Flashcards in Haemolysis Deck (71)
What is haemolysis?
An increase in breakdown of RBCs
What happens if the bone marrow is unable to compensate for the increased red cell turnover in haemolysis?
What can haemolysis be broadly grouped into?
- Inherited causes
- Acquired causes
What are inherited causes of haemolysis usually due to?
Intrinsic red blood cell abnormalities
What are acquired causes of haemolysis usually due to?
Give an example of an acquired mechanism of haemolysis?
Antibody-mediated destruction in immune haemolytic anaemias
What cause of haemolytic anaemias account for the majority of cases in children?
Intrinsic red cell abnormalities
What do blood tests show in haemolytic anaemia?
- Reduced Hb
- Raised reticulocytes
- Raised unconjugated bilirubin
- Raised LDH
- Low haptoglobin
Why is LDH raised in haemolytic anaemia?
The LDH enzyme is present at high levels in RBCs, and so during haemolysis, lysis of RBCs causes large amounts of LDH to be released into the circulation
Where in the body does haemolysis occur?
Can occur in the circulation (intravascular) or in various organs, such as the spleen (extravascular)
What does intravascular haemolysis lead to?
Depletion of haptoglobin, increased LDH, and large numbers of fragmented red blood cells, called schistocytes.
Why does intravascular haemolysis lead to a depletion of haptoglobin?
Haptoglobin binds to free haemoglobin in the plasma to form a haptoglobin-haemoglobin complex, which is then removed from the circulation by the reticuloendothelial system (mostly in the spleen)
What happens after haptoglobin is depleted?
Free haemoglobin is filtered by the kidney
What happens to filtration of free haemoglobin by the kidney in severe cases of intravascular haemolysis?
The reabsorption is overwhelmed
Where in the body is LDH present?
It is present in many tissues, but has high concentrations within RBCs
Where does extravascular haemolysis take place?
Usually in spleen or liver, but can also occur in lung
What is the mechanism of extravascular haemolysis?
Spleen or liver macrophage Fc receptors bind immunoglobulin attached to red blood cells and then either ingest small portions of the cell membrane, creating spherocytes, or phagocytose the whole cells
What happens to the products of extravascular haemolysis?
- Amino acids from globing chains are recycled
- Iron is removed from haem and reused
- Haem is degraded into unconjugated bilirubin
What provides useful clues into the diagnosis and aetiology of haemolysis?
The blood film
What might the blood film show in haemolysis?
- Sickle-shaped cells
- Fragmented red cells
What is polychromasia?
An increase in immature red blood cells (reticulocytes)
How do reticulocytes appear on most blood film stains?
What is the significance of sickle-shaped cells in blood films?
Diagnostic of sickle cell disorders
When might spherocytes be seen on blood film?
- Hereditary spherocytosis
- Immune haemolytic anaemias
What are the types of fragmented red blood cells?
- Degmacytes, or 'bite' cells
What are bite cells typical of?
Oxidative haemolysis, e.g. G6PD deficiency
When are schistocytes seen?
In intravascular haemolysis, e.g. haemolytic uraemic syndrome
What does the direct antiglobulin test (DAT) detect?
The presence of antibodies coating RBCs
What is DAT essential for?
Diagnosis, or exclusion, of immune-mediated haemolytic anaemia