Do Azo (phenazopyridine) or Pyridium (phenazopyridine) affect urine dipstick results?

Phenazopyridine (AZO/Pyridium) Effects on Urine Dipstick Results

Yes, phenazopyridine (AZO/Pyridium) significantly interferes with urine dipstick testing, causing false-positive results for some parameters and potentially masking others due to its orange-red coloration of urine. 1

Key Interferences with Urine Dipstick Testing

Confirmed Interferences

• Color-based reactions: Phenazopyridine is an azo dye that interferes with urinalysis based on spectrometry or color reactions 1
• Glucose testing: Can produce false-negative results with glucose oxidase methods 2
• Leukocyte esterase and nitrite tests: The orange-red discoloration can make visual interpretation of color changes difficult
• Hematuria detection: The red-orange coloration can mask or mimic blood in the urine

Clinical Implications

1. Diagnostic confusion: May lead to misdiagnosis or missed diagnosis of urinary tract infections
2. UTI monitoring challenges: Can interfere with assessment of treatment response
3. False positives: May trigger unnecessary additional testing or treatment

Recommendations for Clinical Practice

When Evaluating Patients on Phenazopyridine

1. Document medication use: Always note phenazopyridine use when interpreting urinalysis results
2. Consider timing:
   • Phenazopyridine effects on urine can persist for 24-48 hours after discontinuation
   • If possible, collect urine samples before starting phenazopyridine or after a washout period

For Accurate Urinalysis

1. When dipstick testing is necessary:

   • Consider temporarily discontinuing phenazopyridine if clinically appropriate
   • Document the medication's presence when interpreting results
   • Use microscopic examination rather than dipstick alone when assessing for pyuria or bacteriuria 3

2. For UTI diagnosis in patients on phenazopyridine:

   • Rely on microscopic examination of urine sediment for WBCs and bacteria 3
   • Consider urine culture for definitive diagnosis 3
   • Remember that the presence of both leukocyte esterase and nitrite has high specificity (96%) for UTI when visible 3

Special Considerations

Patient Education

• Inform patients that phenazopyridine causes reddish-orange discoloration of urine 1
• Advise that it may stain fabric and contact lenses 1
• Explain that this medication is for symptomatic relief only and does not treat the underlying infection

Duration of Use

• Limit use to 2 days when used with an antibiotic for UTI symptoms
• Prolonged use may mask persistent symptoms requiring medical attention
• Extended use increases risk of adverse effects including skin/sclera yellowing (indicating accumulation) 1

Pitfalls to Avoid

1. Don't rely solely on dipstick testing when patients are taking phenazopyridine
2. Don't assume persistent orange urine is just from the medication - it could indicate impaired renal excretion requiring discontinuation 1
3. Don't use phenazopyridine as a diagnostic tool - while it can stain pads in cases of incontinence, it has a high false-positive rate even in continent individuals 4
4. Don't forget to consider drug interactions when interpreting any laboratory test results in patients taking multiple medications

By understanding these interferences and taking appropriate precautions, clinicians can avoid diagnostic errors and ensure appropriate management of patients taking phenazopyridine while still obtaining accurate urinalysis results.