Microcytosis (Guidelines)
TAM (Treatments and Medicines) NHS Highland
Warning
Audience
- Highland HSCP
The normal MCV depends on age but generally 83 to 101 fL.
Causes
- Iron deficiency
- Thalassaemia and haemoglobinopathy
- Anaemia of chronic disease
- Lead poisoning (rare)
- Inherited sideroblastic anaemia (rare)
History and examination
Look for signs of anaemia. Ask about diet, weight loss and potential blood loss. Review older blood tests.
This table can help differentiate between iron deficiency and thalassaemia (trait).
|
Factor |
Iron deficiency |
Thalassaemia (trait) |
|
Haemoglobin |
Low or normal |
Low or normal |
|
MCV/MCH |
Low but can be normal |
Low – often lower than would expect from haemoglobin concentration |
|
RBC |
Low or normal |
High |
|
RDW |
Elevated |
Normal |
|
Previous FBC |
May be normal |
Persistently low MCV/MCH |
|
Family FBC |
May be normal |
If inherited may have similar abnormalities |
|
Blood film |
May be normal or may show hypochromia and pencil cells. |
Depends on type. |
|
Ethnicity |
Any |
More common in certain ethnic groups |
Suggested Investigations
- Ferritin
- If iron deficiency suspected but ferritin normal then check inflammatory markers (e.g. CRP) as inflammation may elevate ferritin into the normal range.
- Haemoglobinopathy screen if suspected thalassaemia or haemoglobinopathy. Please note that alpha thalassaemia trait is the most common disorder and will not be picked up by a haemoglobinopathy screen. Alpha thalassaemia trait is a benign, asymptomatic disorder. The only two considerations are that firstly the MCV cannot (easily) be used to infer the cause of anaemia as it will always be low and secondly, depending on the level of MCH and ethnicity, partner testing may be required when family planning as per National Screening Programme.
- If lead poisoning is suspected please check Zincprotoporphoryn, serum lead level and blood film
- In some patients a trial of iron may be a diagnostic and therapeutic manoeuvre
Management
- We do not review patients with iron deficiency in haematology.
- See section on iron deficiency for more
- We do not review patients with thalassaemia trait but happy to be contacted via Clinical Dialogue if concerns or further questions.