From the FDA Drug Label
Laboratory Test Interaction: Due to its properties as an azo dye, Phenazopyridine HCl may interfere with urinalysis based on spectrometry or color reactions. The Phenazopyridine HCl may cause false positives for certain urine tests due to its properties as an azo dye, but it does not explicitly state that it causes false positives for nitrites and leukocyte esterase.
- The drug label warns of potential interference with urinalysis based on spectrometry or color reactions, which could imply potential false positives for certain tests.
- However, without explicit information on nitrites and leukocyte esterase, a conclusion cannot be drawn 1.
From the Research
Yes, AZO (Phenazopyridine) can cause false positives for nitrites in urine tests but does not typically affect leukocyte esterase results. Phenazopyridine is an azo dye that turns urine orange-red and can interfere with colorimetric test strips used to detect nitrites, potentially leading to inaccurate results. This happens because the medication's strong coloration can mask or alter the color change that indicates the presence of nitrites on the test strip. However, the leukocyte esterase test works through a different chemical reaction that is generally not affected by phenazopyridine. If you're taking AZO and need accurate urinalysis results, you should inform your healthcare provider about your medication use before the test. They may recommend temporarily stopping the medication 24-48 hours before testing or may use alternative testing methods that aren't affected by the dye. This interference occurs because phenazopyridine is specifically designed to concentrate in the urinary tract, where it exerts its local analgesic effect while also producing its characteristic urine discoloration.
Some key points to consider:
- The sensitivity and specificity of urine tests can be affected by various factors, including the presence of certain medications like AZO 2.
- The combination of nitrite and leukocyte esterase tests can provide a more accurate diagnosis of urinary tract infections than either test alone 3.
- Leukocyte esterase testing has been shown to be a valuable screening test for detecting urinary tract infections, with high sensitivity and moderate specificity 4.
- However, the provided studies do not directly address the effect of AZO on urine test results, but the mechanism of action of phenazopyridine and its potential to interfere with colorimetric tests is well understood.
Given the potential for AZO to interfere with nitrite testing, it is essential to inform healthcare providers about AZO use before undergoing urinalysis to ensure accurate test results and appropriate diagnosis and treatment.