Evaluation of a new in-vitro blood test for determining thyroid status: the effective thyroxine ratio.

Estimation of serum thyroxine concentration in test serum was performed in the presence of test serum itself and expressed as a fraction (Effective Thyroxine Ratio, E.T.R.) of serum thyroxine concentration similarly determined in normal serum. From studies of serum obtained from euthyroid, hyperthyroid, and hypothyroid patients and from euthyroid pregnant women and women taking contraceptive (oestrogen) medication, the E.T.R. estimation has been shown to have a diagnostic accuracy (99%) in defining thyroid status comparable to that shown by the free thyroxine index (98%). Because of the ease and rapidity with which the procedure can be completed, estimation of E.T.R. shows promise as a single, accurate measure of thyroid status.