The diagnosis of systemic lupus erythematosus: How the laboratory can help you

Systemic lupus erythematosus is a heterogeneous disease with diverse clinical features. Laboratory tests are useful in supporting the diagnosis as well as in assessing disease activity. Although antinuclear antibodies are not specific, a titre of >1/160 by immunofluorescent test in a patient with multisystem disease is highly suggestive of underlying SLE. Anti-dsDNA and anti-Sm antibodies are highly specific for idiopathic SLE. In addition, antiphospholipid antibody assays, serum complement C3 and C4 together with ESR and CRP measurements are helpful in corroborating the diagnosis. A combination of anti-dsDNA, serum complement C3 and C4, ESR and CRP, supported by relevant tissue histology, probably provides the most useful information on disease activity, in particular patients with lupus nephritis. However, results of any laboratory test should always be interpreted with reference to the clinical presentation.