Abstract:

Objective To evaluate the performance of reverse triiodothyronine（rT₃） determination by chemiluminescence assay. Methods The precision,accuracy,analytical sensitivity,analytical specificity,linearity,reference range and methodological comparison of rT₃ determination by chemiluminescence assay were evaluated according to EP documents of the Clinical and Laboratory Standards Institute（CLSI）. The levels of 3,5,3'-triiodothyronine（T₃）,thyroxine（T₄）,thyroid-stimulating hormone（TSH） and rT₃ were determined in 50 healthy subjects（healthy control group） and 131 patients,including 30 preliminarily diagnosed hyperthyroidism patients（hyperthyroidism group）,28 hyperthyroidism patients with treatment for 1 month（hyperthyroidism treatment group）,25 preliminarily diagnosed hypothyroidism patients（hypothyroidism group）,23 hypothyroidism patients with treatment for 1 month（hypothyroidism treatment group） and 25 primary non-thyroid diseases [euthyroid sick syndrome （ESS）]. Results For high-level and low-level quality control materials of rT₃,the within-run coefficients of variation（CV）were 4.82% and 4.95%,and the between-run CV were 7.51% and 5.90%,respectively. The biases were -1% and 1%. The linearity was 0.05-10.07 ng/mL,and the reference range was 0.20-0.95 ng/mL. There was a good correlation between chemiluminescence assay with radioimmunoassay（r=0.952）. Compared with healthy control group,the levels of rT₃,T₃ and T₄ in hyperthyroidism group were increased（P<0.05）,and TSH was decreased（P<0.05）. In hypothyroidism group,the levels of rT₃ and T₄ were decreased（P<0.05）,and TSH was increased（P<0.05）. Compared with hyperthyroidism group,hyperthyroidism treatment group had decreased rT₃,T₃ and T₄ levels（P<0.05）,and TSH was increased（P<0.05）. Compared with hypothyroidism group,hypothyroidism treatment group had increased rT₃ and T₄ levels（P<0.05）,and TSH decreased（P<0.05）. The level of rT₃ in ESS group was higher than those in hypothyroidism and healthy control groups（P<0.05）,the levels of T₃ and T₄ were lower than those in healthy control group（P<0.05）,there was no statistical significance compared with hypothyroidism group（P>0.05）,TSH level was lower than that in hypothyroidism group（P<0.05）,and there was no statistical significance compared with healthy control group（P>0.05）. Conclusions The determination of rT₃ by chemiluminescence assay has good precision,accuracy,specificity and linearity,which is suitable for large scale sample determination. It can be used for the differential diagnosis of hypothyroidism and ESS.

Key words: Reverse triiodothyronine, Chemiluminescence assay, Methodological evaluation