The anti-dsDNA (double-stranded DNA) ELISA is a blood test used to detect antibodies that mistakenly target the body's own DNA. Elevated levels of these antibodies are strongly associated with systemic lupus erythematosus (SLE), an autoimmune disease. The test involves coating a plate with dsDNA, adding the patient's blood sample, and detecting any bound antibodies using an enzyme-linked reaction. A positive result can aid in the diagnosis of SLE and help monitor disease activity.

THE RHEUMATOID FACTOR (RF) TEST DETECTS THE PRESENCE OF AN AUTOANTIBODY (AN ANTIBODY THAT ATTACKS THE BODYS OWN TISSUES) IN THE BLOOD. RF IS AN ANTIBODY AGAINST THE FC REGION OF IGG, ANOTHER TYPE OF ANTIBODY.

SM/RNP ANTIBODY IS DETECTED IN PATIENTS WITH MIXED CONNECTIVE TISSUE DISEASE. ANTIBODIES TO SM ARE HIGHLY SPECIFIC FOR SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) AND WHEN PRESENT ARE CONSIDERED A MARKER ANTIBODY. HOWEVER, THESE ANTIBODIES ARE FOUND IN ONLY 20% OF PATIENTS WITH SLE. RNP ANTIBODIES ARE FOUND IN 45% OF SLE PATIENTS BUT ARE ALSO OBSERVED IN NUMEROUS OTHER DISEASE STATES SUCH AS SJ GRENS SYNDROME, SCLERODERMA AND POLYMYOSITIS. IN SLE, RNP ANTIBODIES HAVE BEEN ASSOCIATED WITH A RELATIVELY BENIGN DISEASE COURSE WITH LOWER INCIDENCE OF RENAL AND CENTRAL NERVOUS SYSTEM INVOLVEMENT.

C4 IS CRITICAL TO ACTIVATION OF CLASSICAL PATHWAY. DECREASED LEVELS ARE SEEN IN PATIENTS WITH SLE, IMMUNE COMPLEX DISEASE AND HEREDITARY ANGIOEDEMA. CONGENITAL DEFICIENCY OF C4 INCREASES THE RISK OF RECURRENT BACTEREMIA ESPECIALLY S.PNEUMONIAE. THIS ASSAY IS USEFUL IN THE DIAGNOSIS OF C4 DEFICIENCY AND FOR INVESTIGATION OF A PATIENT WITH AN UNDETECTABLE TOTAL COMPLEMENT (CH50) LEVEL.

C3 IS AN ACUTE PHASE REACTANT. DECREASED LEVELS ARE SEEN IN PATIENTS WITH SLE, ENDOCARDITIS AND DIC. CONGENITAL DEFICIENCY OF C3 INCREASES THE RISK OF RECURRENT BACTEREMIA. THIS ASSAY IS USEFUL FOR THE DIAGNOSIS OF C3 DEFICIENCY AND FOR INVESTIGATION OF A PATIENT WITH AN UNDETECTABLE TOTAL COMPLEMENT (CH50) LEVEL.