Relationship between Thyroid Function and Platelet Counts

Yasuyuki Endo, MD, Akita University School of Medicine, 1-1-1, Hondo Akita 010 (Japan) I read with interest the article on thrombocytope-nia in Graves’ disease which appeared in Acta Haem-atologica 63:185–190 (1980). According to it, thyroid hormone stimulates the reticuloendothelial system (RES) resulting in thrombocytopenia. However, since I have not clinically experienced patients with hyper-thyroidism associated with thrombocytopenia except for the complication of idiopathic thrombocytopenic purpura [1] and have noticed the statement ‘Platelets are normal in thyroid disease’ in a classic endocrino-logical treatise [2], I tried to examine platelet counts in patients with both hyperand hypothyroidism whom I myself had diagnosed and treated from 1981 to 1985, because I thought there was a great difference in the levels of thyroid hormones between these two conditions. I determined platelet counts by ELT-8 (Or-tho, USA) when I saw the patients for the first time and during their course, and used Student’s t test by calculating the difference between matched pairs for statistical analysis. The platelet counts of 30 patients with hyperand hypothyroidism are shown in table I. I could not discover any significant difference between the two conditions. When observed individually, platelet counts hardly changed following the change of thyroid function, but seemed invariable (table II). In addition, I noted the tendency for platelet counts to decrease with age. Thus, I think that, although it is true that thyroid hormone stimulates RES resulting in a shortening of platelet survival, the bone marrow function producing platelets is compensated for soon and marked thrombocytopenia does not appear. There is a study in which the increase of megakaryocytes in the bone marrow of patients with hyperthyroidism was reported [3]. It is said that the spleen is palpable in 30% of the patients with hyperthyroidism [4], but in Table I. Platelet counts in hyperand hypothyroidism (1981–1985) HyperSex Age Platelets HypothySex Age Plateletsthyroidism (×104/μl) roidism (×lOVμl)