Thyroid Function Measured by In Vitro Erythrocyte Uptake (Red-Cell Uptake) of I131-Labeled l-Triiodothyronine*
O. PETER SCHUMACHER, M.D., Ph.D.
Department of Endocrinology and Metabolism
JOHN W. KING, M.D., Ph.D.
Department of Clinical Pathology
SINCE it is now known1–3 that there are differences in the amount of thyroxin-binding protein in the blood, in the various grades of thyroid activity, the work of Hamolsky and associates,4,5 and Crispell, Kahana, and Hyer6 suggested that one might estimate the amount of thyroxin-binding protein, and study thyroid function clinically, by the in vitro erythrocyte uptake of I131-labeled l-3, 5, 3 prime-triiodothyronine (TRI131 red-cell uptake, hereinafter called RCU). Others have shown that there are many factors that altered the RCU of l-triiodothyronine other than the grade of thyroid function. It is decreased in pregnancy,4–8 during estrogen therapy, and increased with Dicumarol† therapy, nephrosis, hepatic disease, emphysema, and severe illness9 of any cause. Since the evidence to date indicates that this parameter of thyroid function is rarely affected by exogenous iodine medication, there are many4–8 who believe it probably will have considerable clinical usefulness. This report is a summary of our experience with 133 determinations in patients who had various thyroid disorders.
As previously described by Hamolsky and associates,4,5 and by Crispell, Kahana, and Hyer6 the method consists principally of adding a standard solution of TRI131 to 5 ml. of oxalated, citrated, or heparinized blood. In our initial experiment, oxalated blood was used, but now EDTA‡ is used as an anticoagulant. The blood was collected in a commercially prepared vacuum collection tube, and it was found that some coagulation took place when the TRI131 was added to the oxalated blood unless the amount of oxalate in the tube . . .