Summary The StaT4 test is a technically simple test of thyroxine measurement, which apparently gives results in good agreement with those derived by radioimmunoassay in most patients. In pregnancy, however, falsely low serum thyroxine values were found with the StaT4 test when compared with either a radioimmunoassay or the Thyopac-4 test. Detailed studies showed that the discrepancy resulted from the extraction technique used in the StaT4 test, which appears to allow the patient's thyroxine binding proteins to remain in the assay system. Similar method discrepancies were observed in other clinical conditions associated with elevated thyroxine binding globulin concentration. This study, as well as being of practical clinical importance, has implications for the design of competitive protein binding tests of thyroid function.
References
1.
BairdS. G.ThomsonJ. E.BeastallG. H.LogueF.WatsonR.ThomsonJ. A. (1977). Discrepancies in thyroxine measurement in pregnancy between radioimmunoassay and competitive protein binding (Oxford StaT4). Annual Meeting of the Thyroid Club, London, 1977.
2.
BurrW. A.EvansS. E.HoganT. C. (1977). T4 radioimmunoassay and thyroxine binding globulin concentration. Lancet, 1, 757.
3.
ChallandG. S.RatcliffeW. A.RatcliffeJ. G. (1975). Semi-automated radioimmunoassays for total serum thyroxine and triiodothyronine. Clinica Chimica Acta, 60, 25–32.
4.
DowlingJ. T.FreinkelN.IngbarS. E. (1956). Thyroxine-binding by sera of pregnant women. Journal of Clinical Endocrinology and Metabolism, 16, 280.
5.
GershengM. B.LarsenP. R.RobbinsJ. (1976). Radioimmunoassay for serum thyroxine-binding globulin: Results in normal subjects and in patients with hepatocellular carcinoma. Journal of Clinical Endocrinology and Metabolism, 42, 907–911.
6.
HollanderC. S.ScottR. L.TschudyD. P.PerlrothM.WaxmanA.SterlingK. (1967). Increased protein bound iodine and thyroxine binding globulin in acute intermittent porphyria. New England Journal of Medicine, 277, 995–1000.
7.
LiewendahlK.HeleniusT. (1976). Effect of fatty acids on thyroid function tests in vitro and in vivo. Clinica Chimica Acta, 72, 301–313.
8.
RobbinsJ. (1975). Thyroxine-binding proteins. In Progress in Clinical and Biological Research. Vol. 5: Trace Components of Plasma: Isolation and Clinical Significance, edited by JamiesonG. A.GreenwaltT. J., pp. 331–355. Liss, New York.
9.
RobbinsJ.NelsonJ. H. (1958). Thyroxine-binding by serum protein in pregnancy and in the newbornJournal of Clinical Investigation, 37, 153–159.
