A Solid Phase, Sandwich-Type Radioimmunoassay forAntithyroglobulin: Elimination of False Positive Resultsand Semiquantitative Measurement of Antithyroglobulinin the Presence of Elevated Thyroglobulin*

Abstract

Thyroid disorders can be associated with elevatedconcentrations of serum antithyroglobulin antibodies(anti-Tg) and/or thyroglobulin (Tg), but none of the availableanti-Tg assays deals with anti-Tg measurements in the presenceof abnormally high Tg levels. The competitive binding radioassay produces falsely elevatedvalues for anti-Tg if serum Tg is elevated and either falselyelevated or depressed values if both Tg and anti-Tg are abnormallyhigh. The falsely elevated anti-Tg values can be identifiedby measuring the formation of Tg-[^I25I]anti-Tg complexes in thesupernatant of the anti-Tg assay (supernatant assay). For screening purposes, we modified the original anti-Tg RIAinto a solid phase, sandwich-type RIA. Anti-Tg in serum orstandard is first bound to plastic cups coated with Tg and thenquantitated by binding of [¹²⁵I]Tg. This assay has a detectionlimit of 2 U%ml serum, intra- and interassay coefficients ofvariation of 9-15%, and a normal range of J ClinEndocrinol Metab49: 565, 1979)