Preparation of I-131-labeled human serum prealbumin and its metabolism in normal and sick patients.

Despite some early doubts concerning its presence in plasma and its physiological function (1-4), the thyroxine-binding prealbumin of human serum (TBPA) is now known to play a significant role in the transport of thyroxine (T4) (5-8). Normally, as assessed by in vitro techniques, TBPA appears to bind at least 25 to 35%o of T4 in serum (5, 6). In the serum of many patients with severe acute or chronic illness, however, the proportion of endogenous T4 in serum bound by TBPA and the T4-binding capacity of TBPA decline (8, 9). The recent availability of substantial quantities of a highly purified preparation of TBPA has made possible an investigation of the in vivo metabolism of this protein in normal patients and in patients with a variety of disorders that lead to decreased binding of T4 by TBPA in serum. In addition, the cause of this decrease in T4 binding in the serum of such "sick" patients has been evaluated. A portion of the findings has been presented in abstract form (10). While these studies were in progress, Oppenheimer, Surks, Bernstein, and Smith reported similar studies in abstract form (11, 12).