LAKE BUENA VISTA, FLA. – Between 30% and 50% of hypothyroid patients with persistent symptoms despite adequate levothyroxine therapy may have covert iron deficiency, findings from a small study suggest.
The findings cast “a dark shadow of doubt on the validity of the studies on the effect of T3 therapy in these patients,” Dr. Esa Soppi reported in a poster at the International Thyroid Congress.
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Study subjects were women with a history of overt hypothyroidism who had persistent symptoms after appropriate and ongoing treatment with L-T4. L-T4 dosing was adjusted as necessary to achieve a thyroid-stimulating hormone concentration of 1-2 mU/L, and diabetes, B12-vitamin deficiency, celiac disease, hypercalcemia, and vitamin D deficiency were ruled out as causes for the persistent symptoms.
Further, none of the patients had anemia, and red cell indices were within the reference range.
Five of the women had serum ferritin of less than 15 mcg/L, and two of those had serum iron, transferrin, or soluble transferrin receptor concentration or transferrin saturation out of range, suggesting iron deficiency. The remaining 20 women had a serum ferritin concentration between 15 mcg/L and 60 mcg/L, Dr. Soppi of Eira Hospital, Helsinki, noted at the meeting held by the American Thyroid Association, Asia-Oceania Thyroid Association , European Thyroid Association, and Latin American Thyroid Society.
Four of the five women with serum ferritin less than 15 mcg/L, and 14 of the 20 with less than 15-60 mcg/L became symptom free when treated with oral iron substitution therapy for 6-12 months, Dr. Soppi said.
“All patients were advised to take their thyroxine dose at the fasting state in the morning and start breakfast 30 minutes later. The interval between the iron and thyroxine was at least 4 hours. The response was observed at a serum ferritin concentration approaching 70-100 mcg/L,” Dr. Soppi wrote, noting that in one patient – a 28-year-old woman with type 1 diabetes and hypothyroidism – all symptoms of fatigue, failure to thrive, and lethargy experienced before the start of the iron therapy disappeared after about 4 months of oral iron therapy at a dose of 100 mg twice daily.
However, another patient – an 18-year-old woman with hypothyroidism after total thyroidectomy performed because of a suspected thyroid malignancy – was found to have no malignancy; disabling tiredness, and failure to thrive emerged after the thyroidectomy and persisted despite iron therapy given at 100 mg twice daily.
“Iron deficiency is as common as hypothyroidism and its symptoms resemble those of hypothyroidism. However, the diagnosis of iron deficiency without anemia is extremely challenging since all indicators of iron status may be ‘normal.’ A clinical suspicion is key to diagnosis of covert iron deficiency,” Dr. Soppi wrote, noting that the serum ferritin concentration may be helpful, and restoration of ferritin above 100 mcg/L seems to ameliorate symptoms in about two-thirds of patients, and that it is not currently known why some iron-deficient patients fail to respond to restoration of their functional iron stores.