Patients with iron deficiency anemia might need treatment for subclinical hypothyroidism

Iron deficiency anemia did not respond to oral iron therapy in patients with subclinical hypothyroidism.

Subclinical hypothyroidism should be treated in patients with iron deficiency anemia when both conditions exist, as it may provide a desired therapeutic response to oral iron replacement.

Researchers randomly assigned 51 patients with coexisting iron deficiency anemia and subclinical hypothyroidism to 240 mg per day of oral iron alone or 240 mg per day of oral iron plus 75 mcg per day of levothyroxine. Measurements were taken for hemoglobin, hematocrit, red blood cell count, serum iron levels, ferritin, total iron-binding capacity, thyroid-stimulating hormone and free thyroxine.

Iron therapy alone insufficient

Addition of levothyroxine resulted in improvement of serum iron and blood count variables, according to the study.

“These findings support our clinical observation regarding the presence of a group of patients resistant to oral iron because of their coexisting subclinical hypothyroidism,” they wrote. “These patients might benefit from addition of levothyroxine to their treatment regimen, and this might be an indication for treating subclinical hypothyroidism in iron deficiency anemia patients.”

In the iron group, mean hemoglobin levels increased by 0.4 g/dL (95% CI, 0.2-0.7) compared with the iron/levothyroxine group (1.9 g/dL; 95% CI, 1.5-2.3). Serum iron was greater by a mean of 47.6 mcg/dL (95% CI, 34.5-60.6) in the iron/levothyroxine group, according to the researchers.

Hemoglobin, red blood cells, hematocrit and serum ferritin levels were greater in the iron/levothyroxine group after treatment (P<.0001). A negative correlation was observed for starting hemoglobin and an increase in hemoglobin in the iron/levothyroxine group (P=.006).

The endemic goiter region had a high prevalence of both disorders, indicating the benefit of treating subclinical hypothyroidism, according to the researchers. “Resistance to oral iron treatment indicates the need to test for thyroid function, especially in regions with endemic goiter,” they wrote. – by Christen Haigh

J Clin Endocrinol Metab. 2009;94:151-156.

In my experience, the combination of subclinical hypothyroidism and iron deficiency anemia is very uncommon. Although the results in this study are impressive and will alter my practice, I found their therapeutic regimen to be paradoxical, namely a capsule containing 80 mg ferrous sulfate and 25 mcg levothyroxine given twice a day. Ferrous sulfate is known to bind thyroxine and prevent its absorption. This may account for the modest decrease in mean TSH which fell from 7.4 to 3.4 mU/L in patients with iron deficiency. Nevertheless, to correct the anemia, should we administer the levothyroxine with ferrous sulfate rather than separate them by more than eight hours, as has been my practice?

– Jerome M. Hershman, MD

Endocrine Today Editorial Board member