From the Guidelines
The primary diagnostic blood tests for iron deficiency anemia include hemoglobin, serum iron, total iron-binding capacity (TIBC), and ferritin, with serum ferritin being the single most useful marker of iron deficiency anemia. When diagnosing iron deficiency anemia, the following tests are typically ordered together:
- Hemoglobin and hematocrit levels
- Red blood cell count and indices (MCV, MCH, MCHC)
- Serum iron
- Total iron-binding capacity (TIBC)
- Ferritin According to the most recent guidelines, a serum ferritin level of <30 ng/mL is an appropriate criterion for the diagnosis of iron deficiency anemia in patients without clinical, endoscopic, or biochemical evidence of active disease 1. In patients with inflammation, a serum ferritin level up to 100 mg/L may still be consistent with iron deficiency, and a combination of true iron deficiency and anemia of chronic disease is likely if the serum ferritin level is between 30 and 100 mg/L 1. These tests are effective because they measure both the amount of iron in the blood and the body's iron stores, with ferritin being an excellent indicator of iron stores and often the first marker to decrease in iron deficiency. It is also important to note that a good response to iron therapy, defined as a hemoglobin rise of ≥10 g/L within a 2-week timeframe, is highly suggestive of absolute iron deficiency, even if the results of iron studies are equivocal 1. If iron deficiency anemia is confirmed, further testing may be needed to determine the underlying cause, such as blood loss or malabsorption.
From the Research
Diagnostic Blood Tests for Iron Deficiency Anemia
The following blood tests are used to diagnose iron deficiency anemia:
- Serum ferritin: measures the amount of iron stored in the body 2, 3, 4, 5, 6
- Serum transferrin receptor: measures the amount of transferrin receptor in the blood, which increases with iron deficiency 2, 3, 5, 6
- Transferrin/log(ferritin) ratio: a new parameter that can help diagnose iron deficiency anemia when ferritin levels are inconclusive 2
- Reticulocyte hemoglobin content: measures the amount of hemoglobin in reticulocytes, which decreases with iron deficiency 4, 6
- Mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH): measure the size and hemoglobin content of red blood cells, which can be low in iron deficiency anemia 4, 5
- Serum iron, transferrin saturation, and total iron-binding capacity: measure the amount of iron in the blood and the capacity of transferrin to bind iron, but are not as sensitive or specific as serum ferritin 3, 5, 6
- Soluble transferrin receptor (sTfR)/ferritin index: a combination of markers that can help distinguish iron deficiency from inflammatory anemia 4, 6
- Hepcidin measurements: a new marker that can help diagnose iron deficiency and identify individuals in need of iron supplementation 4
Interpretation of Test Results
The interpretation of test results varies depending on the laboratory and the individual's clinical condition. Generally:
- Serum ferritin levels <20 μg/L are highly specific for iron deficiency anemia, while levels >100 μg/L usually exclude iron deficiency anemia 2
- Serum ferritin levels between 20 and 100 μg/L are often inconclusive and may require additional testing 2
- A transferrin/log(ferritin) ratio of >1.70 indicates iron deficiency anemia in patients with inconclusive ferritin levels 2
- The sTfR/ferritin index can help distinguish iron deficiency from inflammatory anemia 4, 6