[Judicious use of biological tests in rheumatology]

Among the numerous biologic and immunologic complementary tests the clinician has at his disposal some that document inflammation (ESR, c-reactive protein, complement components, electrophoretic and immunoelectrophoretic profiles) are not specific while others that permit etiologic classification (rheumatoid factor, antinuclear antibodies, genetics of the histocompatibility system, serologic test for microorganisms) are specific but not necessarily related to activity or disease process. None of these tests has absolute diagnostic power. It is therefore important to know their relative clinical significance in order to avoid unnecessary and costly investigations whose interpretation may pose more problems than solve questions.