What are the effects of azo compounds on the human body?

Effects of AZO Compounds on Urinalysis Results

AZO compounds can cause false positive results in urinalysis by turning urine orange-red, potentially interfering with colorimetric test strips and masking true clinical findings. 1

Mechanism of Interference

AZO compounds are synthetic chemicals containing the characteristic azo bond (-N=N-) that are widely used in:

• Medications (particularly urinary analgesics like phenazopyridine)
• Dyes for textiles, food, and industrial applications
• Laboratory preservatives

When these compounds enter the body, they undergo metabolism that affects urinalysis in several ways:

1. Color change: AZO compounds and their metabolites produce an orange to bright red coloration in urine 1
2. Colorimetric interference: The pigmentation can interfere with dipstick readings that rely on color changes
3. pH alterations: Some AZO compounds can affect urinary pH measurements

Clinical Impact on Urinalysis Parameters

Parameter	Effect of AZO	Clinical Significance
Color	Orange to bright red	May mask true urine color changes from hematuria
Nitrites	Potential false positive	May lead to incorrect diagnosis of UTI
Leukocyte esterase	Potential masking	May hide evidence of infection
Protein	Potential interference	May affect protein measurements
Glucose	Minimal interference	Generally reliable despite AZO presence

Common Sources of AZO Exposure

The most common source of AZO interference in clinical settings is phenazopyridine (Pyridium), a urinary analgesic that contains azo compounds and is used to treat urinary tract discomfort 1. Other sources include:

• Certain antibacterial medications
• Food dyes (particularly tartrazine)
• Textile dyes that may leach onto skin 2

Health Implications

Beyond urinalysis interference, AZO compounds have important health implications:

• Metabolic transformation: Intestinal bacteria can reduce AZO bonds, generating potentially toxic aromatic amines 3, 4
• Toxicity concerns: Some AZO metabolites have been associated with:
  • Contact allergies
  • Potential carcinogenicity (particularly those that release benzidine upon metabolism) 2
  • Liver problems if ingested in large quantities 5

Clinical Management

When interpreting urinalysis results in patients taking AZO-containing medications:

• Document all medications containing AZO compounds in the patient's history
• Consider postponing non-urgent urinalysis until 24-48 hours after discontinuation of AZO medications
• For urgent testing, use methods less affected by color interference (e.g., microscopic examination)
• Consider alternative testing methods when AZO interference cannot be avoided

Special Considerations

• Sodium azide poisoning: While rare, sodium azide (a different azide compound) can cause serious toxicity including hypotension, loss of consciousness, metabolic acidosis, and death 1
• Laboratory safety: Sodium azide is sometimes used as a laboratory preservative and can pose risks if improperly handled 1

Conclusion

Understanding the impact of AZO compounds on urinalysis is essential for accurate clinical interpretation. When AZO interference is suspected, clinicians should consider the timing of medication use, alternative testing methods, and the potential need to repeat testing after AZO compounds have cleared from the system.