RHEUMATOID FACTOR

Clinical use

Evaluate suspected autoimmune rheumatic diseases
Clinical background

Autoimmune rheumatic diseases are conditions in which the immune system attacks the joints and certain systems. They are often difficult to diagnose, as their symptoms can be vague, vary from patient to patient, and often overlap. Laboratory testing can provide useful information, but no single test provides a definitive diagnosis for any one rheumatic disease.

Diagnosis is most often based on a compilation of symptoms and signs, including clinical information and laboratory test results. Testing for antinuclear antibodies (ANAs) using an immunofluorescence assay (IFA) is a good first approach for laboratory evaluation of patients suspected of having certain autoimmune rheumatic diseases.

ANAs, a group of autoantibodies directed against diverse nuclear and cytoplasmic antigens, are associated with several autoimmune rheumatic diseases (Table 1). These include systemic lupus erythematosus (SLE), Sjögren syndrome, systemic sclerosis (SSc), and mixed connective tissue disease (MCTD). Although various platforms can be used to detect ANAs, an IFA with HEp-2 cells remains the gold standard because of its high sensitivity for several of the autoimmune rheumatic diseases.1,2 The high sensitivity stems from the large number of autoantigens (up to 150) in HEp-2 cells.

The diagnostic value of ANA testing varies with the specific clinical condition (Table 1). For example, positive ANA results are required for diagnosis of drug-induced lupus and MCTD.3 When SLE or SSc is suspected, ANA testing is recommended.3,4 While ANA testing is less useful (ie, not specific) for diagnosing polymyositis/ dermatomyositis, rheumatoid arthritis, and Sjögren syndrome, it can be used to screen for, or in the workup of, such diseases. When Sjögren syndrome is suspected, for example, testing can help clarify whether an underlying connective tissue disease exists.3,4