Rheumatology/ connective tissue disease

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The tests described in this section are very non-specific. Some (ANA, rheumatoid factor) are found in completely healthy people, particularly older women. These can also be transiently positive in infection or as the result of drugs (particularly anti DNA). This means that these tests should not be used as a ‘screen’ for investigating patients with raised ESRs or general malaise.

Rheumatoid factor is especially prone to misinterpretation. It is resent in 15% of normal individuals and is not diagnostic of rheumatoid arthritis. Rheumatoid arthritis is diagnosed by finding symmetrical peripheral polyarthritis with erosions on X-ray.

The half-life of IgG antibodies is about three weeks, so most forms of treatment will not produce rapid changes in autoantibody levels and repeat sampling more than every six weeks is probably unhelpful. We would advocate that it is nearly never useful to repeat positive ENA antibodies.

Patient information

Patient information is available from:

Screening for Systemic Autoimmune Disease

Relevant immunological tests:

Systemic Lupus Erythematosus

Relevant immunological tests:

Criteria for the diagnosis of SLE include antinuclear antibodies (ANA), antibodies to ds DNA, (Crithidia assay if appropriate) antibodies to extractable nuclear antigens (ENA) and anti cardiolipin antibodies.

The presence of particular groups of serum antibodies may be associated with different clinical patterns of disease activity.

Other typical immunological findings include raised serum IgG, and low serum complement levels (C3, C4) as well as the presence of rheumatoid factor, and other autoantibodies.

DNA antibody levels, C4 levels (and ESR) are of some help in monitoring disease activity.

Sjögren’s syndrome

Relevant immunological tests:

There may be considerable overlap with other autoimmune disorders, including SLE.

Characteristically antinuclear antibodies and antibodies to extractable nuclear antigens (particularly antibodies to Ro or SS-A, and antibodies to La or SS-B) are found.

Rheumatoid factor and raised immunoglobulins may be found.

Scleroderma/systemic sclerosis

Relevant immunological tests:

The Scl-70 antibody is associated with systemic sclerosis, while centromere antibodies are found in limited systemic sclerosis (CREST syndrome).

Polymyositis/Dermatomyositis

Relevant immunological tests:

Jo-1 antibodies are found in a subset of myositis patients, especially those with interstitial lung disease.

Antiphospholipid antibody syndrome

Relevant immunological tests:

Recurrent arterial or venous thrombosis (or foetal loss) may be associated with antibodies to phospholipids including cardiolipin. Related antiphospholipid antibodies include the lupus anticoagulant.

Cardiolipin antibodies may be found in other autoimmune disorders, particularly SLE and are also seen very frequently in acute and chronic infections.

Guidelines suggest that two positive tests (anticardiolipin antibodies, “lupus anticoagulant” – haematology) more than six weeks apart are required to diagnose antiphospholipid syndrome.

More information is available from the BCSH (British Committee for Standards in Haematology) guidelines.

 

(Last reviewed September 2024)