Regenerative vs Non-regenerative AnemiaRegenerative Anemia
Haemorrhage may occur from any site and it may be external (often due to trauma) or internal. Any form of spontaneous haemorrhage with no apparent cause may suggest the presence of an underlying coagulopathy. The most common haemorrhagic presentations are:
- Epistaxis due to disruption or erosion of blood vessels of the nasal cavity by trauma, neoplasia, fungal infection or a foreign body.
- Haematuria which may arise due to haemorrhage from any part of the urinary tract, especially the kidney (due to trauma, neoplasia or idiopathic haematuria) and bladder (due to trauma, cystitis, urolithiasis and neoplasia).
- Melaena, haematochezia or haematemesis due to gastro-intestinal haemorrhage. Meleana refers to the production of black tarry faeces with digested blood whereas haematochezia refers to the production of fresh blood with the faeces. Classically, haematemesis is described as resembling 'coffee grounds' as blood is denatured by a low gastric pH but, as the gastric pH of the dog may vary widely between 2 and 6, vomited blood may also appear as fresh red blood.
- Haemoptysis refers to the production of blood from the respiratory tract. It may occur with severe forms of pneumonia and with pulmonary haemorrhage.
- Haemoabdomen, haemothorax and haemopericardium are all forms of haemorrhagic effusion that occur in body cavities.
Haemolysis may occur in the following processes:
- Immune-mediated disease including Immune Mediated Haemolytic Anaemia and Neonatal Isoerythrolysis.
- Infectious agents including Babesia spp. in dogs and cattle, Mycoplasma haemofelis in cats, Leptospira spp. in various species and Clostridium haemolyticum causing redwater fever in cattle.
- Inherited defects of red blood cells enzymes including pyruvate kinase (which is occur most commonly in West Highland white terriers) and phosphofructokinase (PFK).
- Hypophosphataemia which occurs in post-parturient cattle (causing post-parturient haemoglobinuria), with refeeding syndrome and when animals with diabetes mellitus are stabilised with insulin.
- Exposure to toxins including rape and kale (which contain SMCO radicals) in cattle, onions and garlic in dogs and paracetamol in cats.
- Microangiopathic anaemia which occurs when red blood cells are forced through small meshworks of fibrin as with haemangiosarcomas, disseminated intravascular coagulation (DIC) or bacterial endocarditis.
Haemolysis usually results in a more strongly regenerative response than haemorrhage and can be differentiated by plasma protein concentrations; these will fall with haemorrhage, but not with haemolysis.
The failure to regenerate indicates that there is a failure to produce red blood cells in the bone marrow. Erythrocytes are produced from stem cells in the bone marrow and they then undergo sequential stages of maturation before and after they are released into the circulation.
1. Failure of the bone marrow stem cells to produce erythroid cells
This occurs in the following conditions:
- Pure red cell aplasia
- Aplastic anaemia
- Bone marrow suppression
2. Failure of erythrocyte maturation
This can occur with:
- Iron deficiency
- Vitamin B12/folate deficiency