Antinuclear Antibodies (ANA)

ANA detects antibodies that bind structures inside the cell nucleus. It's the entry-point screen for systemic autoimmune diseases that target the body's own DNA and nuclear proteins. The result has two parts: a titer (1:40, 1:80, 1:160, 1:320, etc., indicating how dilute the serum can be before the signal disappears) and a pattern (homogeneous, speckled, nucleolar, centromeric — each loosely associated with different diseases). Crucial: ANA positivity alone is NOT a diagnosis — up to 15% of healthy adults and 30% of elderly women have low-titer positive ANA without any autoimmune disease. The test earns clinical weight only when interpreted with symptoms.

• High titer (>1:320) + symptoms — strongly suggests systemic lupus erythematosus (SLE), scleroderma, mixed connective tissue disease.
• Homogeneous pattern — typical of drug-induced lupus and SLE.
• Speckled pattern — mixed CTD, Sjögren's, scleroderma.
• Centromeric pattern — limited scleroderma (CREST).
• Nucleolar pattern — diffuse scleroderma.
• Drug-induced (hydralazine, procainamide, isoniazid, anti-TNF) — usually homogeneous.

• Negative ANA — makes systemic autoimmune disease unlikely (though not impossible — some scleroderma patients are ANA-negative).
• Low-titer (<1:160) without symptoms — common in healthy people, especially women and elderly; clinically irrelevant.