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THE MEASUREMENT OF SERUM THYROGLOBULIN IN THE PRESENCE OF THYROGLOBULIN ANTIBODIES
Author(s) -
RATCLIFFE J. G.,
AYOUB L. A. W.,
PEARSON D.
Publication year - 1981
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1981.tb00695.x
Subject(s) - thyroglobulin , euthyroid , chemistry , radioimmunoassay , medicine , endocrinology , antibody , thyroid , immunology
SUMMARY In a significant proportion of patients with thyroid disorders, thyroglobulin antibodies (TgAb) invalidate double‐antibody radioimmunoassays (RIA) for thyroglobulin (Tg). A modified RIA procedure for determining serum Tg in the presence of TgAb, is described. Two measurements are made on each sample.aRatio of immunoglobulin (Ig)‐bound thyroglobulin to free thyroglobulin (bound:free ratio). This is measured by the distribution of a trace quantity of 125 I‐Tg between bound and free fractions.bConcentration of free, i.e. unbound thyroglobulin. This is measured in the supernatant after precipitation of IgG‐bound Tg.Then, bound Tg = B:F x (free Tg) and total Tg = (bound Tg) + (free Tg). Critical factors examined in the validation of the modified method were: (1) use of immunologically intact 125 I‐Tg (specific activity ± 5 mCi/mg); (2) equilibration of tracer Tg with endogenous serum Tg, and (3) clean separation of IgG‐bound and free fractions of Tg with goat anti‐human IgG. Recovery of added Tg in the presence of TgAb was 105% and interassay precision of total Tg assay was ≤ 9·3%. In euthyroid subjects without TgAb, the correlation between total Tg levels by the modified and standard double‐antibody method was 0·931. The correlation was much poorer in the presence of TgAb (r = 0·752) reflecting their interference in the standard method. Reference ranges for serum total Tg levels by the modified method in euthyroid, hyper‐and hypothyroid subjects with and without TgAb are detailed.