Anaemia and polycythaemia Flashcards
What is anaemia and what variables does it affect?
Reduction in the amount of haemoglobin in a given volume of blood below what would be expected in comparison to a healthy individual.
This is a reduction in the absolute amount of haemoglobin.
RBC and Hct are also reduced
What are the mechanisms of anaemia?
Pooling of blood in a very large spleen
Fewer RBC production from the bone marrow
Less RBC surviving in circulation
Blood loss
What are the classifications of anaemia on the basis of size?
Microcytic - hypochromic
Normocytic - normochromic
Macrocytic - hyperchromic
What are the causes of microcytic anaemia?
This is failure of haem synthesis due to:
- Iron deficiency
- Anaemia of a chronic disease
- GIT lesion or cancer
Defect in the Globulin chain (thalassaemia)
-Can be in the alpha or the beta chain
What are the causes of macrocytic anaemia?
This is due to failure of DNA synthesis and so there is abnormal haemopoiesis.
RBC are larger than normal.
Vitamin B12 or folic acid deficiency
Liver disease and ethanol toxicity
Drugs interfering with DNA synthesis such as chemo.
Recent blood loss - when you lose blood the bone marrow will start spitting out reticulocytes hence an increased MCV
Haemolytic anaemia
Common in: vegans, vegetarians and pregnancy
What are the mechanisms and causes of normocytic anaemia?
Mechanisms:
Recent blood loss
Failure of production of RBC and pooling of RBC in the spleen.
(The MCV and the MCH will be normal)
Causes:
- Peptic ulcer
- Oesophageal varices
- Trauma
- Hyepersplenism
- Failure of production of RBC(early stages of iron deficiency, renal failure, bone marrow failure or suppression, bone marrow infiltration)
What is the difference between macrocytic and megaloblastic?
Macrocytic means that there is an increased MCV.
In megaloblasts there is a lack of nucleus maturation but the cytoplasm continues to mature. This means that megablasts are very large with nucelo-cytoplasmic dissociation.
I.e. Macrocytic anameia can be due to megaloblatic erythropoieisis.
What are the possible causes of macrocytic anaemia related to RBC and bone marrow ?
Megaloblastic erythropoeisis
Premature release of the RBC from the bone marrow- this means that there are more reticulocytes in the circulation and as these are 20% larger this can lead to an increase in the MCV.
What is haemolytic anaemia?
This is anaemia caused by a reduced survival of RBC in the circulation due to intrinsic or extrinsic abnormalities.
The normal life span is 120 days.
This can be:
- Inherited (cell membrane defect, the enzymes in the RBC or haemoglobin defect)
- Acquired (drugs, chemicals and microorganisms)
It can be:
- Intravascular (acute damage to the RBC)
- Extra-vascular (defective RBC are removed by the spleen)
Explain the relevance of Glucose-6-phosphate deficiency to anaemia:
G6P is an enzyme which is involved in the pentose pathway and generates NADPH and pentose sugar. It is the only source of reduced gluthathione in RBC.
RBC’s role in carrying oxygen puts them at a great risk against oxygen free radicals. The G6P provides a protective role against these radicals so without it the RBC is at risk of haemolytic anaemia when there is oxidative stress.
Gene is carried on the X chromosome so is more in males than females.
Will get irregularly contracted cells - Heinz bodies. (can get more than one unlike Howell Jolly body)
Explain the relevance of a deficiency in pyruvate kinase on anaemia:
Pyruvate kinase is involved in the final stage of glycolysis.
This means that is needed to generate energy and without it there will be a decreased energy.
This is the only source of ATP and as RBC do not have nuclear material they cannot generate ATP and cellular death occurs.
When should you suspect haemolyitic anaemia?
Otheriwise unexplained anaemia that is normochromic and uslaly normocytic or macrocytic.
Evidence of:
- morphologically abnormal RBC
- Increased RBC breakdown
- Increase bone marrow activity
- Jaundice (greater breakdown of cells means that there will be more bilirubin in the system hence yellow sclera)
- Bile pigment gall stones
Explain the mechanisms of hereditary spherocytosis:
This is a type of haemolytic anaemia or chronic compensated haemolysis.
After entering the circulation the RBC lose their cell membrane and become spherocytes.
This means that they are larger and rounder - increased MCHC.
They become less flexible and are removed in the spleen.
The bone marrow tries to compensate by increasing production leading to polychromasia and reticulocytosis –> these cannot pass through the membrane of the spleen so are removed.
What are the treatments for hereditary spherocytosis?
Splenectomy - this is a very risky procedure so is only carried out in extreme situations.
Diet - need to insure secondary folic acid deficiency doesn’t occur.
Or a folic acid tablet can be taken once a day.
What is the cause of acute haemolytic anaemia?
This is when there are antibodies produced against the RBC antigens.
This means that the splenic macrophages will remove the cell membrane and from spherocytes.
The spherocytes are less flexible and so are more likely to be removed by the spleen.
