If you've had blood tests for suspected autoimmune disease, the results can be confusing. The tests have unfamiliar names, the reference ranges aren't always intuitive, and a positive result can seem alarming when it might not be. This guide walks through each major test clearly.
Screening Tests
ANA (Antinuclear Antibody)
What it measures: Antibodies directed against the nucleus of cells, a broad screening marker for several autoimmune conditions.
Result format: Reported as a titre (e.g., 1:80, 1:160, 1:320) and a pattern (e.g., speckled, homogeneous).
Positive in: Lupus, Sjögren's, systemic sclerosis, MCTD, and many others, but also in 13–15% of healthy people.
Key caveat: A positive ANA alone is not a diagnosis. It needs to be interpreted alongside symptoms and other tests.
ESR (Erythrocyte Sedimentation Rate)
What it measures: How quickly red blood cells settle in a tube, a non-specific marker of inflammation.
Result format: mm/hr. Normal is typically under 20 mm/hr in young adults; rises with age.
Elevated in: Active inflammatory or autoimmune disease, infection, malignancy, and others. Not specific to any one cause.
Key caveat: ESR rises slowly and falls slowly. It reflects average inflammation over days to weeks. It can be normal even with active disease in some cases.
CRP (C-Reactive Protein)
What it measures: A protein produced by the liver in response to inflammation, rises and falls faster than ESR.
Result format: mg/L. Normal is typically under 5–10 mg/L, though labs vary.
Key caveat: Interestingly, CRP can be normal in active lupus even when ESR is elevated, this "dissociation" is actually a characteristic finding in SLE. High CRP in a lupus patient more often suggests infection than lupus flare.
Specific Autoimmune Antibodies
RF (Rheumatoid Factor)
What it measures: An antibody against the Fc portion of IgG, associated with rheumatoid arthritis.
Positive in: About 70–80% of RA patients. But also positive in Sjögren's, other autoimmune diseases, chronic infections, and up to 5% of healthy people.
Key caveat: RF is neither sensitive nor specific enough to diagnose RA on its own. About 20–30% of RA patients are RF-negative (seronegative RA).
Anti-CCP (Anti-Cyclic Citrullinated Peptide)
What it measures: Antibodies against citrullinated proteins, more specific for RA than RF.
Positive in: About 70–75% of RA patients; sensitivity similar to RF but specificity is higher (~95%).
Key advantage: Can be positive years before RA symptoms develop. High anti-CCP in early inflammatory arthritis strongly predicts progression to RA.
Anti-dsDNA (Anti-double-stranded DNA)
What it measures: Antibodies against double-stranded DNA, highly specific for lupus.
Positive in: About 70% of lupus patients. Very rarely positive in other conditions.
Special significance: Anti-dsDNA levels often correlate with lupus disease activity, rising during flares and falling during remission. Serial monitoring is valuable.
Anti-Smith (Anti-Sm)
What it measures: Antibodies against small nuclear ribonucleoproteins.
Positive in: About 25–30% of lupus patients, low sensitivity but very high specificity for SLE. A positive anti-Sm is highly predictive of lupus.
Anti-SSA (Ro) and Anti-SSB (La)
What they measure: Antibodies against RNA-binding proteins.
Positive in: Sjögren's syndrome (anti-SSA in ~75%, anti-SSB in ~50%), lupus, and neonatal lupus.
Clinical importance: Anti-SSA antibodies can cross the placenta during pregnancy and cause neonatal lupus, pregnant women with anti-SSA require specialist monitoring.
Anti-Scl-70 (Anti-Topoisomerase I)
What it measures: Antibodies against DNA topoisomerase I.
Positive in: About 30–40% of patients with diffuse cutaneous systemic sclerosis (scleroderma). Associated with higher risk of interstitial lung disease.
Anti-Jo-1
What it measures: Antibodies against histidyl-tRNA synthetase.
Positive in: About 20–30% of patients with inflammatory myositis (polymyositis/dermatomyositis). Associated with the "antisynthetase syndrome", myositis, interstitial lung disease, arthritis, and mechanic's hands.
Anti-U1-RNP
What it measures: Antibodies against U1-ribonucleoprotein.
Positive in: Mixed connective tissue disease (MCTD), characteristically in very high titres. Also seen in lupus and systemic sclerosis.
Other Important Tests
Complement (C3, C4)
Complement proteins are part of the immune system. In lupus, complement is consumed during active disease, low C3 and C4 in the context of other lupus features indicates active disease and is one of the monitoring tools rheumatologists use.
Full Blood Count (FBC/CBC)
Autoimmune disease commonly affects blood cells. Doctors look for: low white cell count (leucopenia), low platelet count (thrombocytopenia), and anaemia, all of which are features of lupus and other conditions, and all of which are part of diagnostic criteria.
Urinalysis (Urine Dipstick and Microscopy)
Kidney involvement is a serious complication of several autoimmune conditions, particularly lupus. Protein and blood in the urine (detected on dipstick) can indicate lupus nephritis even in the absence of symptoms. Regular urinalysis is part of lupus monitoring.
Blood tests are evidence, not verdicts. A positive antibody in the absence of symptoms rarely requires treatment. A negative blood test in the presence of clear clinical features doesn't exclude a diagnosis. Your doctor's job is to weigh all of this together.
Should I Have These Tests?
Our pre-test probability tool estimates which tests are most appropriate given your symptom pattern, and explains what each result would mean for you.