Laboratory Monitoring for Patients on Azathioprine

Pre-Treatment Laboratory Assessment

The British Journal of Dermatology recommends checking thiopurine methyltransferase (TPMT) activity or genotyping prior to initiating azathioprine therapy to guide dosing and identify patients at high risk for toxicity 1, 2
Baseline complete blood count (CBC) including platelet count should be performed before starting azathioprine therapy 1
Baseline liver function tests (LFTs) should be performed before starting azathioprine therapy 1, 3
Consider hepatitis screening prior to treatment if using azathioprine with other hepatotoxic agents, as recommended by the Chest journal 4

The British Journal of Dermatology recommends weekly CBC and LFTs for the first 4 weeks of azathioprine therapy, then monthly until maintenance dose is achieved, followed by monitoring every 3 months for the duration of therapy 1, 5, 3
Continue weekly monitoring until maintenance dose is achieved 1, 3
Return to weekly monitoring following any dose increase 1
Once stable on a fixed dose, reduce monitoring to a minimum of once every 3 months for the duration of therapy, as recommended by the British Journal of Dermatology 5, 3

Macrocytosis is a common finding that can be used to assess patient compliance, according to the British Journal of Dermatology 5
Transaminases (ALT, AST) should be monitored, as recommended by the British Journal of Dermatology 1, 5
Alkaline phosphatase (ALP) levels may indicate successful treatment of the underlying condition, although this is based on a guideline from Praxis Medical Insights, an alternative source is needed for this fact, however the British Journal of Dermatology recommends monitoring bilirubin 5

Patients should report immediately any evidence of infection, unexpected bruising or bleeding, or jaundice, as recommended by the British Journal of Dermatology 1
Patients should report any neurologic symptoms (headache, dizziness, numbness, tingling, or weakness), as recommended by the Chest journal 4
Patients should check temperature frequently and report fever immediately, as recommended by the Chest journal 4
Patients should report signs of infection such as cough, aches, fever, chills, wounds with redness/discharge, burning with urination, nausea, vomiting, and diarrhea, as recommended by the Chest journal 4

The British Journal of Dermatology recommends baseline LFTs should be performed before starting therapy 6
Consider screening for hepatitis B (HBsAg and anti-HBc) and hepatitis C in all patients prior to immunosuppression, as recommended by the British Journal of Dermatology 7
For women, ensure compliance with the national cervical screening program before initiating therapy, according to the British Journal of Dermatology 7
Consider checking varicella zoster virus (VZV) serology in patients with uncertain history of chickenpox, as suggested by the British Journal of Dermatology 7

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, as recommended by the British Journal of Dermatology 6
Once stable on a fixed dose, reduce monitoring frequency to a minimum of once every 3 months for the duration of therapy, according to the British Journal of Dermatology 6

The British Journal of Dermatology notes that leucopenia is the most common hematological adverse event, and white blood cell count should be monitored 6
The British Journal of Dermatology recommends monitoring hemoglobin, as anemia can occur but is less common 6
Macrocytosis is a common finding that can be used to assess patient compliance, as stated by the British Journal of Dermatology 6
The British Journal of Dermatology suggests monitoring transaminases (ALT, AST) to indicate hepatotoxicity 6
Bilirubin should be monitored for hepatotoxicity, according to the British Journal of Dermatology 6

For patients with hepatic dysfunction, more frequent monitoring of blood counts and LFTs is advised, as recommended by the British Journal of Dermatology 7
For patients on multiple immunosuppressants, consider more intensive monitoring schedules, according to the British Journal of Dermatology 7

The British Association of Dermatologists recommends checking thiopurine methyltransferase (TPMT) activity through genotyping or phenotyping to identify patients at increased risk for severe myelotoxicity, with patients having absent TPMT activity (0.3% of population) at risk for life-threatening bone marrow failure 8, 9, 10, 11
Patients with intermediate TPMT activity (10% of population) require dose reduction to 1.0-1.5 mg/kg daily, according to the British Journal of Dermatology 9, 10, 11
The American Gastroenterological Association and British Association of Dermatologists note that TPMT testing identifies only a subset of at-risk patients, with 73% of patients who develop severe myelosuppression having normal TPMT activity, making regular blood count monitoring essential regardless of TPMT status 8, 9, 10

The American College of Gastroenterology and British Association of Dermatologists recommend weekly complete blood counts (CBC) including white blood cell count, neutrophil count, and platelet count for the first month, twice monthly for months 2-3, then monthly or more frequently if dose changes occur 8, 9
The British Journal of Dermatology suggests that this intensive monitoring catches early bone marrow suppression, which typically manifests first as leukopenia 9, 10

The American Association for the Study of Liver Diseases and British Association of Dermatologists recommend monitoring liver function tests on the same schedule as CBC, as hepatotoxicity can occur even after 1 year of therapy 8, 12
The European Association for the Study of the Liver notes that patients with cirrhosis commonly have baseline cytopenia from hypersplenism, which complicates interpretation but does not necessarily increase azathioprine-related marrow depression risk per se 8, 12

The European Association for the Study of the Liver recommends surveillance every 3 to 6 months during maintenance treatment for patients with autoimmune hepatitis on azathioprine monotherapy 13
The European Association for the Study of the Liver suggests monitoring transaminases and IgG levels to maintain stable remission in patients with autoimmune hepatitis on azathioprine monotherapy 13
The European Association for the Study of the Liver advises monitoring for cytopenias during long-term azathioprine maintenance treatment 13
Patients with autoimmune hepatitis require lifelong surveillance due to frequent flares and relapses even after complete remission, as recommended by the European Association for the Study of the Liver 13