[Detection of thyroglobulin autoantibodies and potential interference with serum thyroglobulin measurement]

Thyroglobulin measurement is useful for the follow up of patients subjected to total thyroidectomy for differentiated thyroid carcinoma. Thyroglobulin autoantibodies may interfere with its determination.

To measure thyroglobulin autoantibodies and their interference with thyroglobulin determination.

The presence of thyroglobulin autoantibodies was investigated in 801 serum samples sent to the laboratory for measurement of thyroglobulin levels. A serum was considered positive for these autoantibodies when radioactivity corresponding to 125I-thyroglobulin bound to thyroglobulin autoantibodies, precipitated with human gamma globulin, exceeded in 1.4 times that of a negative sera pool. In positive sera, thyroglobulin autoantibody concentration was measured and its interference with thyroglobulin radioimmunoassay was assessed through a recuperation test using exogenous thyroglobulin.

Thyroglobulin autoantibodies were detected in 149 sera (18.6%). Of these, 65 had a recuperation that fluctuated between 1 and 80%. Thyroglobulin autoantibody concentration was negatively correlated with recuperation percentages (r = -0.64; p < 0.001) but not with thyroglobulin concentrations (r = 0.08). Thyroglobulin was higher in positive sera with a recuperation over 80% than in sera with a recuperation of less than 80% (12.7 +/- 1.7 and 5.9 +/- 0.6 ng/ml, respectively; p < 0.001).

Thyroglobulin autoantibodies interfere with thyroglobulin measurement by radioimmunoassay, sequestering variable amounts of thyroglobulin. The presence of these autoantibodies must be investigated prior to thyroglobulin determination.