Can Azo (phenazopyridine) cause glucose to appear in urine?

Can Azo (Phenazopyridine) Cause Glucose in Urine?

No, Azo (phenazopyridine) does not cause glucose to appear in urine tests when using modern glucose oxidase (GO) or glucose dehydrogenase (GDH) based testing methods. 1

Understanding Urinalysis Glucose Testing

• Modern urinalysis for glucose primarily uses glucose oxidase (GO) or glucose dehydrogenase (GDH) based methods, which have replaced older copper-reduction methods due to their higher specificity 1, 2
• These enzymatic methods are specific for glucose and are not affected by phenazopyridine (Azo) 1
• Semiquantitative test strips using glucose oxidase reactions are the recommended method for detecting glucose in urine 2

Known Interfering Substances with Glucose Testing

• Documented substances that can interfere with glucose testing include:
  • Ascorbic acid (vitamin C) - can cause false negative glucose results 1, 3
  • Beta-lactam antibiotics (cephalosporins and penicillins) 3
  • Levodopa and salicylates 3
• Phenazopyridine is not listed among substances that interfere with modern glucose oxidase-based urine glucose tests 1, 3

Phenazopyridine (Azo) Properties and Metabolism

• Phenazopyridine is an azo dye used as a urinary analgesic that colors the urine orange-red 4, 5
• It is extensively metabolized in humans, with 5-hydroxyl PAP being the major metabolite (48.3% of the dose) 5
• While phenazopyridine can interfere with some urine tests due to its color, it does not affect glucose oxidase-based testing methods 1, 3

Clinical Implications

• For patients taking phenazopyridine:
  • The orange-red coloration of urine may affect visual interpretation of dipstick tests that rely on color changes 4
  • However, this coloration does not chemically interfere with the glucose oxidase reaction used in modern glucose testing 1, 3
• For accurate glucose monitoring in patients with diabetes:
  • Self-monitoring of blood glucose (SMBG) is preferred over urine glucose testing due to inherent limitations of urine testing 2
  • Urine glucose testing provides no information about blood glucose concentrations below the renal threshold (approximately 180 mg/dL) 2

Important Considerations

• If a patient taking phenazopyridine shows unexpected glucose in urine:
  • Consider other causes of glycosuria, as the finding is not related to phenazopyridine use 1
  • Evaluate for diabetes mellitus, renal tubular disorders, or other conditions that may cause glycosuria 2
• When interpreting multiple parameters on urinalysis in patients taking phenazopyridine, consider the clinical context rather than interpreting findings in isolation 1