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Thyroglobulin IRMA Pasteur Immunoassay: Sensitivity of the Assay and Interference from Thyroglobulin Autoantibodies

¹ Sanofi Diagnostics Pasteur, ZI du Léopha, rue d'Italie, 69780 Mions, France,
² CNRS UMR 9921, Faculté de Pharmacie, 34060 Montpellier Cedex 1, France
^a author for correspondence.

To the Editor:

In light of the recent article by Spencer et al. (1) as well as the editorial by Spencer (2), we feel obliged to clarify a few points concerning the performance of our thyroglobulin (Tg) immunoassay and make some more general comments.

In Fig. 1 of ref. 1, the legend reads "Serum Tg values measured by six different Tg methods." The six assays tested are clearly indicated in the legend but only four of them appear in the Figure. The one from our group, Tg IRMA Pasteur, is missing.

Surprisingly, the "relative sensitivities of the five different Tg methods as judged by the response in signal cpm," shown in Fig. 2 of ref. 1, are expressed as absolute signals given by the bound (B) antibody tracer (background subtracted). When antibodies are labeled with radioisotopes that have a relatively short half-life, the results should preferably be expressed as the bound fraction (B/B0) to take into account radioactive decay. In our case (the Sanofi Diagnostics Pasteur test has a ¹²⁵I label), the difference between the two modes of representation is particularly striking because the assay was performed approximately at the expiration date of the tracer. All evaluations of our Tg immunoassay, without fail, underlined the very high analytical sensitivity of our assay due to the use of a selected combination of antibodies.

Furthermore, Mariotti et al. (3) were cited in ref. 1 as having defined the true minimum detectable concentration of Tg at 1.5 µg/L with the Tg IRMA Pasteur assay. We demonstrated, however, that a cutoff of 1 µg/L gives the best results in terms of clinical accuracy (4). This value is significantly higher than the minimum detectable concentration defined at the confidence limit of 95% for the calibration . . . [Full Text of this Article]

References

Carole A. Spencer and Michael Takeuchi

General Clin. Research Center 6602, Dept. of Medicine, Univ. of Southern California, 2025 Zonal Ave., Los Angeles, CA 90033
^a author for correspondence.

To the Editor:

References

The following articles in journals at HighWire Press have cited this article:

				F. Pacini, E. Molinaro, M. G. Castagna, L. Agate, R. Elisei, C. Ceccarelli, F. Lippi, D. Taddei, L. Grasso, and A. Pinchera Recombinant Human Thyrotropin-Stimulated Serum Thyroglobulin Combined with Neck Ultrasonography Has the Highest Sensitivity in Monitoring Differentiated Thyroid Carcinoma J. Clin. Endocrinol. Metab., August 1, 2003; 88(8): 3668 - 3673. [Abstract] [Full Text] [PDF]