Measurement of thyroxine conversion to triiodothyronine using human lymphocytes. A useful and simple laboratory technique.

The deiodination of T4 to T3 has been studied after incubation of whole lymphocytes with different T4 concentrations, followed by a T3 radioimmunological determination performed on unextracted samples. The lymphocytes were isolated from blood from normal volunteers of both sexes and different age classes as well as from myxedematous subjects and patients with low T3 syndrome. The T3 production, in normal subjects, expressed as pmol/10.10(6) cells was 0.41 +/- 0.75 (T4 = 4.10(-7) M, n = 12), 1.43 +/- 0.14 (T4 = 4.10(-6) M, n = 26) and 1.65 +/- 0.29 (T4 = 8.10(-6) M, n = 11). There was no sex or age-related difference. In 3 myxedematous patients the T3 production was lower than the corresponding value obtained in normal subjects. The T3 production in patients with low T3 syndrome was lower than in controls (p less than 0.001); an inverse correlation was found between the T3 production and the serum rT3 levels, whereas no correlation could be found with serum T3 levels.