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Excerpt from nih article above

Thyroid disorders are frequently accompanied by red blood cell

abnormalities. Thyroid hormones often have important eﬀect on

erythropoiesis. They enhance erythropoiesis through hyper proliferation of

immature erythroid progenitors and increase secretion of erythropoietin

(EPO) by inducing erythropoietin gene expression. Thyroid hormones also

augment repletion of hypoxia inducible factor1 (HIF-1) and then motivate

growth of erythroid colonies (BFU-E, CFU-E).These hormones also intensify

erythrocyte 2, 3 DPG compactness, which enhances the delivery of oxygen

to tissues. Hyperthyroidism causes mild decreases in total white blood cell

count, neutropenia, thrombocytopenia and increases, normal or mild

decreases in total white blood cell count. Generally it seems that

hypothyroidism causes hypoplasia in all myeloid cell lineages and

hyperthyroidism result in hyperplasia. With regard to lymphocytes, T3 is as

a precursor substance for normal B cell formation in bone marrow through

its mediation of pro-B cell proliferation. Therefore, thyroid disorders can

induce diﬀerent eﬀects on various blood cell lineages (7-10).

Hypothyroidism can cause various forms of anemia (normochromic-

normocytic, hypochromic-microcytic or macrocytic) through reducing the

oxygen metabolism. Microcytic anemia generally attribute to malabsorption

of Iron and loss of Iron by menorrhagia, whereas, macrocytic anemia causes

or induces malabsorption of vitamin B12 , folate, pernicious anemia and

insuﬀicient nutrition (10).

On the other hand, anemia frequently is not seen in patients with

hyperthyroidism, while there were erythrocytosis in this situation, but when

anemia present, may be morphologically similar to that observed in

hypothyroidism. Patients with hypothyroidism have a decreased erythrocyte

mass due to reduction of plasma volume and may undetectable by routine

measurement such as hemoglobin concentration, whereas an increased

erythrocyte mass is observed in most hyperthyroid patients (11-12) .

Alteration in other hematological parameters such as hemoglobin (HG),

hematocrit (HCT), mean corpuscular volume (MCV) ,mean corpuscular

hemoglobin (MCH), white blood cell (WBC) count and platelet count is

associated with thyroid dysfunction is observed as well (9), but all changes

return to normal if an euthyroid (normal) state is obtained. Pancytopenia is

a rare side eﬀect of that its cause is not well understood. Immunological

mechanisms have been oﬀered for decline of the life-span of erythrocytes

and platelets (13).Because of high prevalence of thyroid dysfunctions in

Iranian population, we attempted in the present study to evaluate the eﬀect

of thyroid dysfunctions particularly cells and red blood cells indices.

Conclusion

Thyroid dysfunctions have a direct eﬀect on most red blood cells indices and

these changes should be considered by medical care provider.