Medical Emergencies · patient case question
Which serological test is used as the initial screen when an autoimmune connective tissue disease is suspected?
Patient case: Rheumatoid arthritis managed with adalimumab and methotrexate
Patient: Female, 55 years old
Chief Complaint: “I need a crown replaced and my hands make brushing hard.”
Background: Rheumatoid arthritis of eight years' duration. Adalimumab (Humira) every other week and weekly oral methotrexate with folate supplementation. No other medications.
Vital Signs: BP 122/78 mmHg · HR 74 bpm · T 98.1°F
Findings: Symmetric swelling of the metacarpophalangeal and proximal interphalangeal joints with reduced grip strength. Limited mouth opening, 32 mm. Bilateral TMJ crepitus. Generalized plaque accumulation.
Show answer and explanation
Correct answer: C. Antinuclear antibody (ANA) test
- A. Serum uric acid is the test for gout and hyperuricaemia, unrelated to connective tissue autoimmunity.
- B. The ESR rises in any inflammatory state, infection or malignancy. It measures activity, not aetiology, and points to nothing in particular.
- C. CORRECT. The ANTINUCLEAR ANTIBODY test detects autoantibodies against nuclear constituents and is the standard first-line SCREEN for autoimmune connective tissue disease. Its value is largely in its NEGATIVE predictive power — a negative ANA makes systemic lupus erythematosus very unlikely. A positive result is then refined by pattern and by specific antibodies: anti-dsDNA and anti-Sm for lupus, anti-Ro/SSA and anti-La/SSB for Sjögren syndrome, anti-centromere and anti-Scl-70 for systemic sclerosis. Note that ANA is positive in up to 15% of healthy people, so it must be interpreted with the clinical picture.
- D. CRP is an acute-phase reactant. Like the ESR it tracks inflammatory activity without identifying its cause.
Note: For rheumatoid arthritis specifically the more useful pair is RHEUMATOID FACTOR plus ANTI-CCP — anti-CCP being far the more specific and an early predictor of erosive disease. ANA is the broad screen across the connective tissue diseases; anti-CCP is the RA-specific one. Dentally, Sjögren syndrome is the overlap to watch for, since secondary Sjögren accompanies RA and brings xerostomia with rampant cervical caries.
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