Endogenous serum antibodies that interfere with a common thyroid hormone uptake assay: characterization and prevalence.
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.
Ritter
D
D
Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110.
Brown
W
W
Nahm
M H
MH
Ladenson
J H
JH
Scott
M G
MG
D000328:Adult; D000918:Antibody Specificity; D001323:Autoantibodies / Q000097:blood*; D017248:Enzyme Multiplied Immunoassay Technique / Q000706:statistics & numerical data*; D005188:False Negative Reactions; D005260:Female; D005954:Glucosephosphate Dehydrogenase / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood / Q000276:immunology; D014284:Triiodothyronine / Q000097:blood
D001323:Autoantibodies; D007074:Immunoglobulin G; D013963:Thyroid Hormones; D014284:Triiodothyronine; D013972:Thyrotropin; D005954:Glucosephosphate Dehydrogenase; D013974:Thyroxine