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Journal of Clinical Endocrinology & Metabolism Vol. 43, No. 1 26-31
doi:10.1210/jcem-43-1-26
Copyright © 1976 by the Endocrine Society.
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Effect of Halofenate on Serum Thyroid Hormone Determinations in Vitro

FRED E. KARCH, JOHN P. MORGAN, NORMAN P. KUBASIK and H. E. SINE

Departments of Pharmacology and Toxicology, and of Medicine University of Rochester of Medicine and Dentistry Rochester, NewYork 14642 Clinical Laboratories Genesee Hospital, Rochester, New York 14607

Send reprint requests to: Fred E. Karch, M.D., Department of Pharmacology and Toxicology, University of Rochester Medical Center, Rochester, New York 14642.

Halofenate has been shown to decrease thyroxine (T4) binding to thyroxine-binding globulin (TBG) in vitro. Several indirect serum thyroid hormone assays are dependent on thyroid hormone binding and the results might be altered by halofenate in the serum. Halofenate free acid (50-500 µg/ml) was added to serum samples in vitro, and the samples were assayed for total serum T4 by competitive protein-binding assay (CPB) and radioimmunoassay (RIA), the per cent of dialyzable T4 (%FT4), total serum triiodothyronine (T3) by RIA, and resin T3 uptake (RT3U). Halofenate increased xincreased the measured T4 (CPB), %FT4, T3 (RIA), and RT3U, but did not alter the T4 (RIA) determination. Thus, halofenate appears to diminish T4 binding to TBG in vitro, and artifactually alters the serum determinations of T4 (CPB), %FT4, T3 (RIA), and RT3U. Calculated values derived from these measurements for the free thyroxine index and "free" T4 will also be affected by halofenate. Only the T4 (RIA) determination was unchanged by the presence of halofenate in vitro.

Supported In Part By A Grant From Merck, Sharp, And Dohme Research Laboratories, West Point, Pennsylvania.

Received October 28, 1975.






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Copyright © 1976 by The Endocrine Society