The endocrine system influences homeostasis of virtually every tissue. Thus, it is not unexpected that it also influences hematopoiesis. However, the effect of the endocrine disequilibrium is principally on erythropoiesis with limited impact on leukocytes, platelets and hemostasis. Thus, anemia is the most common hematopoietic abnormality in endocrine disorders and may be the first manifestation of an endocrine disorder. Erythrocytosis is less common but occurs in certain endocrine disorders. The pathophysiologic basis of the anemia is often multifactorial, but a direct influence of hormones on erythropoiesis in some instances may contribute to anemia. A decreased plasma volume in some of these disorders may mask the severity of anemia. Some endocrine disorders are associated with an impaired response to the therapeutic use of erythropoietin.
Acronyms and Abbreviations
BFU-E, burst-forming unit erythroid; CFU-E, colony forming-unit erythroid; EGLN1, gene encoding proline hydroxylase-2; EGLN2, gene encoding proline hydroxylase-1; EPAS1, gene encoding HIF2α; EPIC-Norfolk, European Prospective Investigation of Cancer-Norfolk; HIF, hypoxia-inducible factor; RTHα, resistance to THα; TH, thyroid hormone; THRA, gene encoding thyroid hormone receptor α; THRB, gene encoding thyroid hormone receptor β; TRs, thyroid hormone receptors, TRα, thyroid hormone receptor alpha; TSH, thyroid stimulating hormone.
THYROID DYSFUNCTION AND INCIDENCE OF ANEMIA
Anemia is a well-recognized complication of thyroidectomy1 and is associated with hypo- and hyperthyroidism and subclinical thyroid dysfunction. However, the exact frequency of anemia, as well as any causative relationship between thyroid dysfunction and anemia, are not defined.2–5 In a retrospective review of 412 patients, anemia defined as a hemoglobin less than 130 g/L in men and less than 120 g/L in women was present in 57% of patients with hypothyroidism and 41% of those with hyperthyroidism.2 Another study found anemia in 43% of an overt group of patients with hypothyroid and 39% in a set of subclinical patients with hypothyroid; however, 26% of the control group also had anemia.3 A cohort population–based study conducted by the European Prospective Investigation into Cancer-Norfolk (EPIC-Norfolk) of more than 8000 participants, which excluded patients with anemia attributed to chronic kidney disease, inflammation, or iron deficiency, found the highest prevalence of anemia in overt hyperthyroidism (14.6%) compared with 7.7% in overt hypothyroidism and no increase in anemia in those with subclinical hypo- or hyperthyroidism.4 A subsequent meta-analysis of individual participant data from 16 cohorts (including the EPIC-Norfolk study) found an increased risk of anemia in all categories of abnormal thyroid status compared with euthyroid participants.5 The odds ratio was 1.84 for overt hypothyroidism, 1.69 for overt hyperthyroidism, 1.21 for subclinical hypothyroidism, and 1.27 for subclinical hyperthyroidism.
The anemia in hypothyroidism has been described variably as normocytic, macrocytic, or microcytic1; coexisting deficiencies of iron, cobalamin (vitamin B12), and folate (Chaps. 42 and 44) may explain ...