ELISA FOR THYROGLOBULIN IN SERUM - RECOVERY STUDIES TO EVALUATE AUTOANTIBODY INTERFERENCE AND RELIABILITY OF THYROGLOBULIN VALUES

An ELISA for measuring thyroglobulin (Tg) in serum was developed with polyclonal antibodies to Tg on the solid phase and two monoclonal anti bodies to Tg as the second antibodies. The assay has a detection limit of 1 mu g/L, a within-run imprecision (CV) of <7%, and a between-run CV of < 10%, Parallelism of the assay was shon n in dilution studies, in which the percent observed/expected values for n = 5 autoantibody-c ontaining samples gave a mean of 99 % (SD 13.1%); for n = 5 samples wi th undetectable autoantibody concentrations, the mean was 103% (SD 11. 8%), The correlation of the ELISA with an RIA for Tg in 46 normal samp les was ELISA = 1.11 (RIA) + 0.52, S-y\x = 2.23, SD intercept = 0.54, SD slope = 0.03, range = 0 to 53 mu/L, r = 0.980. Comparison of the EL ISA with a reference laboratory RI4 for 29 clinical samples gave a cor relation of: ELISA = 1.53 (RIA) - 0.48, S-y\x = 9 00, SD intercept = 2 .19, SD slope = 0.10, range = 0 to 98 mu g/L, r = 0.950. To provide ad ditional information concerning the reliability of the Tg measurement in samples containing autoantibodies to Tg, we developed a procedure f or determining the percent recovery. A percent recovery greater than o r equal to 80% indicates minimal interference by autoantibodies in thi s assay. The assay is straightforward to perform, results can be poste d within 8 h, and the routinely good recovery of Tg in the presence of Tg autoantibodies indicates minimal autoantibody interference in this assay.