Introduction
Iron studies are indicated in patients with anaemia, particularly those with microcytic anaemia.
They may also be indicated in microcytosis (without anaemia), general lethargy and tiredness and malnutrition.
Iron studies are particularly useful to distinguish iron-deficiency anaemia from other microcytic anaemias (usually anaemia of chronic disease, or rarely thalassaemia)
In many cases of iron deficiency anaemia, the diagnosis is straightforward, and can be made using a combination of history (blood loss, low iron in the diet, malabsoprtion, lack of risk factors for thalassaemia, lack of medical history indicating a chronic disorder ) and a full blood count (FBC) – which would show a macrocytic anaemia (↓Hb and ↓MCV).
This is fine in simple, straightforward, uncomplicated patients. Unfortunatly (for us as clinicians) in the real world, and particularly in hospital, nothing is straightforward, and many patients may have an underlying chronic disease.
Iron studies are most useful for patients with anaemia and a chronic disorder (most commonly chronic renal failure, but could be chronic infection, inflammation or a malignancy)
In these patients, ↓Hb and ↓MCV can occur either a result of iron deiciency or the anaemia of chronic disease, or thalassaemia and it is important to distinguish the two as the treatments differ.
Interpretation
So, its pretty straightforward, but something you’ll need to learn, so heres important bit:
| Iron def. anaemia | Anaemia of chronic disease | β-thalassaemia | Haemochromatosis | |
| Serum Iron | ↓ | ↓ | ↑ or ↔ | ↑ |
| TIBC – (Transferrin) | ↑ | ↓ | ↔ | ↓ |
| Serum Ferritin | ↓ | ↑ or ↔ | ↑ or ↔ | ↑↑ |
| MCV | ↓ | ↑ or ↔ | ↑ or ↔ | ↑↑ |
Key Points
- Both iron deficiency and anaemia of chronic disease with have low iron
- Iron deficiency anaemia will have high TIBC – this is because is iron deficiency anaemia, as iron stores are depleted, the body tries to compensate by increasing the serum’s ability to carry iron. In Anaemia of chronic disease, the low serum iron is a result of low TIBC.
- Iron deficiency will have low ferritin – ferritin is a measure of iron stores. In iron deficiency anaemia these are depleted. In anaemia of chronic disease, there is a not a problem with iron stores, but instead with iron utilisation / transfer, so ferritin levels will be normal or high.
*WARNING*
Iron levels are not a always a reliable indicator – iron is also an acute phase biochemical marker – and will rise with inflammation – like CRP or ESR.
- Take iron levels with a pinch of salt. Loads of things can alter serum iron levels:
- False normal – if a patient is taking supplements
- False low – acute or chronic inflammation, ongoing infection, post-operatively, malignancy, hypoalbuminaemia
References
- Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
- Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
- Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
