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Septic Arthritis Biologics — SCE Rheumatology MCQ

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HardRheumatology EmergenciesSeptic Arthritis BiologicsSCE Rheumatology

A clinically quiescent patient with SLE has C4 persistently around half the lower reference limit over ten years, normal C3, stable anti-dsDNA and no renal or haematological activity. What is the best interpretation?

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Correct answer: C — Constitutional C4 deficiency may explain the baseline; follow within-person disease trends

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

E is correct. BSR notes that some patients carry a C4 null allele and maintain C4 at roughly half normal without active lupus. The long, isolated and clinically quiescent pattern supports a constitutional baseline rather than automatic escalation. C4 can still fluctuate with disease activity, so the result is not discarded: it is interpreted alongside the patient’s prior values, C3, anti-dsDNA, urine, blood count and symptoms. A single low component neither proves nephritis nor provides a glucocorticoid target.

Reference: BSR guideline for adult systemic lupus erythematosus: https://academic.oup.com/rheumatology/article/57/1/e1/4318863