From the Guidelines
Yes, it is possible to have low serum iron but normal serum ferritin, a condition often referred to as functional iron deficiency. This occurs when iron is adequately stored in the body, as reflected by normal ferritin levels, but isn't being properly mobilized for use in red blood cell production 1. According to the NKF-K/DOQI clinical practice guidelines, functional iron deficiency can result when there is a need for a greater amount of iron to support hemoglobin synthesis than can be released from iron stores, despite adequate iron stores being present 1.
Key points to consider in this condition include:
- The distinction between absolute and functional iron deficiency is crucial, with absolute iron deficiency indicating depleted iron stores and functional iron deficiency indicating a need for more iron than can be released from stores 1.
- Serum ferritin levels reflect storage iron, while transferrin saturation (TSAT) reflects iron readily available for erythropoiesis 1.
- A TSAT of < 20% may indicate iron deficiency, but it is not an accurate discriminator between patients who are or are not iron deficient, as some patients with a TSAT > 20% may still be iron deficient 1.
- Treatment of functional iron deficiency depends on the underlying cause, such as addressing inflammation or other conditions interfering with iron utilization, rather than simply supplementing iron 1.
In clinical practice, evaluating iron status involves looking at multiple markers, including serum iron, ferritin, total iron binding capacity (TIBC), and transferrin saturation, to get a complete picture of a patient's iron status 1. It is essential to consider the underlying cause of low serum iron with normal serum ferritin, as treatment should be tailored to address this cause rather than just supplementing iron.
From the Research
Iron Status and Serum Ferritin
- Serum ferritin is often used as a marker of iron status, but it can also be an inflammatory marker 2.
- In patients with chronic kidney disease, serum ferritin levels above 500 ng/ml, especially in conjunction with low iron saturation, are associated with inflammation rather than iron status 2.
- Functional iron deficiency can occur even with serum ferritin levels above 200 microg/l, especially when transferrin saturation is low 3.
Differentiating Iron Deficiency Anemia from Anemia of Chronic Disease
- A combination of serum ferritin and transferrin saturation can be used to differentiate between iron deficiency anemia and anemia of chronic disease 4.
- Log ferritin and transferrin/log ferritin may be promising new parameters in diagnosing iron deficiency anemia, but their use in inflammatory diseases is still limited 4.
- Transferrin saturation can be used as a diagnostic criterion for iron deficiency, especially in patients with chronic inflammatory diseases 5.
Diagnosis of Iron Deficiency and Iron Deficiency Anemia
- Complete blood count (CBC) parameters, such as red blood cell count, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin concentration, and mean corpuscular hemoglobin, can be used to diagnose iron deficiency anemia 6.
- However, the diagnostic capability of CBC parameters in discriminating iron deficiency is still limited, and further studies are needed to elucidate its utility 6.
- Serum ferritin remains a key marker for diagnosing iron deficiency, and its combination with other parameters, such as transferrin saturation, can improve diagnostic accuracy 2, 3, 4, 5.