pH with urine culture data from ED patients with UTIs are lacking. While poorly studied, there are multiple factors that could potentially alter the urine pH of patients with a UTI, including blood pH, diabetes, dehydration, ketosis, drugs, and renal function, as well as factors related to the infecting microorganism. For instance, Proteus mirabilis produces urease, an enzyme that hydrolyzes urea to ammonia and carbon dioxide.6-8


The objective of this study is to assess the relationship between the urine pH and the infecting microbe in ED patients diagnosed with UTIs, and to determine if P mirabilis is associated with alkaline urine.


We obtained approval from our Institutional Review Board to retrospectively obtain electronic medical record data from patients aged 18 years and older who presented to our institution’s ED and who were diagnosed with either cystitis or a UTI between January 1, 2012 and March 31, 2015. Both urine pH level and a urine culture were obtained for all patients.

The results of all of the patients’ urinary cultures in our study were positive for one bacterial species or genera (≥100,000 CFU/mL). The International Classification of Disease, Ninth Revision/Tenth Revision codes used to identify patients with cystitis and UTI were as follows: 595.0, 595.1, 595.9, 599.0, N30.91, N30.90, N30.80, N30.81, N30.00, N30.01, N30.20, N30.20, and N39.0.

To ensure that the focus of our study was limited to cystitis and UTIs, we excluded patients who were diagnosed with pyelonephritis, sexually transmitted infection, pelvic inflammatory disease, or vaginal discharge. The urine pH values reported from the clinical laboratory were 5.0, 5.5, 6.0, 6.5, 7.0. 7.5, 8.0, 8.5, and 9.0. Our dataset contained 1,331 clinical encounters. We used descriptive statistics and unpaired t-tests to evaluate the associations between urine pH values and the different microbes.

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