Tests for the diagnosis of IDA

Initial tests

IDA may be effectively diagnosed by a full blood examination and serum ferritin level in most cases. Serum iron levels should not be used to diagnose iron deficiency.

The following table provides details as to how a full blood examination and serum ferritin can assist in the diagnosis of IDA:

Application
Can suggest iron deficiency.
Hb g/L value is required to assess severity of anaemia.
Notes

Iron deficiency can occur without anaemia.
Ferritin is required to confirm diagnosis.
Red cell indices such as low MCV and MCH may suggest iron deficiency but can be normal.
A constellation of the following findings on full blood count is highly suggestive of iron deficiency anaemia:

  • anaemia
  • microcytosis
  • hypochromia
Application
Diagnostic test of choice.
Serum ferritin levels and iron status in adults:
  • <15 μg/L is diagnostic of iron deficiency
  • 15–30 μg/L is highly suggestive of iron deficiency
  • >15 μg/L but <100 μg/L possible iron deficiency
  • >100 μg/L iron deficiency unlikely (but consider functional iron deficiency)*

Lower thresholds have been used in children, from 10–12 μg/L.

 

Notes
Ferritin is also an acute phase protein and is elevated in inflammation, infection, liver disease and malignancy.
This can result in misleading elevated ferritin levels in iron deficient patients with coexisting systemic illness.
Markers such as C-reactive protein may help identify coexisting inflammation.

 

*Functional iron deficiency is when iron cannot be mobilised for erythropoiesis despite adequate stores. It is most commonly seen in patients with end-stage kidney disease or inflammatory conditions such as rheumatoid arthritis.

 

Additional tests

Additional tests may be considered when the clinical features and haematology profile are suggestive of iron deficiency, but ferritin is normal. Consider consulting with a pathologist or haematologist before ordering these additional tests.

The following table summarises additional tests which may be of assistance in diagnosis of iron deficiency:

Application
High iron binding capacity and low transferrin saturation are suggestive of iron deficiency (even in the presence of a normal ferritin).
Notes

Serum iron is often reported but only reflects recent intake and is not useful in the diagnosis of iron deficiency.
These tests are recommended when serum ferritin is reported as normal or high and:

  • iron deficiency is suspected clinically, or
  • patient has kidney failure, or
  • chronic infection, inflammation or malignancy is present
Application
Elevated in tissue iron deficiency
Notes
Not sensitive to inflammation.
sTfR/log ferritin ratio is highly correlated with body iron stores.
sTfR estimation is limited by variability in interassay cut-offs, availability and slow turnaround in some laboratories.
sTfR is not routinely available.
Application
Investigation of IDA in complex cases.
Application
May be both diagnostic and therapeutic in patients with probable iron deficiency anaemia.

 

Notes
Unreliable in iron malabsorption or ongoing blood loss.
Reliant on compliance.
Increase in haemoglobin of 10–20 g/L in 2–4 weeks is diagnostic of iron deficiency.
 
References
  1. British Columbia Medical Association. Iron Deficiency – Investigation and Management, June 2010. Available from:http://www.bcguidelines.ca.
  2. Gastroenterological Society of AustraliaClinical update: Iron deficiency, First Edition. SydneyAustralia, Digestive Health Foundation, 2008. Available from: http://www.gesa.org.au.
  3. Pasricha SR, Flecknoe-Brown SC, Allen KJ, Gibson PR, McMahon LP, Olynyk JK, et al. Diagnosis and management of iron deficiency anaemia: a clinical update. MJA 2010;193:525–532. Available from: http://www.mja.com.au.

 

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