Evaluation Of Thyroglobulin Autoantibodies Interference With Assay Of Thyroglobulin

Background and objective:Serum thyroglobulin(Tg) measurement is primarily used as a tumor marker to detect recurrent or persistent disease in patients with differenti- ated thyroid carcinomas.Unfortunately, serum Tg measurement is technically challeng -ing and there are sevrial problems that impair the clinical utility of the test.These limitations include between-method biases,suboptimal sensitivity; suboptimal inter- assay precision, "hook effect" problems (IMA methods) and Tg autoantibody (TgAb) interference. TgAb interference remains the most serious problem limiting the clinical value of serum Tg measurement. The direction and magnitude of the interference relates to the method and the concentration and affinity of the TgAb in the specimen. Radio- immunoassay(RIA), immunoradiometricassay (IRMA), chemiluminescent immuneoassay(CLIA), electrochemiluminescent assay(ECLIA) are used often in practice now. In order to find out the correlations and differences , we compared two kinds of method- RIA and ECLIA to measure Tg,TgAb and recovery tests.Methods:84 sera from 22 Graves'hyperthyroidism(GD),24 Hashimoto thyroiditis(HT)and 38 differentiated thyroid carcinomas(DTC),weremeasured Tg and TgAb by RIA and ECLIA. Recovery tests were carried out in 3 groups. 16 sera in first group were added 3 different Tg clibrator (50,100,200ng/mL Respectively. 12 sera with TgAb ^ 4000IU/ml in second group were diluted 5 times , Tg and TgAb were measured in each dilution, then added lOOng/mL Tg clibrator, respectively.56 sera in third group were divided into different subgroups by TgAb concentration with adding lOOng/mL Tg clibrator. Recovery(%) was calculated and concluded average values. Results:1> Tg values were both >10ng/mL in 31 sera by RIA and ECLIA, The correlation (r)between 2 assays is 0.676.Another 53 sera had Tg values< lOng/mL by ECLIA in which TgAb positive rate were 84%,87%by 2 methods,respectively. In 38 DTC sera, Metastatic subgroup had significantly higher Tg values than remain and athyroid subgroups by ECLIA(P=0.02,P=0.02), But 3 subgroup had little difference by RIA. 2> The correlation between 2 assays is 0.677 in TgAb measurement.Tg value decreased when TgAb concentration increased by ECLIA,while Tg value increased by RIA .TgAb value became lower when sera were duliated,Tg value also reduced by RIA while increased by ECLIA. 3^ The added Tg calibrator had not significant influence on Tg value and Recovery. Recovery was lower when TgAb concentration increased by ECLIA ,while increased by RIA. When sera were duliated, the recovery was increased by ECLIA while decreased by RIA. Conclusion: K RIA and ECLIA has good correlation with Tg measurement in 10~400ng/mL. ECLIA had wider range and better sensitivity than RIA. 2^ Although RIA and ECLIA has different principle and unit with TgAb measurement, they has good correlation. Tg value were affected by TgAb in both assays.Tg value were underestimated by ECLIA .while overestimated by RIA. After sera were duliated, Tg value became increasing by ECLIA. More study is needed for the RIA values. 3 -. The added Tg calibrator had not significantly influence on Tg value and Recovery. When sera were duliated, the recovery was increased by ECLIA while decreased by RIA. TgAb concentration had significant influence on Recovery by ECLIA assay. Rrecovery test can not efficiently rectify Tg value when TgAb was positive.