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SLE Serological Activity — RACP Adult Medicine MCQ

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ModerateRheumatologySLE Serological ActivityRACP Adult Medicine

A 25-year-old woman with SLE presents with active nephritis (rising creatinine, proteinuria 3 g/day). Anti-dsDNA is strongly positive (titre rising from 50 to 200 IU/mL). C3 is 0.35 g/L (low, normal 0.9-1.8), C4 is 0.05 g/L (very low). ESR is 55 mm/hr but CRP is only 8 mg/L. What laboratory pattern best indicates active lupus nephritis?

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Correct answer: D — Rising anti-dsDNA with falling complement (C3 and C4)

Rising anti-dsDNA titres with falling complement (C3 and C4) is the classic serological pattern of active SLE, particularly lupus nephritis. Anti-dsDNA is consumed in immune complex formation, and complement is consumed during immune complex clearance. CRP is characteristically low/normal in SLE flares (unlike infection). ESR is elevated but non-specific. The CRP-ESR dissociation (high ESR, low CRP) is a classic SLE feature.

Reference: EULAR – 2024 – SLE Monitoring; eTG Rheumatology 2024