The labeled triiodothyronine (determination of thyroid function with it). Labeled J 131 1, 3, 5, 3-triiodothyronine is added in vitro to blood taken from the test, and according to the degree of accumulation of triiodothyronine in erythrocytes, the activity of the thyroid gland is judged. For the concentration of labeled triiodothyronine in erythrocytes, they must be incubated in a water bath with periodic shaking at an optimum temperature of 37 °. According to the authors, pre-administration of stable iodine is almost not reflected in the test indicators, while treating thyrotoxicosis with antithyroid agents (iodides, methylthiouracil) or hypothyroidism with thyroid hormones, repeated studies of thyroid function give the correct idea of the course of the disease under treatment conditions.
Blood is taken on an empty stomach or after a meal in a test tube with an oxalate mixture, citrate or moistened with heparin. To 3 ml of blood, add 0.1 ml of a solution of labeled triiodothyronine at a concentration of 10-120 · 10-1 mg in 0.1 ml of saline. Test tubes with blood and a solution of labeled triiodothyronine are placed for 2 hours in a water bath at a temperature of 37 °, where they are periodically shaken. After incubation of the blood for 2 hours in a water bath, the radioactivity is determined by a well scintillation counter, then centrifuged.
The upper liquid layer is carefully removed, and a tenfold volume of saline is added to the remaining red blood cells, followed by repeated centrifugation followed by removal of the upper liquid layer. Such centrifugation is carried out five times. After the last centrifugation, erythrocyte radioactivity is determined. The percentage of accumulation of labeled triiodothyronine in red blood cells is determined by the formula
the percentage of accumulation in erythrocytes = erythrocyte radioactivity / blood radioactivity x 100 patient's hematocrit / hematocrit
Incubation time ranges from 30 minutes to 5 hours. The accumulation of triiodothyronine in erythrocytes with a long incubation period increases slightly.
A decrease in the accumulation of labeled triiodothyronine in erythrocytes was found during pregnancy and estrogen administration. An increase in accumulation is observed in nephrosis, severe liver damage (cirrhosis, metastasis of malignant tumors), severe pulmonary insufficiency with accumulation of carbon dioxide in the tissues, atrial paroxysmal arrhythmia, and with the introduction of anticoagulants. Sample rates remained normal in euthyroid goiter, hypertension, cardiac decompensation, and diabetes mellitus.