title: Erythrocytosis associated with hyperthyroidism: a rare case report and clinical study of possible mechanism.
abstract: OBJECTIVE
  To report a rare case of erythrocytosis that occurred in close association with Graves' hyperthyroidism. In order to explore the role of altered erythropoiesis in hyperthyroidism, factors related to erythropoiesis were studied in 30 patients with Graves' hyperthyroidism.
  
  
  METHODS
  The relationship between thyroid hormone level and erythrocytosis was studied in a patient with Graves' hyperthyroidism and erythrocytosis. Later, 30 consecutive patients with proven untreated Graves' hyperthyroidism and 30 age- and sex-matched healthy controls were recruited. All patients received methimazole therapy. Erythrocyte indices, thyroid function, serum erythropoietin (EPO), and hypoxia-inducible factor-1α (HIF-1α) concentrations were measured before and after eight weeks of therapy.
  
  
  RESULTS
  In our case study, erythrocytosis relapsed with elevation of thyroid hormones. Methimazole or subsequent radioiodine therapy reduced the conditions of erythrocytosis and thyroid function returned to normal. In the clinical study, erythrocyte counts, serum erythropoietin, and HIF-1α levels in the hyperthyroid group were significantly higher than those in the control subjects. All subjects were grouped together for correlation analyses and HIF-1α was shown to correlate with total triiodothyronine (TT(3)), total thyroxine (TT(4)), and EPO levels. The correlation between EPO and TT(3) or TT(4) approached significance. After eight weeks of anti-thyroid drug therapy, a small but statistically significant increase in hemoglobin and erythrocyte count with a significant decrease in HIF-1α and EPO level was seen in hyperthyroid subjects.
  
  
  CONCLUSIONS
  Erythrocytosis may appear in patients with hyperthyroidism, and one possible mechanism is thyroid hormone-induced augmentation of HIF-1α, resulting in increased EPO levels.
authors.affiliation: a Department of Endocrinology , First Hospital Affiliated to Medical College of Xi'an Jiaotong University , Xi'an , P.R. China.
authors.forename: Xingjun
authors.initials: X
authors.lastname: Liu
authors.affiliation: a Department of Endocrinology , First Hospital Affiliated to Medical College of Xi'an Jiaotong University , Xi'an , P.R. China.
authors.forename: Jingfang
authors.initials: J
authors.lastname: Liu
authors.affiliation: a Department of Endocrinology , First Hospital Affiliated to Medical College of Xi'an Jiaotong University , Xi'an , P.R. China.
authors.forename: Liya
authors.initials: L
authors.lastname: Fan
authors.affiliation: a Department of Endocrinology , First Hospital Affiliated to Medical College of Xi'an Jiaotong University , Xi'an , P.R. China.
authors.forename: Bingyin
authors.initials: B
authors.lastname: Shi
mesh_terms: D000293:Adolescent; D000328:Adult; D013956:Antithyroid Agents / Q000008:administration & dosage / Q000494:pharmacology*; D004921:Erythropoietin / Q000097:blood*; D005260:Female; D006111:Graves Disease / Q000097:blood / Q000150:complications / Q000188:drug therapy; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000097:blood* / Q000187:drug effects; D008297:Male; D008713:Methimazole / Q000008:administration & dosage / Q000494:pharmacology*; D008875:Middle Aged; D011086:Polycythemia / Q000097:blood / Q000188:drug therapy / Q000209:etiology; D055815:Young Adult
chemical_list: D013956:Antithyroid Agents; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D004921:Erythropoietin; D008713:Methimazole
keywords: EPO; Erythrocytosis; HIF-1α; hyperthyroidism