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Falling MCV on Methotrexate — SCE Rheumatology MCQ

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HardAutoimmune SerologyFalling MCV on MethotrexateSCE Rheumatology

A patient taking methotrexate 15 mg weekly has an MCV of 103 fL, unchanged for six months. Haemoglobin, neutrophils, platelets, liver tests, B12, folate and TSH are normal, and there are no clinical toxicity features. What is the best response under current BSR guidance?

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Reveal the answer and explanation

Correct answer: C — Continue methotrexate with routine trends; stable isolated macrocytosis is not an interruption threshold

Explanation lettering: E = shown as A · D = shown as C · A = shown as D · C = shown as E

D is correct. The 2025 BSR csDMARD guideline removed MCV as an isolated action threshold. With stable mild macrocytosis, normal counts and exclusion of common reversible causes, methotrexate can continue while trends and the whole blood count are monitored. A applies an obsolete automatic cutoff and overstates prediction of marrow failure. B changes folate dosing for a cosmetic laboratory endpoint and may conflict with the agreed methotrexate schedule. C is disproportionate without cytopenia, dysplasia or progressive unexplained change. E confuses a red-cell index with inefficacy. A new rising MCV still warrants clinical review for alcohol, liver disease, thyroid disease, haematinic deficiency and evolving marrow disorder; “continue” does not mean ignore context.

Reference: 2025 BSR guideline for prescription and monitoring of conventional synthetic DMARDs: https://academic.oup.com/rheumatology/article/65/2/keaf522/8322743