Pre-Azathioprine Testing Requirements for Crohn's Disease Patients

Essential Baseline Tests

The British Journal of Dermatology recommends TPMT activity testing, complete blood count, liver function tests, and renal function tests must be performed prior to initiating azathioprine therapy in a patient with Crohn's disease 1, 2
TPMT activity should be checked in all patients prior to receiving azathioprine, with a strength of recommendation A and level of evidence 1+ 1, 2
TPMT genotyping is only required for patients with indeterminate phenotype or those who have had a recent blood transfusion 1
Full blood count with differential white cell count should be obtained as baseline 1, 2
Patients with pre-existing cytopenias may require dose adjustments or consideration of alternative therapy 3
Liver blood tests including transaminases must be performed, as azathioprine can cause hepatotoxicity 1, 2
Severe hepatic impairment is a contraindication to azathioprine use 1
Baseline renal function should be assessed, with patients with renal impairment requiring dose reduction 1, 2

Consider screening for severe infections, as these are contraindications to azathioprine therapy 1
Viral hepatitis screening may be prudent as immunosuppression can lead to reactivation of hepatitis B virus 1
Pregnancy testing should be considered in women of childbearing age, as pregnancy is a relative contraindication 1, 4
Women should be advised to avoid pregnancy during treatment with azathioprine 4

Liver function tests should be monitored regularly, with similar frequency to blood counts 4
Dose adjustments may be needed based on monitoring results and development of side effects 5

Failure to check TPMT activity can lead to severe myelosuppression in patients with TPMT deficiency 1, 2
Overlooking hepatotoxicity risk can lead to severe liver damage, and regular liver function monitoring is essential 4
Ignoring renal function can lead to inadequate dose adjustment, and doses should be adjusted in patients with renal impairment 1