Clinica Chimica Acta, 212 (1992) 153-154 0 1992 Elsevier Science Publishers B.V. All rights reserved.
153 0009-8981/92/$05.00
CCA 05431
Letter to the Editor
Antibodies to thyroid hormone analogues (Received
10 September
1992; accepted
18 September
1992)
Dear Editor, Sakata et al. reported a case of Hashimoto’s thyroiditis in a 16-year-old female who although being hypothyroid had an inappropriately increased serum FT3 concentration measured by two analogue FT3 methods (Amerlex M-FT3, Amersham International, Tokyo and DPC FT3, Nippon DPC Corporation, Tokyo) [l]. They further stated that interference also occurred in analogue FT4 methods from both these companies and that FT, and FT4 values measured by these RIA kits were proportional with titres of anti-thyroid hormone analogue antibodies, although these data were not presented. In their last paragraph, they state that ‘nobody so far has reported the presence of anti-analogue thyroid hormone antibodies with undetectable thyroid hormone autoantibodies’. This is incorrect as we have already published data on patients with this phenomenon. In our own study reported in 1990, of 47 subjects with antibody interference in analogue FT4 and FT, assays, eight patients were studied in greater detail and of these we identified two subjects who demonstrated this effect [2]. Although their sera showed increased binding of radiolabelled analogues of T4 and T3 (44% and 38%, respectively) there was no increased binding of ‘251-T4or 1251-T3,respectively. The patient with increased binding of radiolabelled T4 analogue was a female with a non-toxic goitre who had been treated by a thyroidectomy and 1311and was receiving 200 pg of T4 per day. In her case, despite using a highly sensitive enzyme linked immunosorbent assay, we could not demonstrate the presence in her serum of antibody to thyroglobulin or thyroid peroxidase. Using the Amerlex-M FT4 method, her measured FT4 concentration was spuriously increased to > 124 pmol/l (reference range 8-26 pmol/l) due to excess binding to her serum of radiolabelled analogue to T4 of 44% (normal binding
153 0009-8981/92/$05.00
CCA 05431
Letter to the Editor
Antibodies to thyroid hormone analogues (Received
10 September
1992; accepted
18 September
1992)
Dear Editor, Sakata et al. reported a case of Hashimoto’s thyroiditis in a 16-year-old female who although being hypothyroid had an inappropriately increased serum FT3 concentration measured by two analogue FT3 methods (Amerlex M-FT3, Amersham International, Tokyo and DPC FT3, Nippon DPC Corporation, Tokyo) [l]. They further stated that interference also occurred in analogue FT4 methods from both these companies and that FT, and FT4 values measured by these RIA kits were proportional with titres of anti-thyroid hormone analogue antibodies, although these data were not presented. In their last paragraph, they state that ‘nobody so far has reported the presence of anti-analogue thyroid hormone antibodies with undetectable thyroid hormone autoantibodies’. This is incorrect as we have already published data on patients with this phenomenon. In our own study reported in 1990, of 47 subjects with antibody interference in analogue FT4 and FT, assays, eight patients were studied in greater detail and of these we identified two subjects who demonstrated this effect [2]. Although their sera showed increased binding of radiolabelled analogues of T4 and T3 (44% and 38%, respectively) there was no increased binding of ‘251-T4or 1251-T3,respectively. The patient with increased binding of radiolabelled T4 analogue was a female with a non-toxic goitre who had been treated by a thyroidectomy and 1311and was receiving 200 pg of T4 per day. In her case, despite using a highly sensitive enzyme linked immunosorbent assay, we could not demonstrate the presence in her serum of antibody to thyroglobulin or thyroid peroxidase. Using the Amerlex-M FT4 method, her measured FT4 concentration was spuriously increased to > 124 pmol/l (reference range 8-26 pmol/l) due to excess binding to her serum of radiolabelled analogue to T4 of 44% (normal binding
