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Baseline Pre-DMARD Assessment — SCE Rheumatology MCQ

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EasyRheumatology PharmacologyBaseline Pre-DMARD AssessmentSCE Rheumatology

A 50-year-old man with seropositive rheumatoid arthritis has been intolerant of both methotrexate and sulfasalazine, and his rheumatologist plans to start azathioprine before transferring monitoring to shared care. Baseline weight, full blood count, renal function, ALT, AST and albumin are normal, blood pressure is 124/78 mmHg, and screening for hepatitis B, hepatitis C and HIV is negative. He has no tuberculosis risk factors. Which additional baseline investigation is most important before this drug is prescribed?

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Correct answer: B — Thiopurine methyltransferase (TPMT) activity

Explanation lettering: C = shown as B · E = shown as C · B = shown as E

C is correct. Azathioprine is a thiopurine, so TPMT status must be known before prescribing: absent activity contraindicates thiopurines because of the risk of profound myelosuppression, reduced activity requires specialist supervision, and intermediate (heterozygous) activity requires a lower maintenance dose. The universal baseline panel (weight, FBC, renal function, transaminases, albumin) and adult viral screening for HBV, HCV and HIV are already complete, and latent tuberculosis testing is risk-stratified, not universal, so none of these adds discrimination here. Serum magnesium (A), ECG and blood pressure (B) and HbA1c/lipids (D) are baseline requirements for calcineurin inhibitors such as ciclosporin and tacrolimus, not azathioprine. Retinal assessment (E) relates to hydroxychloroquine retinopathy surveillance.

Reference: NHS Specialist Pharmacy Service. Azathioprine monitoring (pre-treatment TPMT assessment; aligned to the 2025 British Society for Rheumatology csDMARD prescription and monitoring guideline), 2025. https://sps.nhs.uk/monitorings/azathioprine-monitoring/