Diagnosis of rheumatoid arthritis. Medical and laboratory aspects.

The diagnosis of rheumatoid arthritis (RA) is largely dependent on the existence of a characteristic pattern of clinical symptoms and signs that must be present for at least six weeks. Early morning joint stiffness and symmetric polyarticular inflammation, particularly in the metacarpophalangeal, proximal interphalangeal, wrist, and metatarsophalangeal joints, are typical of the disease. Extraarticular disease, including rheumatoid nodules, is usually associated with severe and well-established arthritis, and occular, pulmonary, cardiac, neurologic, and vasculitic involvement can be a considerable source of morbidity. Serologic testing for rheumatoid factor (RF) is helpful in confirming the diagnosis since 80% of patients are seropositive, but RFs are expressed in many other disease states. Expression of multiple RF isotypes differentiates RA from other populations. Erythrocyte sedimentation rates, C-reactive protein levels, circulating immune complexes, and platelet counts are often elevated in RA and serve as indicators of disease activity.