From the Research
Yes, azo (phenazopyridine) can alter urinary test results. This over-the-counter medication, commonly used to relieve urinary pain and discomfort, contains an orange dye that significantly colors the urine and can interfere with various urinalysis tests. Specifically, azo can affect dipstick urinalysis results for glucose, protein, ketones, bilirubin, and urobilinogen by creating false positive or negative readings. The medication's orange-red coloration can also interfere with visual color-based tests and automated analyzer readings.
Key Points to Consider
- If you need to undergo urinary testing, you should inform your healthcare provider about any azo use, as it's generally recommended to stop taking phenazopyridine 24-48 hours before scheduled urinalysis tests.
- The interference occurs because phenazopyridine is metabolized in the body and excreted through the kidneys, with approximately 65% of the drug appearing in urine as unchanged compound and metabolites that create the distinctive orange-red color.
- This coloration and chemical properties directly impact the chemical reactions used in urinalysis testing methods, as noted in studies such as 1 which evaluated the efficiency and safety of phenazopyridine for the treatment of uncomplicated urinary tract infection.
Clinical Implications
- Phenazopyridine can be effective in assessing ureteral patency when used preoperatively, as seen in a study published in 2, where it was effective in more than 90% of cases.
- However, its use should be carefully considered in the context of urinary testing due to its potential to alter test results.
- The most recent and highest quality study, 2, highlights the importance of considering the dose and timing of phenazopyridine administration, as well as patient factors such as renal function and intraoperative urine output, when assessing its effectiveness and potential impact on urinary test results.