Clinical test reference range 7.86-14.4 μmol/L
Influencing factors 1. It is not affected by diet and exercise, has no daily rhythm, and can collect blood at any time. 2. It is not affected by iodine, mercury, and contrast agents, but is affected by serum binding globulin, and TT4 can be increased non-pathologically. 3. Serum should avoid repeated thawing.
clinical significance
FT 3 and FT 4 measurements are not affected by serum binding protein (TBG) content and are sensitive indicators reflecting thyroid function.
2. Elevated Found in:
① The acute phase of diffuse or nodular hyperthyroidism, autonomous high-functioning adenoma, subacute thyroiditis or painless thyroiditis;
② Excessive use of thyroxine (T4): ectopic TSH secretion in pituitary TSH tumors, chorioepithelial carcinoma, ovarian tumors, etc.;
③ Ectopic TSH secretion in pituitary TSH tumors, chorioepithelial carcinoma, ovarian tumors, etc.;
④Thyroid hormone unresponsiveness (pituitary type or central type). In pituitary type, the negative feedback inhibition disorder of pituitary gland on thyroid hormone is significantly increased.
3. Reduction is seen in:
① Primary hypothyroidism: congenital thyroid hypoplasia, thyroid hormone synthase disorder, idiopathic myxedema, chronic lymphocytic thyroiditis, iatrogenic hypothyroidism;
②Secondary (adenopituitary) hypothyroidism, tertiary (hypothalamic) hypothyroidism.
4. Comprehensive evaluation of multiple thyroid function indicators, the diagnostic value of hyperthyroidism is in the order of F T3 > F T4 > T3 > T4, and the diagnostic value of hypothyroidism is in the order of F T4 = TSH > T4 > F T3 > T3.