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Autoantibody Testing Strategy — SCE Rheumatology MCQ

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ModerateAutoimmune SerologyAutoantibody Testing StrategySCE Rheumatology

A 48-year-old woman is referred with 8 months of fatigue and widespread non-inflammatory musculoskeletal pain. There is no synovitis, photosensitive rash, oral ulceration, Raynaud phenomenon, sicca symptoms or objective muscle weakness. Full blood count, renal function, complement, CRP, ESR and urinalysis are all normal. An ANA requested by her GP is positive at 1:80 with a speckled pattern. Which principle should determine whether an extractable nuclear antigen (ENA) antibody panel is requested?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Request ENA when clinical features give a reasonable pre-test probability of connective tissue disease

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

E is correct: UK laboratory and referral guidance directs ANA and ENA testing by clinical suspicion of an ANA-associated connective tissue disease, not by an isolated serological result. ANA is sensitive but poorly specific, and low-titre positivity (1:80) occurs in 10–15% of healthy people, so in this woman with non-specific fatigue and pain, normal inflammatory markers, complement and urinalysis, an ENA panel has very low positive predictive value and risks incidental antibodies, further investigation and anxiety. B is wrong because reflex panels on every positive ANA generate false positives; C and D substitute an arbitrary titre threshold for clinical reasoning — high titre alone does not mandate ENA, and genuine anti-Ro or anti-Jo-1 disease can occur with modest titres. A delays nothing useful, since ANA positivity commonly persists in healthy individuals.

Reference: NHS North Central London ICB, "Right Test Right Time: Diagnostic blood test resource", section on ANA and anti-ENA testing (current). https://gps.northcentrallondon.icb.nhs.uk/right-test-right-time