European interlaboratory comparison of serum thyroglobulin measurement.

A European interlaboratory comparison of serum thyroglobulin measurements was performed after an initiative from the European Organization of Research and Therapy of Cancer. Fifty-two laboratories were addressed and 45 of these (83%) participated in the study by measuring serum thyroglobulin and its autoantibody in 5 thyroglobulin containing sera. Thyroglobulin antibodies were added to two of the sera. Two commercial kits were used by a large number of the laboratories (11 and 8, respectively). Each kit showed a reasonably low interlaboratory coefficient of variation at concentrations above 25 micrograms/l, but with discrepancy between the methods. The remaining miscellaneous methods (24) showed a variation above 65% in all samples. In all laboratories the addition of thyroglobulin antibodies resulted in false thyroglobulin measurements with either elevated or depressed levels. It is concluded that a reference calibrator for serum thyroglobulin is strongly needed as the first essential step towards interlaboratory standardization of serum thyroglobulin, thereby opening a possibility for multicentre studies of its value in the post-therapy follow-up of patients with differentiated thyroid carcinoma.