Diagnosis of systemic inflammatory rheumatic disease: rational use of laboratory investigations

ABSTRACT

There is no substitute for good clinical diagnosis before ordering investigations for systemic inflammatory rheumatic diseases. Even the most sensitive and specific investigation may be rendered worthless if carried out in persons who are least likely to have that disease. The sequence of events should include clinical diagnosis followed by assessment of laboratory parameters of "acute phase reactions" to confirm the on-going systemic inflammation and finally the specialized investigations to narrow down the diagnosis, determine the severity and sometimes the prognosis of the disease process. Specialized investigations include; rheumatoid factor [RF] which is mainly used for determining prognosis of patients with rheumatoid arthritis; Anti-nuclear antibody [ANA] an excellent screening test for suspected systemic lupus erythematosus [SLE], Anti-dsDN A antibody test useful for SLE activity and predicting relapse; Anti-neutrophil cytoplasmic antibody [ANCA] for systemic vasculitis, Anticardiolipin antibodies [aCL] in patients suspected of antiphospholipid syndrome, Complement C3 and C4 determinations for suspected immune-complex mediated renal diseases. It is to be noted that except for a few of these specialized investigations, the majority are not influenced in short term by the disease process or treatment