Triiodothyronine (T3) -autoantibodies in two goitrous patients
Wiersinga, W.M.; Buurke, E.J.; Schreuder, H.B.; Endert, E.; Touber, J.L.
Netherlands Journal of Medicine 25(5): 121-126
1982
ISSN/ISBN: 0300-2977 PMID: 7099315 Document Number: 189867
Two goitrous patients with triiodothyronine (T3) autoantibodies are described. Thyroid function tests were compatible with mild or subclinical hypothyroidism except for plasma T3 values, which were very high or undetectable, depending on the T3-RIA used. The cause of the odd T3 values was abnormal binding of T3 to Ig (subclass IgG) in the plasma samples from the 2 patients. These gamma-globulins acted as T3 antibodies of the high-affinity low-capacity type: Scatchard plots of the binding of T3 to IgG in the 2 patient samples disclosed an affinity constant of 1.64 and 3.07 .times. 1010 L/M, and a maximal binding capacity of 21.73 and 4.08 .times. 10-9 M/L, respectively. Plasma T3 concentrations as measured by RIA after ethanol extraction were 3.68 and 1.94 nmol/l, respectively. T3-autoantibodies interfere with the T3-RIA, leading to spuriously high or low values, depending on correction for non-specific binding and on the method used to separate bound and free hormone; prior ethanol extraction circumvents this technical error; T3-autoantibodies have minor or no biological significance.