From the Guidelines
Iron deficiency is best diagnosed on blood tests by measuring serum ferritin levels, which is the single most useful marker of iron deficiency anaemia, as recommended by the British Society of Gastroenterology guidelines 1.
Diagnosis of Iron Deficiency
To diagnose iron deficiency, the following blood tests are helpful:
- Serum ferritin levels: a level below 30 ng/mL generally indicates iron deficiency, though some experts use a threshold of 45 ng/mL or even higher in certain populations
- Complete blood count (CBC) to check for anemia (low hemoglobin and small, pale red blood cells)
- Transferrin saturation below 20%
- Elevated total iron-binding capacity (TIBC)
- Low serum iron levels In cases where ferritin results are unclear, such as when inflammation is present, soluble transferrin receptor levels may be measured as they remain unaffected by inflammation 2.
Interpretation of Test Results
It's essential to interpret the test results in the context of the patient's clinical symptoms and risk factors. 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.
Additional Considerations
Fasting before the blood test is recommended for accurate serum iron measurements. Additionally, iron deficiency develops in stages, and abnormal red blood cell indices and anemia appear only in later stages, so normal hemoglobin doesn't rule out iron deficiency 3.
Key Points
- Serum ferritin is the most sensitive and specific test for iron stores
- A combination of blood tests, including CBC, transferrin saturation, TIBC, and serum iron, can help confirm the diagnosis
- Soluble transferrin receptor levels can be measured in cases where ferritin results are unclear
- Interpretation of test results should be done in the context of the patient's clinical symptoms and risk factors.
From the Research
Diagnosing Iron Deficiency on Blood Test
To diagnose iron deficiency on a blood test, several markers can be used, including:
- Ferritin level: This is the most important analysis in the study of iron deficiency 4. However, there is no consensus on the diagnostic cut-off, with some studies suggesting a cut-off of 12-20 μg/L 4, while others propose a higher cut-off of 30 μg/L 4, 5.
- Transferrin saturation (TSAT): This can be used as an alternative or complementary diagnostic test 6, 7. A cut-off of 20% for TSAT has been proposed in some guidelines 7.
- Transferrin receptor in plasma: This increases with iron deficiency without being influenced by inflammation and is therefore a good supplement to ferritin measurement 4.
- CRP level: This should be considered in conjunction with ferritin level, as ferritin increases with inflammation 4.
Interpretation of Biochemical and Haematological Findings
The interpretation of biochemical and haematological findings is crucial in diagnosing iron deficiency. However, there is no standardization or consensus on the interpretation of these findings 4. The use of ferritin as a diagnostic test of iron deficiency and overload is a common clinical practice, but its levels are elevated in inflammation and infection 5.
Cut-off Values for Iron Deficiency and Overload
Different cut-off values have been proposed for iron deficiency and overload, including:
- Ferritin cut-off of 100 μg/L for serum ferritin concentration in most conditions 7.
- Ferritin cut-off of 30 μg/L for detecting iron deficiency in people presenting for medical care 5.
- TSAT cut-off of 20% for diagnosing iron deficiency 7.
- Ferritin concentration of 500 μg/L or higher for iron overload 8, 7.