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Is there a link between hyperbilirubinemia and elevated urine nitrite.

Susan Watts¹, David Bryan, Keith Marill

¹Department of Emergency Medicine, Texas Tech University Health Sciences Center, El Paso, TX 79905, USA. susan.watts@ttuhsc.edu

The American Journal of Emergency Medicine

|December 13, 2006

Summary

Hyperbilirubinemia significantly reduces the accuracy of urine nitrite tests for diagnosing urinary tract infections (UTIs). Elevated bilirubin levels increase false positive results, meaning a positive nitrite test is less likely to indicate a UTI in jaundiced patients.

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Area of Science:

Clinical Chemistry
Diagnostic Accuracy
Urology

Background:

The urine nitrite test is a rapid screening tool for urinary tract infections (UTIs).
Hyperbilirubinemia, a condition characterized by elevated bilirubin levels, can affect various physiological processes.
The impact of hyperbilirubinemia on the diagnostic performance of the urine nitrite test for UTIs remains unclear.

Purpose of the Study:

To investigate the influence of varying total serum bilirubin levels on the association between positive urine nitrite tests and positive urine cultures.
To determine if hyperbilirubinemia alters the specificity and sensitivity of the urine nitrite test in diagnosing UTIs.

Main Methods:

Retrospective review of 3,174 patient records including urinalysis, urine culture, and total serum bilirubin.
Patients categorized into three groups based on total serum bilirubin: <1.5 mg/dL, 1.5-3.0 mg/dL, and >3.0 mg/dL.
Calculated test characteristics (sensitivity, specificity, false-positive proportion) of the urine nitrite test across bilirubin ranges.

Main Results:

Specificity of the urine nitrite test significantly decreased with increasing total serum bilirubin (0.974 to 0.855, P < .0001).
Sensitivity showed no significant trend (P = .55).
The false-positive proportion increased dramatically with elevated bilirubin (17.5% to 72.0%, P < .0001), indicating a 4-fold higher likelihood of false positives in jaundiced patients.

Conclusions:

Increasing serum bilirubin levels significantly reduce the specificity of the urine nitrite test for UTI diagnosis.
A positive urine nitrite test in patients with hyperbilirubinemia, particularly jaundice, is often a false positive and may not indicate an actual UTI.