Anaemia
Anaemia is defined as the reduction in circulating red blood cell-mass below normal levels. It reduces the oxygen-carrying capacity of the blood, leading to tissue hypoxia. It is diagnosed by haemoglobin concentration. The WHO defines anaemia as a haemoglobin concentration < 13 g/dL for men and < 12 g/dL for women, but the normal ranges vary a bit from laboratory to laboratory.
People with chronic anaemia develop compensatory mechanisms, which is why they can function with lower Hb.
Classification of anaemias according to morphology
Anaemias can be classified according to the morphology of the RBCs or according to the etiology.
| Microcytic anaemia | Normocytic anaemia | Macrocytic anaemia | |
|---|---|---|---|
| MCV (fL) | < 80 | 80 – 100 | > 100 |
| Pathomechanism | Insufficient haemoglobin production | Increased RBC loss and/or decreased erythropoiesis | Insufficient RBC production and/or maturation, possibly due to defective DNA synthesis or DNA repair |
| Possible causes | Iron deficiency anaemia | Haemolytic anaemias: | Vitamin B12 deficiency |
| Anaemia of chronic disease (late phase) | Sickle cell anaemia | Folate deficiency | |
| Thalassaemia | G6PD deficiency | Certain drugs (phenytoin, sulfa drugs) | |
| Lead poisoning | Paroxysmal nocturnal haemoglobinuria | Fanconi anaemia | |
| Chronic blood loss | Hereditary spherocytosis | Liver disease | |
| Autoimmune haemolytic anaemia | Alcohol abuse | ||
| Microangiopathic haemolytic anaemia (TTP/HUS) | |||
| Macroangiopathic haemolytic anaemia | |||
| Non-haemolytic anaemias: | |||
| Acute blood loss | |||
| Aplastic anaemia | |||
| Anaemia of chronic disease (early phase) |
Classification of anaemia according to reticulocytes
In response to anaemia, a healthy bone marrow will increase production of RBCs. This is evidenced on labs as an elevated reticulocyte count. If reticulocytes are not elevated or are decreased, it points to a primary problem with the bone marrow causing the anaemia.
- Increased reticulocytes – bone marrow works hard
- Bleeding
- Haemolysis
- Decreased reticulocytes – bone marrow doesn’t work
- Aplastic anaemia
- Leukaemia
- Myelodysplasia
- Myelofibrosis
- Chronic kidney disease (EPO deficiency)
General clinical features of anaemia
- Fatigue
- Pallor – especially of lips and conjunctiva
- Weakness
- Exercise intolerance
- Palpitations
- Tachycardia
For more specific features, see the article of the specific form of anaemia.