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Blood pathology


Defect in synthesis of either the alpha or beta globin chains in haemoglobin.

Beta Thalassaemia

  • Caused by gene mutations
  • If heterozygous, usually asymptomatic.
  • In homozygous, large amounts of HB A2 and Hb F. Not as good an normal Hb A, but can cope, though in severe cases regular 6 week transfusions will be required – can lead to iron overload.

Alpha Thalassaemia

  • Caused by gene deletions
  • If all four are deleted you get Hb Barts which isn't compatible with life. Children are stillborn or die shortly after birth.
  • If three are deleted some Hb A is present, and usually transfusion are not necessary.
  • If 2 or less are deleted. Often not noticeable.


For more, see the pages on anaemia and causes of anaemia.

Sickle cell anaemia

  • A base mutation
  • No Hb A, just Hb S and Hb F in homozygous
  • Carriers (heterozygous) will have sickle cell trait, with some signs of illness.
  • Often presents with acute pain in hands and feet, due to vaso-occlusion of small vessels.
  • Pigment stones can occur due to rapid haemolysis.
  • Anaemia is present since sickle cells are broken down quickly. This can present with jaundice, due to increased levels of bilirubin getting released.

Aplastic anaemia

  • Non functioning bone marrow
  • Dangerous but uncommon.
  • Can be caused by some chemicals and drugs (especially anticancer ones), radiation, infections and pregnancy (where it has 90% mortality).
  • Leads to pancytopenia – a reduced red, white and platelet cell count.

Haemolytic anaemia

  • Excessive rate of erythrocyte breakdown.
  • Causes jaundice (due to excess bilirubin)
  • Associated with blood transfusion mismatch.
  • Haemolytic anaemia of the newborn (when the mother is Rhesus – and the baby Rhesus + sometimes there can be a sever complication)
  • Increased young cells, reticulocytes due to high turnover.

Megaloblastic anaemia

  • Maturation of the normoblast needs vitamin B12 and folate.
  • Without this it leads to formation of abnormally large megaloblasts which become macrocytes.
  • Number of red cells is greatly reduced and the rate of destruction increased.
  • Folate defiency is usually related to poor diet, B12 is malabsorbtion

Pernicious Anaemia

  • B12 deficiency, with defective absortion in the ileum.
  • Caused by diet, or autoimmune disease where antibodies attack gastric parietal cells, so intrinsic factor can't be made.
  • Treatment by B12 intramuscular injections till sorted then every 3 months for life.


  • A skin rash due to capillaries bleeding into the skin.
  • Easy bruising
  • Can be due to capillary defects, platelet deficiency or malabsorbtion (eg. Vitamin K)

Non Muco-Cutaneous

(Haemophilias, with bleeding into joints and muscles)

Haemophilia A

  • Level of factor VIII is reduced, but vWF is normal.
  • Sex linked on the X chromosome.
  • Rare 1 in 10000

Haemophilia B

  • Same as A, except factor IX is reduced.
  • Very rare, 1 in 50000


vWD and platelet disorders.

Von Willebrand's disease (vWD)

  • Autosomnal dominant.
  • There is defective platelet function as well as factor VIII:C deficiency.
  • Leads to longer extrinsic pathway.

Platelet disorders

  • Pretty rare.
  • Drug effect more common.

Vitamin K deficiency

  • Needed for factors II, VII, IX and C and proteins C and S.
  • It is a fat soluble vitamin needing bile for absorption – so in obstructive jaundice you get malabsorbtion.
  • PT is prolonged.
  • Warfarin is a Vitamin K inhibitor
  • Neonates tend to have deficiency due to lack of gut bacteria and low conc of K in milk.


(Disseminated Intravascular Coagulation)

  • Widespread generation of fibrin within the blood.
  • Caused by diffuse endothelial damage, generalised platelet aggregation.
  • Causes 1 sepsis, 2 obstetric, 3 malignancy – assume sepsis and treat for this.
  • Also, burns, liver disease, trauma, malignant disease, septicaemia, haemolytic transfusion errors.