[Platelet retention and hypothyroidism: an investigation in patients with thyroid carcinoma treated by total thyroidectomy (author's transl)].

Platelet retention was investigated using a standardized technique with a glass pearl column in 18 patients with malignant thyroid disease treated by thyroidectomy before and after high-dose radioiodine treatment (80 or 150 mCi). As compared with the normal controls platelet retention was significantly lower in 13 hypothyroid patients in whom thyroidectomy had been undertaken at least 6 months previously and hormone substitution therapy had been interrupted 3 weeks before the period of investigation. The remaining 5 patients, studied about 18 days following thyroidectomy, were euthyroid and displayed platelet retention values within the lower limits of the normal range except for one patient with markedly reduced values. Thyroid substitution therapy with synthetic preparations induced recovery of platelet retention in both groups examined over a 4 week period, the increase being highly significant in the group of hypothyroid patients. A transient increase in platelet retention was observed 24 hours after a therapeutic dose of radioiodine, and initial values being regained after a further 24-hour period. This phenomenon was found in both, the euthyroid and hypothyroid group, however, it was more pronounced in the latter patients. Our results indicate a dependence of platelet retention on thyroid hormone concentration. The observed transient increase after radioiodine may be due to a radiation effect.