Haemolysis

• Haemolysis = premature red cell destruction
• Red cells particular susceptible to damage due to =

  Need to have bioconcave shape

  Limited metabolic reserve + rely on glucose metabolism

  can’t generate new proteins once in circulation
• Compensated haemolysis =

  Increased red cell destruction compensated by production

  Hb is maintained + patient is not anaemic
• Haemolytic anaemia (decompensated haemolysis)

  Red cell destruction exceeds bone marrow capacity for red cell production

  Hb falls + patient becomes anaemic
• Detecting consequences of haemolysis

  Increased red cell production - erythroid hyperplasia (increased bone marrow red cell production)

  Detection of red cell breakdown products
• Bone marrow response to haemolysis

  Erythroid hyperplasia

  Reticulocytosis
• Blood film - haemolysis

  A) reticulocytes

  B) spherocytes

  
• Reticulocyates are not diagnosis of haemolysis - reflect response to stress.
• Classification of haemolysis

  By site = extravascular vs intravascular

  By primary mechanism = immune mediated vs non-immune
• Extravascular haemolysis =

  Taken up by reticuloendotehlial system - spleen and liver

  Most common

  Most often - immune mediated

  Hyperplasia at site of destruction
• Intravascular haemolysis =

  Red cells destroyed within circulation

  Less common + most are not immune mediated - except ABO MISMATCH

  Caused by direct destruction within circulation

  Due to

  Fibrin strands + heart valves

  Red cell membrane abnormalities

  Red cell enzyme abnormalities - G6PD deficiency

  Haemoglobin abnormalities - sickle cell
• Lab results common to haemolysis =

  anaemia

  increased reticulocytes

  Increased breakdown products

  • LDH
  • unconjugated bilirubin
  • urobilinogen
  • haptoglobin falls
• Intra-vascular haemolysis =

  Free Hb in circulation - urine as haemoglobinuria
• Autoimmune haemolysis

  Warm (IgG) - usually extravascular

  Autoimmune disorders SLE

  Lymphoproliferative disorders

  Drugs

  Infections

  Cold (IgM) - can cause intravascular haemolysis

  Infections EBV + mycoplasma

  Lymphoproliferative disorders
• Allo-immune haemolysis =

  Patient has antibodies that destroy transfused blood

  Antibodies from mother destroy red cells in baby - haemolytic disease of foetus and newborn
• Non-immune haemolysis =

  External to red cell

  Fibrin bands = associated with coagulopathy - DIC

  Mechanical = leaking heart valves + march haemoglobinuria
• Non-immune haemolysis - disorders of red cell

  Membrane

  • hereditary spherocytes
  • PNH - paroxysmal nocturnal haemoglobinuria

  Haemoglobin

  • haemoglobinopathies - sickle cell
  • thalassaemia

  Within cytoplasm

  • enzyme deficiendies - G6PD
  • infections - malaria
• Investigating a patient - haemolysis

  Confirm haemolytic state

  FBC

  Reticulocyte count

  Unconjugated billirubin

  haptoglobins

  LDH

  urinary urobillinogen

  Blood film

  DAT
• DAT = direct antigloblin test