Diagnosis of systemic lupus erythematosus. The value of immunologic tests.

A variety of immunologic tests are now available to assist the clinician in the differential diagnosis of systemic lupus erythematosus (SLE) and related disorders. Knowledge of the sensitivity and specificity of each test is critical for proper clinical interpretation. Also important is a detailed consideration of the clinical situation and the pretest estimate of the likelihood SLE is present. The antinuclear antibody (ANA) test is the most sensitive test for SLE and is therefore the best screening assay for ruling out its presence. Anti-native (N)-DNA and anti-Sm (Smith antigen) tests are highly specific for SLE and have strong confirmatory powers, even in a patient unlikely to have the disease. New information regarding the operating characteristics of tests for SLE and a recent trend toward more analytic and cost-conscious use of the laboratory should allow clinicians to make more rational and cost-effective decisions about methods of diagnosis. Combination sequential testing seems to be a logical approach.