We performed a limited evaluation of four free thyroxin (FT4) reagent kits: the Amerlex-M (AFT4), the Amerlite (LFT4), the MagicLite (MFT4), and the GammaCoat two-step RIA (GFT4). FT4 was measured in specimens from 201 subjects: 19 healthy controls, 14 patients who were thyrotoxic, 13 who were hypothyroid, 59 who had a past history of thyroid disease, seven with thyroxin autoantibodies, seven who were taking amiodarone, and 82 who had no clinical indication of thyroid hormone abnormality. Of these 201 subjects, 78 had a low serum albumin (less than 35 g/L) and 27 had severe nonthyroidal illness. We also investigated 60 pregnant subjects. We found no correlation between thyroxin-binding globulin (TBG) and FT4 in any of the assays, and only the AFT4 method showed a significant correlation with albumin concentrations. The presence of autoantibodies to thyroxin affected the results of all methods except the GFT4 method. All methods showed a decrease in mean FT4 values in late pregnancy. Correlation of patients' clinical state and FT4 results suggested that the reference ranges published by the manufacturers need to be modified for our laboratory.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.