Falsely elevated thyroid hormone levels due to anti-sheep antibody interference in an automated electrochemiluminescent immunoassay.
We describe a 43-year-old woman with falsely increased thyroxine (T(4)) and triiodothyronine (T(3)) concentrations (total and index values) using a competitive electrochemiluminescent immunoassay, due to human anti-sheep antibodies. The thyrotropin (TSH) concentration was within normal limits. When specimens were re-tested by an immunoassay utilizing mouse antibodies, the total T(4) and T(3) concentrations were within normal limits. Removal of IgG by protein G column chromatography resulted in normalization of total T(4) and T(3) concentrations. In contrast, a mouse IgG column failed to normalize the elevated total T(4) and T(3) concentrations. Other immunoassays utilizing mouse monoclonal antibodies and rabbit antisera were unaffected, indicating that the interference was anti-sheep antibodies and not heterophile antibodies. We believe this is the first report of human anti-sheep antibodies causing falsely increased total and free T(4) and T(3) serum concentrations in competitive immunoassays using sheep antisera. Clinicians need to be aware of this potential problem since inaccurate thyroid function tests can lead to inappropriate treatment decisions.
Monchamp
Travis
T
Department of Medicine, Division of Endocrinology, Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1732, USA.
Chopra
Inder J
IJ
Wah
David T
DT
Butch
Anthony W
AW
D000328:Adult; D000818:Animals; D000910:Antibodies, Heterophile / Q000096:biosynthesis*; D004563:Electrochemistry / Q000379:methods; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D049449:Luminescence; D012756:Sheep; D013963:Thyroid Hormones / Q000096:biosynthesis*; D013974:Thyroxine / Q000096:biosynthesis; D014284:Triiodothyronine / Q000096:biosynthesis
D000910:Antibodies, Heterophile; D013963:Thyroid Hormones; D014284:Triiodothyronine; D013974:Thyroxine