Impact of Phenazopyridine (Pyridium) on Urinalysis Results
Yes, phenazopyridine (Pyridium) significantly alters urinalysis results by causing orange-red discoloration of urine and potentially interfering with various urinalysis test parameters.
How Phenazopyridine Affects Urinalysis
Direct Discoloration Effects
- Produces a distinctive reddish-orange discoloration of urine that can persist throughout treatment
- May stain fabrics and even contact lenses 1
- The color change begins shortly after ingestion and can last for hours to days depending on dosage
Laboratory Test Interference
- Spectrophotometric interference: Phenazopyridine interferes with urinalysis tests based on spectrometry or color reactions due to its properties as an azo dye 1
- May cause false results in the following urinalysis parameters:
- Dipstick tests for glucose, protein, ketones, bilirubin, and urobilinogen
- Tests that rely on color change endpoints
- Automated urinalysis systems that use spectrophotometric methods
Clinical Implications
Diagnostic Challenges
- May mask or mimic hematuria due to the orange-red coloration
- Can lead to misinterpretation of dipstick results for urinary tract infections
- Has been used deliberately as a diagnostic tool in specialized tests like the Pyridium pad test for urinary incontinence, where its staining properties help identify urine leakage 2
Recommendations for Clinical Practice
- Temporarily discontinue phenazopyridine before collecting urine samples for diagnostic testing whenever possible
- If urinalysis must be performed while patient is taking phenazopyridine:
- Document medication use clearly on laboratory requisitions
- Consider microscopic examination rather than relying solely on dipstick results
- Be aware that the medication may interfere with automated urinalysis systems
Patient Education Points
- Inform patients that their urine will turn reddish-orange while taking this medication 1
- Advise that this discoloration is expected and not harmful
- Warn that it may stain clothing or other fabrics
- Instruct patients to notify healthcare providers about phenazopyridine use before any urinalysis
Safety Considerations
Monitoring Requirements
- A yellowish tinge of the skin or sclera may indicate accumulation due to impaired renal excretion and necessitate discontinuation 1
- Patients with decreased renal function, especially elderly patients, require careful monitoring
- Extended use should be avoided as phenazopyridine is intended for short-term symptomatic relief only
Potential Adverse Effects
- In rare cases, phenazopyridine can cause serious adverse effects including:
By understanding these effects on urinalysis, clinicians can avoid misinterpretation of test results and ensure accurate diagnosis and treatment of urinary conditions in patients taking phenazopyridine.