Analytical and clinical evaluation of a new one-step non-analogue radioimmunoassay for serum-free thyroxine

Abstract

We evaluated analytically and clinically the new one-step non-analogue free thyroxine (FT4) assay (Amerlex-MAB from Amersham), using a labelled monoclonal thyroxine-specific antibody as tracer, in comparison with the Gammacoat two-step FT4 kit (Baxter). Analytical performances of the new kit were excellent: within and between run coefficients of variation were less than 5% in the working range. Clinical sensitivities for hypo- and hyperthyroidism were comparable for both kits (FT4 Amerlex-MAB 95% confidence interval: 12-25 pM). When serum was supplemented with albumin we observed a slight decrease in FT4 values measured by both kits. When oleate was added to serum we noted a moderate increase with the Amerlex-MAB kit up to 10 mM oleate added and a much more marked increase with the two-step kit. Results obtained with patients from particular euthyroid populations, known to have low albumin or high free fatty acids concentrations or to have perturbed FT4 results when measured by an analogue-based method, agreed with those of the in vitro studies. With these patients the specificity of the Amerlex-MAB FT4 results was good but slightly decreased compared with the two-step FT4 method, except for heparin-treated patients who were all classified according to their euthyroidal status (17/17 instead of 13/17 with the two-step kit).

Bio-Available Testosterone Levels Fall Acutely Following Myocardial Infarction in Men: Association With Fibrinolytic Factors

“…[3] Plasma levels of both total and bio-available testosterone (but not 17b-estradiol or DHEAS) fell transiently in the first 24 hours after myocardial infarction. Several previous studies have reported a transient reduction in total testosterone following infarction, [10][11][12][13][14] although the published data are not consistent. [15] In this study, we measured the bio-available fraction of testosterone as well as total testosterone, giving a more accurate picture of changes in plasma testosterone levels.…”

“…Several studies have demonstrated that testosterone levels fall transiently following acute myocardial infarction, [10][11][12][13][14] although Markova et al found a rise in testosterone levels early after myocardial infarction. [15] However, in these studies, plasma total testosterone was measured, which may not accurately reflect the active fraction of circulating testosterone available to the tissues (bio-available testosterone).…”

Avoiding Misdiagnosis Due to Antibody Interference with Serum Free Thyroxin

“…In immunometrics one-step assays, physicochemical differences arising from the binding of labeled antibodies to the solid, support confer kinetic differences that result in decreased analogue affinity for endogenous binding proteins and thus produce more reliable free hormones results ( 20 , 21 ). The antiT4-autoantibodies present in the patient’s sample represent another endogenous binding protein.…”