Evaluation of the BRAHMS Kryptor® Thyroglobulin Minirecovery Test in patients with differentiated thyroid carcinoma

Background: The present study was undertaken to evaluate a new sensitive thyroglobulin (Tg) mini-recovery test (Tg-mrec) for the detection of potential interferences in sera from patients with differentiated thyroid carcinoma (DTC) and low Tg levels. Methods: 167 DTC patients with serum Tg <2 mu g/L were enrolled. Both TgAb and Tg-mrec measurements were performed on the automated Kryptor (R) platform. Serum pretreatment in proprietory blocking tubes was perfomed to screen for heterophile antibody interferences. The concordance rates between tests were evaluated. Results: One case of over-recovery occurred in a patient with discordant Tg results in different immunoassays. The prevalences of a positive TgAb test and a reduced recovery rate were 15%-12%, respectively. Serum TgAb and Tg-mrec tests were both positive in 16 patients, both negative in 138 patients and discordant in 13 patients, respectively. The concordance rate between the Tg-mrec test and the TgAb assay was 92% (Cohens' kappa 0.894; 95% confidence interval: 0.82-0.93, p<0.001). In all, among seven clinically relevant interferences, three were found by TgAb, five by Tg-mrec and six by using both tests. Conclusions: The automated Kryptor (R) Tg-mrec test has a complimentary value to TgAb immunoassay testing in the detection of potential interferences in Tg measurements in patients with DTC and low Tg values (i.e., <2 mu g/L). Tg-mrec may detect interferences from TgAb not measured directly by an individual TgAb assay or from other interfering substances, such as heterophile antibodies.