From the Guidelines
Low iron binding capacity is not typically due to iron deficiency anemia, but rather is often associated with conditions such as hemochromatosis, chronic inflammatory states, malnutrition, or liver disease. According to the study by the Centers for Disease Control and Prevention 1, Total Iron Binding Capacity (TIBC) is a measure of the iron-binding capacity within the serum and reflects the availability of iron-binding sites on transferrin. The study found that TIBC increases when serum iron concentration (and stored iron) is low and decreases when serum iron concentration (and stored iron) is high. Some key points to consider when interpreting TIBC results include:
- Factors other than iron status can affect TIBC readings, such as inflammation, chronic infection, malignancies, liver disease, nephrotic syndrome, and malnutrition, which can lower TIBC readings 1.
- Oral contraceptive use and pregnancy can raise TIBC readings 1.
- TIBC is less sensitive to iron deficiency than is serum ferritin concentration, because changes in TIBC occur after iron stores are depleted 1. In clinical practice, a low iron binding capacity on laboratory tests should prompt further evaluation to determine the underlying cause, as it is unlikely to be due to iron deficiency anemia.
From the Research
Iron Deficiency Anemia and Low Iron Binding Capacity
- Low iron binding capacity is related to iron deficiency anemia, as it is a key indicator in the diagnosis of this condition 2, 3.
- Iron deficiency anemia is defined as low hemoglobin due to low iron stores, and it affects approximately 1.2 billion people worldwide, including 10 million in the US 2.
- The diagnosis of iron deficiency anemia is typically made by measuring serum ferritin and/or transferrin saturation, with a transferrin saturation of less than 20% indicating iron deficiency 2.
- Total Iron Binding Capacity (TIBC) is also used in the diagnosis of iron deficiency, with high TIBC levels indicating iron deficiency 3.
- However, studies have shown that serum iron and TIBC may not be reliable indicators of iron deficiency, especially in certain populations such as the elderly 4, 3.
Diagnostic Accuracy of Serum Iron and TIBC
- A study found that serum iron and TIBC had low sensitivity and specificity for diagnosing iron deficiency anemia, and that these tests were redundant if serum ferritin was available 3.
- Another study found that in elderly subjects, iron deficiency anemia may develop with higher levels of serum ferritin, making the conventional cutoff for serum ferritin not appropriate for this population 4.
- The diagnostic accuracy of serum iron and TIBC may be affected by various factors, including age, comorbidities, and inflammatory conditions 2, 4, 3.
Evaluation of Suspected Anemia
- When anemia is suspected, a thorough history and physical examination, as well as a complete blood cell count (CBC), are essential for initial evaluation 5.
- Supplemental tests, such as a peripheral blood smear, reticulocyte count, iron panel, and levels of vitamin B12 and folate, may be necessary to determine the cause of anemia 5.
- The evaluation of suspected anemia should include an assessment of iron stores, including serum ferritin and transferrin saturation, to diagnose iron deficiency anemia 2, 5.