Post-haemorrhagic anaemia
Anaemia from blood loss is divided into acute and chronic forms, which differ in the speed of loss, the blood picture and the organ changes.
Anemia: definition, etiology and classification
Definition
Anemia is a reduction in the haemoglobin concentration, the red cell mass (haematocrit) and therefore the oxygen-carrying capacity of the blood. By the usual WHO reference thresholds, haemoglobin is below about 13 g/dL in men and 12 g/dL in non-pregnant women. Anemia is a sign of an underlying disease, not a diagnosis in itself.
Etiology: pathogenetic classification
- Blood loss - acute (trauma, ruptured vessels) or chronic (gastrointestinal, menstrual loss).
- Increased destruction of red cells (haemolytic anemias), with raised reticulocytes and signs of haemolysis.
- Intracorpuscular (defect inside the red cell): hereditary spherocytosis, sickle cell disease, thalassaemia, G6PD deficiency.
- Extracorpuscular (cause outside the cell): autoimmune haemolysis, mechanical damage (e.g. prosthetic valves), infections such as malaria, toxins.
- Impaired red cell production:
- Iron deficiency anemia.
- Vitamin B12 deficiency (e.g. pernicious anemia) and folate deficiency (megaloblastic anemias).
- Aplastic anemia (marrow failure).
- Marrow infiltration (leukaemia, metastatic tumour, fibrosis).
- Anemia of chronic disease (inflammation, chronic infection, cancer) and chronic renal failure (lack of erythropoietin).
Morphological classification
Anemias are also grouped by red cell size (mean corpuscular volume, MCV) and haemoglobin content (MCH, MCHC) on the blood film.
The classification links to this topic: acute blood loss gives a normocytic normochromic anemia, while chronic blood loss ends as a microcytic hypochromic iron deficiency anemia.