From the Guidelines
Iron supplements should be started when the transferrin saturation is less than 20%, particularly in patients with iron deficiency anemia. This recommendation is based on the most recent and highest quality study available, which suggests that a transferrin saturation below 20% indicates inadequate iron availability for effective erythropoiesis, even if hemoglobin levels haven't yet declined significantly 1.
Key Considerations
- The goal ferritin level is 50 ng/mL, regardless of sex at birth, and iron parameters should not be evaluated within 4 weeks of a total dose infusion (TDI) as the circulating iron interferes with the assay leading to specious results 1.
- A TSAT <20% has high sensitivity for diagnosing absolute or functional iron deficiency, but a ferritin of <100 ng/mL has a low sensitivity of 35%–48% 1.
- Soluble transferrin receptor (sTfR) has been shown to be more sensitive in patients with inflammatory conditions where the ferritin (but not the TSAT) is unreliable for evaluation of iron deficiency and iron deficiency anemia 1.
Treatment Approach
- The typical recommended supplement is ferrous sulfate 325 mg orally 1-3 times daily (providing 65 mg of elemental iron per tablet), taken between meals with vitamin C to enhance absorption.
- Alternative formulations include ferrous gluconate or ferrous fumarate if sulfate is not tolerated.
- Treatment should continue for 3-6 months after hemoglobin normalizes to replenish iron stores.
- Patients should be monitored for side effects such as constipation, nausea, and abdominal discomfort, which can be managed by taking supplements with food (though this reduces absorption) or reducing dosage.
- In cases of severe iron deficiency or intolerance to oral supplements, intravenous iron formulations may be considered 1.
From the Research
Iron Supplementation Guidelines
- The decision to start iron supplements is typically based on transferrin saturation (TSAT) levels, among other factors 2, 3, 4, 5.
- According to current guidelines, iron deficiency is defined by a serum ferritin level <100 ng/ml or a TSAT <20% if the serum ferritin level is 100-299 μg/L 3.
- However, some studies suggest that a TSAT <20% may be a more reliable indicator of iron deficiency, regardless of serum ferritin levels 3, 5.
- In patients with heart failure, a TSAT <20% has been associated with a higher risk of adverse outcomes, including death and hospitalization 3, 5.
Transferrin Saturation Thresholds
- A TSAT threshold of <20% is commonly used to define iron deficiency 2, 3, 4, 5.
- However, some studies suggest that a lower TSAT threshold may be more effective in identifying patients who would benefit from iron supplementation 3, 5.
- The use of TSAT as a diagnostic criterion for iron deficiency has been shown to be beneficial in patients with chronic inflammatory diseases 4.
Clinical Implications
- Iron supplements should be started when TSAT levels fall below 20% 2, 3, 4, 5.
- However, the decision to start iron supplements should be individualized and based on a comprehensive assessment of the patient's iron status and clinical condition 6.
- Regular monitoring of TSAT levels and other markers of iron metabolism is essential to ensure effective and safe iron supplementation therapy 6, 5.