The variability of immunologic laboratory tests.
To determine the clinical reliability of certain immunologic tests, serum complement (C3), DNA binding (DNAB), and fluorescent antinuclear antibody (FANA) were measured blindly at 2 university immunology laboratories on duplicate serum samples from 667 patients with connective tissue diseases. Twenty-seven percent of patients were differently classified as normal or abnormal for C3 by the 2 laboratories. The mean of paired differences was 25 mg% and large variability remained even after adjustment. Repeat assays on a random subset of 91 sera showed persistent variability. Fifteen percent of patients were differently classified by their DNAB results in 11% by FANA tests. Considering this variability, these "objective" laboratory tests alone are not sufficiently reliable for accurately defining diseases or disease activity.
D000906:Antibodies / Q000032:analysis*; D000974:Antibodies, Antinuclear / Q000032:analysis*; D003176:Complement C3 / Q000032:analysis*; D003240:Connective Tissue Diseases / Q000175:diagnosis; D004247:DNA / Q000276:immunology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D005779:Immunodiffusion; D007158:Immunologic Techniques / Q000592:standards*
D000906:Antibodies; D000974:Antibodies, Antinuclear; D003176:Complement C3; D004247:DNA