Can hyperthyroidism cause low ferritin levels?

Hyperthyroidism and Ferritin Levels

Hyperthyroidism does not cause low ferritin; instead, it typically causes elevated ferritin levels that normalize with treatment of the hyperthyroid state. 1, 2

The Relationship Between Hyperthyroidism and Ferritin

Hyperthyroidism elevates serum ferritin through direct thyroid hormone effects on ferritin synthesis, not through iron overload. The evidence consistently demonstrates that:

• Serum ferritin levels are increased in hyperthyroid patients and return to normal following antithyroid therapy 1
• This elevation occurs through direct action of thyroid hormones on ferritin synthesis 1
• When hyperthyroid patients achieve euthyroid status, ferritin levels decrease significantly while transferrin levels increase 1, 2

Mechanism of Ferritin Elevation in Hyperthyroidism

The ferritin elevation in hyperthyroidism resembles an acute-phase reaction:

• Thyroid hormones (particularly T3) directly induce hepcidin expression in hepatocytes, which regulates iron metabolism 2
• Hepcidin levels are elevated during hyperthyroidism and decrease when euthyroidism is achieved (particularly evident in males) 2
• This occurs independently of inflammatory markers - studies show no changes in high-sensitivity CRP, procalcitonin, IL-6, IL-1β, or TNF-α between hyperthyroid and euthyroid states 2

Clinical Evidence Against Low Ferritin in Hyperthyroidism

Multiple studies demonstrate the opposite pattern:

• In 13 hyperthyroid patients, mean ferritin levels were elevated and normalized only after achieving euthyroid state through antithyroid therapy 1
• Hemoglobin, red blood cells, and packed cell volume actually increased (not decreased) with antithyroid treatment, indicating improved iron utilization 1
• A large population-based study (SHIP) of 4,111 subjects found no association between thyroid function and low serum ferritin levels in either gender 3

Important Clinical Caveats

When anemia coexists with hyperthyroidism, ferritin may be even more elevated due to impaired iron utilization by erythropoietic cells 1. This represents functional iron deficiency rather than depleted iron stores.

If you encounter a hyperthyroid patient with truly low ferritin (<15 μg/L), investigate alternative causes of iron deficiency:

• Gastrointestinal blood loss (the hyperthyroidism is coincidental) 4
• Menstrual blood loss in premenopausal women 4
• Dietary insufficiency or malabsorption 4
• The low ferritin is not caused by the hyperthyroidism itself

Interpretation Algorithm for Ferritin in Hyperthyroid Patients

If ferritin is elevated (>150 μg/L) in a hyperthyroid patient:

• This is the expected pattern 1, 2
• Ferritin should normalize with treatment of hyperthyroidism 1
• Do not interpret this as iron overload requiring phlebotomy 5

If ferritin is low (<30 μg/L) in a hyperthyroid patient:

• The hyperthyroidism is not the cause 1, 2, 3
• Investigate for gastrointestinal blood loss, particularly if ferritin <15 μg/L 4
• Consider menstrual losses, dietary deficiency, or malabsorption 4
• Treat the iron deficiency independently while managing the hyperthyroidism 4