What lab tests are recommended for patients on Azathioprine (Imuran)?

Laboratory Monitoring for Patients on Azathioprine

Regular monitoring of complete blood count (CBC) and liver function tests (LFTs) is required for all patients on azathioprine therapy, with monitoring frequency of at least every 3 months once a patient is stable on a fixed dose. 1, 2

Pre-Treatment Laboratory Assessment

• TPMT (thiopurine methyltransferase) activity or genotyping should be checked prior to initiating therapy to guide dosing and identify patients at high risk for toxicity 2, 3
• Baseline CBC including platelet count is essential before starting treatment 2, 3
• Baseline LFTs should be performed before starting therapy 2, 1
• Consider screening for hepatitis B (HBsAg and anti-HBc) and hepatitis C in all patients prior to immunosuppression 1
• For women, ensure compliance with the national cervical screening program before initiating therapy 1
• Consider checking varicella zoster virus (VZV) serology in patients with uncertain history of chickenpox 1

Monitoring Schedule

• Monitor CBC and LFTs weekly for the first 4 weeks of therapy 2, 1
• Continue weekly monitoring until maintenance dose is achieved 2
• Return to weekly monitoring following any dose increase 2
• Once stable on a fixed dose, reduce monitoring frequency to a minimum of once every 3 months for the duration of therapy 1, 2

Specific Parameters to Monitor

• Complete Blood Count (CBC):

  • White blood cell count - leucopenia is the most common hematological adverse event 1, 4
  • Platelet count - thrombocytopenia may occur in isolation or with leucopenia 4
  • Hemoglobin - anemia can occur but is less common 1
  • Macrocytosis - a common finding that can be used to assess patient compliance 1, 2

• Liver Function Tests (LFTs):

  • Transaminases (ALT, AST) - can indicate hepatotoxicity 1, 5
  • Alkaline phosphatase (ALP) - decreasing levels may indicate successful treatment of the underlying condition 6
  • Bilirubin - important to monitor for hepatotoxicity 1

Important Considerations

• Myelosuppression can develop at any time during treatment (from 2 weeks to 11 years after starting) 4
• Hepatotoxicity may occur rapidly (within days) or after months to years of therapy 5, 7
• Patients on concurrent medications that affect myelopoiesis (e.g., co-trimoxazole) or hepatic function require more vigilant monitoring 3
• Patients receiving both azathioprine and allopurinol should have dose reduction of azathioprine to approximately 1/3 to 1/4 the usual dose 3

Patient Instructions

• Report immediately any evidence of infection, unexpected bruising or bleeding, or jaundice 2, 3
• Report any neurologic symptoms (headache, dizziness, numbness, tingling, or weakness) 2
• Check temperature frequently and report fever immediately 2
• Report signs of infection such as cough, aches, fever, chills, wounds with redness/discharge, burning with urination, nausea, vomiting, and diarrhea 2

Monitoring in Special Populations

• For patients with hepatic dysfunction, more frequent monitoring of blood counts and LFTs is advised 1
• For patients with renal impairment, consider more frequent monitoring as drug metabolism may be impaired 3
• For patients on multiple immunosuppressants, consider more intensive monitoring schedules 1