Clinical Chemistry, Vol 40, 1940-1943, Copyright © 1994 by American Association for Clinical Chemistry

Endogenous serum antibodies that interfere with a common thyroid hormone uptake assay: characterization and prevalence

D Ritter, W Brown, MH Nahm, JH Ladenson and MG Scott
Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110.

We identified individuals whose serum contained a substance that produced falsely decreased thyroid hormone (T)-uptake values determined by the Emit (Syva) procedure. Investigation of this interference was prompted by identification of a patient with T-uptake values inconsistent with clinical assessment. IgG depletion and supplementation studies with this patient's serum suggested that the interference was due to endogenous antibodies with specificity for the thyroxine-glucose-6-phosphate dehydrogenase conjugate in the Emit T- uptake assay. The prevalence of the interference was examined by prospectively comparing routine Emit T-uptake values of 1710 patients' samples to T-uptake values obtained by another method. Discrepant samples were also assayed by a radioactive binding triiodothyronine- uptake assay. We identified eight samples that had falsely decreased T- uptake values by Emit, for an overall prevalence of 0.46%. Among 45 consecutive patients with a T-uptake value < 20%, five patients, or 11%, were falsely decreased by Emit and three of these were clearly due to an interfering IgG. We suggest that samples with abnormally low T- uptake values determined by the Emit method be confirmed by an alternative method.

The following articles in journals at HighWire Press have cited this article:

				N. Despres and A. M. Grant Antibody interference in thyroid assays: a potential for clinical misinformation Clin. Chem., March 1, 1998; 44(3): 440 - 454. [Abstract] [Full Text] [PDF]