From the Guidelines
Serum ferritin less than 15 ng/L is diagnostic for iron deficiency anemia. This test is the most specific laboratory marker for iron deficiency because ferritin is the primary storage protein for iron in the body, and low levels directly reflect depleted iron stores 1. When iron stores are exhausted, ferritin levels fall before hemoglobin or hematocrit decreases, making it an early and reliable indicator. The other listed tests are not diagnostic for iron deficiency anemia. Serum creatinine greater than 1.7 indicates kidney dysfunction, not iron status. While a hematocrit less than 37 in females indicates anemia, it is not specific to iron deficiency as many conditions can cause low hematocrit. Bilirubinemia (elevated bilirubin) is associated with hemolytic anemias and liver disorders rather than iron deficiency.
Some guidelines suggest using a cutoff of 45 ng/mL for ferritin when diagnosing iron deficiency anemia 1. However, a level of less than 15 ng/L is highly specific for iron deficiency, with a specificity of 0.99 1. For a complete evaluation of iron deficiency anemia, additional tests like hemoglobin, mean corpuscular volume (MCV), transferrin saturation, and total iron-binding capacity (TIBC) are often performed alongside ferritin to confirm the diagnosis and assess severity.
It's worth noting that serum ferritin is an acute phase protein, and apparently normal levels may occur with iron deficiency in the context of an inflammatory disease process 1. Therefore, interpretation of ferritin levels should take into account the clinical context and other laboratory results.
In terms of diagnosis and management, the American Gastroenterological Association (AGA) recommends using a cutoff of 45 ng/mL for ferritin when diagnosing iron deficiency anemia, and suggests bidirectional endoscopy in asymptomatic postmenopausal women and men with iron deficiency anemia 1. However, the most recent and highest quality study suggests that a serum ferritin level of less than 15 ng/L is diagnostic for iron deficiency anemia 1.
Key points to consider when diagnosing iron deficiency anemia include:
- Serum ferritin less than 15 ng/L is diagnostic for iron deficiency anemia
- Other laboratory tests, such as hemoglobin and MCV, can help confirm the diagnosis and assess severity
- Serum creatinine and bilirubin levels are not specific for iron deficiency anemia
- Interpretation of ferritin levels should take into account the clinical context and other laboratory results.
From the Research
Diagnostic Tests for Iron Deficiency Anemia
The following lab tests are diagnostic for iron deficiency anemia:
- Serum ferritin less than 15 ng/L: This is a common diagnostic criterion for iron deficiency anemia, as ferritin levels reflect the body's iron stores 2, 3, 4.
- Other tests mentioned, such as serum CR, hematocrit, and bilirubinemia, are not directly related to the diagnosis of iron deficiency anemia based on the provided evidence.
Serum Ferritin as a Diagnostic Marker
- Serum ferritin is considered the most efficient test for diagnosing iron deficiency anemia 2.
- However, the cutoff value for serum ferritin can vary depending on the population being studied, with some studies suggesting a cutoff value of 22 microg/L for community-dwelling older adults 3 and others suggesting a higher cutoff value of 30 microg/L for detecting iron deficiency 4.
- It is also important to consider the effects of inflammation on serum ferritin levels, as ferritin can increase in response to inflammation regardless of iron stores 5, 4.
Limitations of Other Tests
- Serum CR greater than 1.7 is not a commonly used diagnostic criterion for iron deficiency anemia, and its relevance to this condition is not supported by the provided evidence.
- Hematocrit less than 37 in females is a criterion for anemia, but it is not specific to iron deficiency anemia.
- Bilirubinemia is not a diagnostic test for iron deficiency anemia, as it is related to liver function and hemolysis rather than iron stores.