Serum thyroglobulin: an early indicator of autoimmune post-partum thyroiditis.

OBJECTIVE

The aim of this study was to assess whether autoimmune thyroid damage in post-partum thyroiditis was accompanied by a significant rise in the concentration of thyroglobulin in the serum and whether its measurement could be useful in the prediction of the risk and severity of an episode of post-partum thyroid dysfunction.

PATIENTS

Fifty-one women, who had taken part in a larger survey of post-partum thyroiditis, were selected at random for this study. Fourteen women without elevated circulating thyroid autoantibodies and 21 with raised thyroid autoantibodies remained euthyroid throughout the post-partum year. A third group of 14 women had raised thyroid autoantibody levels and showed one or more episodes of thyroid dysfunction during the course of the first year post partum.

MEASUREMENTS

Thyroid autoantibodies were measured by ELISA, free T3 and free T4 by the Amerlex M method and TSH by an immunoradiometric method. Serum thyroglobulin was measured by a method free from interference by circulating endogenous thyroglobulin autoantibodies. Thyroid ultrasonography was performed using a General Electric RT3600 scanner operating at 7.5 MHz.

RESULTS

Fourteen control women had a mean serum thyroglobulin concentration of 3.3 micrograms/l (SD 4.4; range < 1-12 micrograms/l; 95% confidence interval up to 6.0 micrograms/l). Twenty-one thyroid autoantibody positive euthyroid women had a mean serum thyroglobulin level of 5.8 micrograms/l (SD 6.2; range < 1-36 micrograms/l) which was not significantly different from that seen in the control group. Sixteen thyroid autoantibody positive women who showed one or more episodes of thyroid dysfunction during the post-partum period had a mean serum thyroglobulin of 31 micrograms/l (SD 24.8; range up to 88 micrograms/l) and this was significantly elevated compared with both the control and antibody positive groups (P < 0.001). Serum thyroglobulin concentrations at 3 months post partum correlated with the degree of post-partum hypothyroidism (as indicated by the maximum TSH and the minimum free thyroxine concentrations post partum) and, in those cases where thyroid ultrasound examinations were performed, with the degree of lymphocytic infiltration of the thyroid gland.

CONCLUSIONS

The data presented in this paper confirm the destructive nature of post-partum thyroiditis and indicate that the measurement of serum thyroglobulin concentration could assist in the identification of those women at risk of post-partum thyroiditis.