The variability of immunologic laboratory tests
Feigenbaum, P.A.; Medsger, T.A.; Kraines, R.G.; Fries, J.F.
Journal of Rheumatology 9(3): 408-414
1982
ISSN/ISBN: 0315-162X PMID: 6811741 Document Number: 191962
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.