Overview
The intensity of the colour of red blood cells is representative of the red blood cell haemoglobin concentration.
Hypochromia
Hypochromia refers to a reduction in the intensity of red blood cell colour.
Signs of Hypochromia
- An increase in central pallor >1/3 of the cell on blood film
- Reduced red cell haemoglobin (MCH / MCHC)
Causes of Hypochromia
Microcytic
- Iron deficiency anaemia
- Anaemia of chronic disease (infection / inflammation / malignancy)
- Thalassaemia
- Congenital sideroblastic anaemia
- Lead poisoning
- Hyperthyroidism
Macrocytic
- Copper deficiency
Hyperchromia
Hyperchromia refers to an increase in the intensity of red blood cell colour. Hyperchromic cells may be spherocytes, microspherocytes or macrocytes.
Signs of Hyperchromia
- Reduction in central pallor on blood film
- Increased red cell haemoglobin (MCH / MCHC)
Causes of Hyperchromia
- Spherocytosis - hereditary spherocytosis, immune haemolysis, Clostridium
- Microspherocytosis - microangiopathic haemolytic anaemia, severe burns
- Macrocytosis - B12/folate deficiency chronic liver disease, alcohol abuse, hypothyroidism, post splenectomy, aplastic anaemia, myelodysplastic syndrome
Polychromasia
Polychromasia refers to macrocytic (large) red blood cells with a bluish tinge, due to residual RNA. These cells are likely reticulocytes, which are immature non-nucleated red cells which have only just extruded their nuclei.
This finding may occur in the context of haemolysis, though may also be seen during recovery following haemorrhage or bone marrow suppression (such as following cytotoxic chemotherapy).
Causes of Polychromasia
- Haemolytic anaemia
- Haemorrhage (acute or chronic)
- Recovery post bone marrow suppression
- Late pregnancy
- High altitude
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