Expansion
Driven by erythropoietin, requiring iron, B12 and folate
Expansion
- Site: bone marrow. In adults, the axial skeleton, proximal femur and humerus; in children, all bones; in the fetus, yolk sac then liver and spleen
- Stimulus: erythropoietin from the kidney in response to hypoxia
- Requirements: iron, vitamin B12, folate, plus protein and trace elements
- Time: about 7 days from stem cell to reticulocyte release
- Lifespan: 120 days, after which cells are removed by splenic macrophages
Reticulocytes are the key clinical index:
- High in haemolysis or acute blood loss: the marrow is responding
- Low or normal in anaemia of marrow failure, iron deficiency, B12 or folate deficiency, or renal disease
Classifying anaemia by mean cell volume narrows the cause quickly: microcytic for iron deficiency and thalassaemia, macrocytic for B12 and folate deficiency, alcohol, hypothyroidism and myelodysplasia, and normocytic for acute blood loss, haemolysis, chronic disease and renal failure.