CASE REPORTSReactive thrombocytosis accompanying subclinical hypothyroidism due to Hashimoto's thyroiditisBeyan, Cengiz; Kaptan, KürşatAuthor Information Department of Hematology, Gulhane Military Medical Academy, Ankara, Turkey Correspondence to Professor Cengiz Beyan, MD, Gulhane Military Medical Academy, Department of Hematology, Etlik, 06018 Ankara, TurkeyTel: +90 312 304 4103; e-mail: firstname.lastname@example.org,email@example.com Received 22 November, 2012 Revised 19 February, 2013 Accepted 20 February, 2013 Blood Coagulation & Fibrinolysis: September 2013 - Volume 24 - Issue 6 - p 649-651 doi: 10.1097/MBC.0b013e32836069f5 Buy Metrics Abstract The important thing in a patient in whom platelet values were detected to be greater than normal is whether thrombocytosis is a reactive phenomenon due to a different pathology or due to a clonal hematological pathology. In this case report, reactive thrombocytosis observed in a case with subclinical hypothyroidism due to Hashimoto's thyroiditis is reported; and according to our literature review, this is the first reported case of reactive thrombocytosis due to Hashimoto's thyroiditis and/or subclinical hypothyroidism. A 31-year-old man without any complaint was admitted to the Hematology Department for thrombocytosis which was detected in his routine follow-up. He had been using thyroid hormone replacement for 2 years because of hypothyroidism as Hashimoto's thyroiditis was earlier diagnosed. Due to miscommunication, he stopped his medication levothyroxine 0.1 mg/day 2 weeks in advance and he was still off-drug on admission. Platelet count was 715 × 109/l in the first admission center. Subclinical hypothyroidism diagnosis was made with the present findings and thyroid hormone replacement therapy was again commenced gradually. Platelet counts and thyroid-stimulating hormone value were normal 6 weeks later. As a result, before making diagnosis of thrombocytosis related to myeloproliferative disease or myelodysplastic syndromes, secondary causes should be investigated carefully. Copyright © 2013 YEAR Wolters Kluwer Health, Inc. All rights reserved.