56. Haemolytic anaemias

Conditions that cause destruction of RBCs (and therefore decrease their lifespan) are called haemolytic anaemias. Two types exist:

Corpuscular haemolytic anaemias have some problems with the RBCs themselves that causes them to have decreased lifetime. Common problems include problems with the membrane, enzymes or haemoglobin.

Extracorpuscular haemolytic anaemias include healthy RBCs, however external factors cause them to be destroyed, like mechanical trauma, toxins or autoimmune diseases.

Corpuscular haemolytic anaemia

Membrane abnormalities of RBCs:

• Hereditary spherocytosis is a genetic disease where the RBCs are spherical instead of biconcave discs.
• Liver damage causes RBCs to take a special form called spur cells
• Paroxysmal nocturnal haemoglobinuria is an acquired disease where RBCs are destroyed by the complement system, especially during the night.

Enzyme deficiencies of RBCs:

• Glucose 6-phosphate dehydrogenase deficiency (G6PD) is a common genetic disease where the RBCs can’t produce enough NADPH due to problems with the pentose phosphate pathway. Low NADPH levels causes low GSH levels, which is the most important anti-oxidant. This makes the RBCs very susceptible to oxidative stress, like during acidosis, infections or uraemia.
• Pyruvate kinase deficiency is another disease where the glycolysis is deficient

Abnormal haemoglobin:

• Sickle cell anaemia is a genetic disease where a switch from glutamate to valine on the haemoglobin β-chain causes deoxygenated haemoglobin to precipitate inside the RBC. RBCs in the venous circulation will therefore take on a sickle-cell shape. These sickle-cells are haemolysed in the spleen. They can block capillaries, leading to tissue damage.
• Thalassaemia A is a genetic disease where there is a deficiency of the α-chain. Homozygotes are said to have thalassaemia A major and heterozygotes have thalassaemia A minor.
• Thalassaemia B is a genetic disease where there is deficiency of the β-chain. Homozygotes have thalassaemia B major while heterozygotes have thalassaemia B minor

Red blood cells in thalassemia major (both A and B types) are hypochromic and microcytic with anisocytosis. To compensate for the very inefficient RBCs will the body start to have haematopoiesis other places than the bone marrow, called extramedullary haematopoiesis. This can form masses in the posterior mediastinum, and the hyperplastic bone marrow causes skeletal changes.

Here are some other abnormal haemoglobins, classified by whether they cause left shift (decreased oxygenation) or right shift (increased oxygenation) of the haemoglobin-oxygenation curve.

Left shift	Right shift
Hb Rainier	Hb Kansas
Hb Barts	Hb Seattle
Hb H (Thalassaemia A major)	Hb S (sickle-cell anaemia)

Extracorpuscular haemolytic anaemia

The most frequent causes are:

• Mechanical trauma
  • Artificial valves
  • Valvular stenosis
  • March haemolysis (marching or running can cause RBCs to haemolyse! Google it)
• Immune-mediated haemolysis
  • Incompatible blood transfusion
  • Erythroblastosis foetalis
  • Autoimmune haemolytic anaemia
  • SLE
  • Hypersensitivity type II
    • Drugs can bind to RBCs and be recognized by the immune system as foreign
    • Penicillin
    • Methyldopa
• Splenomegaly
• Uraemia
• Malaria

Consequences

Apart from the general consequences of anaemias can we see the following consequences:

• Indirect hyperbilirubinaemia
• Haemoglobinuria
• Toxic acute tubular nephropathy – because of the elevated serum haemoglobin
• High ratio of reticulocytes to RBCs in the blood