J Korean Soc Endocrinol.
1994 Jun;10(2):98-104.
Evaluation of the Usefulness of Free T4 Measured by 2 - Step Iimmunoextraction in the Patients with Thyroid and Non - Thyroid Diseases
Abstract
- Many methods and commercial kits have become available for directly measuring free thyroxine(free T_4). However, most of them are inadequate for routine laboratory use because of their complexity and inaccuracy. Recently, 2-step RIA methods by immunoextraction(2-step immunoextraction) for free T_4 have been developed to improve its accuracy and convenience. We evaluated the usefulness of free T_4 measured by 2-step immunoextraction compared to free T_4 index(FT_4I), free T_4 measured by 1-step RIA, and TSH in 204 patients with thyroid and non-thyroid disease. There were no differences in sensitivities and specificities of free T_4(1-step, 2-step), FT_4I and TSH in the patients with hyperthyroidism and euthyroid nodule. However, the sensitivity of TSH in hypothyroidism was remarkablely higher than the others(100.0% vs. 61.5-81.5%). The sensitivity of free T_4(2-step) was also higher than those of free T_4(1-step), FT_4I and TSH in the patients with non-thyroid disease(94.3% vs. 74.3-83.8%). The values of free T_4 measured by 1-step RIA were significantly lower than those by 2-step immunoextraction, especially in the patients with non-thyroid disease(1.10+-0.04 vs. 1.55+-0.03ng/dL, p<0.05).In conclusion, no significant differences were found in sensitivity and specificity of free T_4(1-step, 2-step), FT_4I, and TSH in the patients with thyroid diseases except in hypothyroidism. However, the sensitivity of free T_4 measured by 2-step immunoextraction was significantly higher than the other tests, especially in the patients with non-thyroid disease. Therefore, free T_4 assay using 2-step immunoextraction is useful to differentiate the non-thyroid disease from thyroid diseases.
