Haemolytic Anaemia Flashcards
What is haemolytic anaemia?
The premature destruction of red cells, caused by:
- Something outside the red cell attacking it – extrinsic (acquired)
- Defects within the red cell cause its destruction – intrinsic (inherited)
As a form of compensation the normal adult marrow can produce red cells at 6-8 times the normal rate. Therefore may not see haemolytic anaemia until lifespan of red cells <30 days
Cells must be entirely flexible. All of their energy comes from anaerobic respiration (generates two ATP) - this maintains the membrane structure and keeps cells flexible.
The capillaries and splenic architecture have a much smaller width than the RBCs (2.5 um width), hence the cells must deform to fit.
So if there is something wrong with the membrane they won’t deform correctly to fit though.
Also, the spleen is generally hypoxic, which causes additional metabolic stress on the cell.
Macrophages in the spleen recognise this defect and destroy the trapped RBCs through hereditary spereocytosis - red cell membrane defect.
What can cause intrinsic/hereditary haemolytic anaemia?
Membrane:
Hereditary spherocytosis, hereditary elliptocytosis
Haemoglobin:
Also the majority of RBC mass is haemoglobin, so if there is a defect in the folding of this protein then the membrane will be defected, for example genetic abnormalities (Hb S, Hb C - unstable)
Metabolism:
Intrinsic HA can also result from issues with metabolism, e.g. G6PD deficiencies (stop the proteins becoming oxidised), or pyruvate kinase deficiencies.
What are the causes of acquired haemolytic anaemia?
Immune:
- Autoimmune disorders (warm and cold antibodies)
- Alloimmune (Haemolytic transfusion reactions, HDTN, SC transplants)
Drug associated:
- infections (malaria, clostridia)
- chemical and physical agents; drugs such as penicillin, industrial/
domestic substances, burns
Secondary:
- liver disease
- Renal disease
What is acquired/extrinsic haemolytic anaemia?
RBCs tends to be broken down by extra vascular haemolysis - spleen, which attack at site of break down.
There is nothing wrong with the red blood cell itself
It is destroyed due to some pathological process ⁻ Drugs ⁻ Toxin ⁻ Autoantibody ⁻ Infection
Normal red blood cells have a mean lifespan of 120 days. Majority are removed from the circulation by the phagocytic activities of macrophages in the liver, spleen and lymph nodes - Extravascular
Red cells are phagocytosed by the macrophage (could be normal) and broken down to globulin and haem. This increased breakdown in extavascular haemolysis leads to increased bilirubin and thus urobiligen in the urine (measured in the lab).
Also, unlike IDA, TIBC will also become saturated, because transferrin will be transferring all this broken down haem to saturate it and ferratin.
Splengomegally can occur due to overwork of RBCs = swollen spleen.
How are RBCs broken down intravascularly during acquired haemolytic anaemia?
RBCs are destroyed within the vascular compartment - this plays only a small part of normal red cell destruction.
Haemoglobin (Hb) is released, but in its free form can cause free radical toxicity. Hence it is rapidly bound by the serum protein haptoglobin. The haptoglobin-Hb complex is recognised by monocytes/macrophages and degraded.
Formation of large amounts of haptoglobin-Hb complexes leads to rapid haptoglobin depletion. In order to produce more, signals in the cell must go through transatin cascade in the cell, this takes time.
As a result, haem in Fe3+ state binds to albumin to become methaemalbumin.
Excess free Hb goes to kidney and excreted in urine (haemoglobinuria) - haemosiderinuria also occurs due to iron accumulating in renal tubules.
This is how intrinsic and extrinsic HA are differentiated.
How is acquired haemolytic anaemia diagnosed?
Evidence of red cell damage on peripheral blood film:
- spherocytes
- elliptocytes
- schistocytes,
- aniso/poikilocytosis
Evidence of increased RBC production: ⁻ high reticulocyte count ⁻ Erythroid hyperplasia in bone marrow - Normal myeloid:erythroid ratio of 2:1 reduced or reversed = Nucleated RBCs
Evidence of haemolysis: ⁻ Bilirubin (direct & indirect)↑ ⁻ Stercobilinogen↑ ⁻ Serum haptoglobins↓ ⁻ LDH ↑ - urobiligen ↑
Evidence of membrane abnormalities:
- Osmotic fragility - if membrane abnormality eg spherocytosis
Evidence of antibody involvement:
- Direct Antiglobulin Test – Positive (extrinsic)
(Decreased serum haptoglobins)
(Saturated ferritin and transferrin)
Splengomegally
What is alloimmune haemolysis in acquired HA?
Foreign red cells have been introduced
- Pregnancy or blood transfusion
- Haemolytic disease of the newborn
- Antibody produced by mother after exposure to foetal blood crossing
the placenta
- Antibody crosses back over placenta and attaches to foetal cells in
utero this results in haemolytic anaemia
- positive DAT - Blood group incompatible transfusion
- Patient will produce antibodies to foreign antigens on RBC’s
- Antibodies will then attach to the antigens on the red cells and
cause haemagglutination and subsequent lysis
- Positive DAT
What is hereditary spherocytosis?
An intrinsic/inherited haemolytic anaemia
Most common hereditary haemolytic anaemia in Northern Europeans.
Most affected individuals have mild or only moderate haemolysis. Tends to be very heterogenous in presentation, some people can be very mild, while some can be bad.
Deficiency or dysfunction of one of the constituents of the red cell cytoskeleton:
- Ankyrin
- alpha/beta spectrin
- band 3 protein
- protein 4.2
- can be horizontal or vertical; transmembrane proteins are vertical interactions, others are horizontal. Any mutation in any protein lead to cell membrane defect in RBCs.
How is hereditary spherocytosis diagnosed?
Increased red blood cell destruction:
- ↑indirect bilirubin concentration
- ↑ excretion of urobilinogens
- ↑LDH
Anaemia – severity tends to be similar in members of the same family
Reticulocytes - 5-20%
Blood film shows microspheres
- Spherocytes are selectively trapped in the spleen and destroyed
- Spherocytes on blood film (must constitute > 1–2%)
Test for osmotic fragility of RBC
Important to rule out other causes of HA – the direct antiglobulin test (DAT) is normal excluding autoimmune HA
What are haemoglobinopathies?
Haemoglobinopathies are among the most common inherited diseases around the world
They encompass all genetic diseases of haemoglobin = intrinsic haemolytic anaemia
They fall into two main groups:
- Thalassaemia syndromes – (α- and β-thalassaemia)
- Hb synthesis disorders = not producing enough Hb
- Quantitative defects
- Structural haemoglobin variants – (HbS, HbE and HbC)
- producing correct amount of structurally abnormal haemoglobins
- Qualitative defects
What is sickle cell anaemia?
QUALITATIVE HAEMOGLOBINOPATHY
Structural variant of normal adult haemoglobin - HbS
- Results from a single amino acid substitution at position 6 of the
beta globin molecule (β 6Glu→Val). Valine is a non- polar AA that
causes RBCs to be sticky creating long fibres
- HbS is the most common pathological haemoglobin variant
worldwide
When HbS is inherited from both parents, the homozygous child suffers from sickle cell anaemia
When HbS is inherited from only one parent, the heterozygous child a carrier usually an asymptomatic carrier
- normal RBCs with Hb-A (globular structure) is flexible to allow it to travel from high O2 to low O2 RBCs down narrow capillaries.
- Hb-S in SCA (long fibrous structure), undergo repeated suckling events which causes them to become stiff and inflexible, hence they cannot fit easily through the micro-vasculature.
- the Hb-S RBCs caught behind the stiff, inflexible cells lose their oxygen to the surrounding hypoxic tissue, causing them to sickle. This can cause a blockade, leading to necrosis - tends to be in extremities due to the low local pressure.
- This only happens in low oxygen (hypoxic) conditions such of the spleen - can destroy splenic architecture.
What are the clinical features of SCA?
- Painful vaso-occulsive crises (blockages in capillaries)
- Visceral sequestration crisis (blockages in extremities)
- Aplastic crisis (bone marrow can’t produce anymore so stops
producing RBCs) - Haemolytic crisis
Sickle cells on blood film
Can get a broad range of Hb concentrations 60-90 g/L
Haemoglobin profile
⁻ >80% HbS
⁻ 5-15% HbF
⁻ Normal HbA2
- Usually treat with blood transfusion or hydrouria (reductive
therapy - promotes the formation of foetal Hb)
What is thalassaemia?
Mutations in one or more of the globin genes resulting in a decrease or absence of the corresponding globin chain
Approx. 1-5% of the world’s population are thought to be carriers of beta-thalassaemia
Normal adult Hb is HbA (α2 β2k) chains produced at 1:1 ratio
In alpha or beta thalassaemia synthesis of one of these chains is decreased or absent
- If α-chain is affected you have an excess of β-chains
- If β -chain is affected you have an excess of α -chains
What are the clinical findings in thalassaemia?
The severity of the anaemia depends on the gene mutation and number of genes affected:
Decreased Hb production - ↓RBC count, ↓Hb
Ineffective erythropoiesis - microcytic hypochromic RBCs,
anisocytosis/poikilocytosis, ↑retics,
target cells, nucleated RBCs
Abnormal Hb electrophoresis - HbH, Hb Barts
Splenomegaly
Haemolysis - ↓haptoglobins, ↑Bilirubin, ↑ LDH
Skeletal abnormalities and fractures due to expansion of BM - BM erythroid hyperplasia
Increased iron absorption
What is alpha thalassaemia?
Chromosome 16 carries 2 alpha globin genes
- Therefore have 4 copies of alpha-globin overall
Most mutations in alpha thalassaemia are deletions leading to a reduced or absent alpha chain
In a one gene mutation: -/α/α/α/, the output is 75% of normal and generally clinically silent
Mutations in two genes: -/-/α/α/ or -/α/-/α/, this is described as alpha-thalassaemia minor or an alpha-thalassaemia carrier.
- Alpha globin production is 50% of normal
Complete loss of all four alpha genes: (-/-/-/-), results in haemoglobin Bart’s (also called hydrops fetalis syndrome)
- Unable to produce any alpha globin chains to make HbF OR HbA.
- Incompatible with life
- Foetal blood contains mainly Hb Bart (gamma 4) and small amounts
of haemoglobins Portland 1 and 2 (zeta2 gamma2 and zeta2 beta2).
- The clinical picture is very severe anaemia (Hb 30–80 g/L), marked
hepatosplenomegaly, hydrops fetalis, and cardiac failure
