Anaemia and polycythaemia Flashcards
Define what is meant by anaemia
Anaemia is a reduction in the amount of haemoglobin in a given volume of blood below what would be expected in comparison with a healthy subject of the same age and gender
By definition, the Hb is reduced
The RBC and the Hct/PCV are usually also reduced
Other than a reduction in the absolute amount of haemoglobin in the blood stream, what else could cause anaemia? Why would this anaemia only be transient in the individual?
An increase in the plasma volume can decrease the haemoglobin concentration
The excess fluid would be excreted in a healthy individual
What is anaemia usually due to
Anaemia is usually due to a reduction of the absolute amount of haemoglobin in the blood stream
Occasionally it results from an increase in the volume of plasma rather than a decrease in the amount of haemoglobin
In a healthy person, anaemia resulting from an increase in plasma volume cannot persist because the excess fluid in the circulation is excreted
For practical purposes, anaemia can therefore be regarded as a resulting from a decrease of the absolute amount of haemoglobin in the circulation
What is the difference between a mechanism and a cause
Cause- something underlying
Mechanism- how it happens
Broadly speaking, state four mechanisms of anaemia
Reduced production of red cells/haemoglobin in the bone marrow
Loss of blood from the body (haemorrhage)
Reduced survival of red cells in the circulation (haemolytic- to the extent that the bone marrow cannot keep up)
Pooling of red cells in a very large spleen
How can we distinguish the mechanism from the cause
We need to distinguish the mechanism of anaemia from the cause
The mechanism of the anaemia might be reduced synthesis of haemoglobin in the bone marrow
The cause of this could be either a condition causing reduced synthesis of haem or one causing reduced synthesis of globin
Can you name one cause of reduced synthesis of haem?
Iron deficiency
What do you call a condition in which there is an inherited defect leading to reduced synthesis of globin?
Thallaseamia- genetic mutation- defect in synthesis of globin chains
What can we do when nor the mechanism nor the cause of anaemia are immediately apparent
Sometimes neither the mechanism of the anaemia or the specific cause is immediately apparent
Classification on the basis of cell size can help to suggest specific causes
How can we classify anaemias based on RBC size
Microcytic (usually also hypochromic)
Normocytic (usually also normochromic)
Macrocytic (usually also normochromic)
Normochromic as no defect in haemoglobin synthesis
Describe the common causes of microcytic anaemia
Common causes of a microcytic anaemia
Defect in haem synthesis
Iron deficiency
Anaemia of chronic disease
Defect in globin synthesis (thalassaemia)
Defect in α chain synthesis (α thalassaemia)
Defect in β chain synthesis (β thalassaemia)
Can affect gamma chain synthesis in the foetus too
Describe anaemia of chronic disease
Anaemia in chronic infection or inflammation- T.B or rheumatoid arthritis
Starts as normocytic and normochromic- but then becomes microcytic and hypochromic
Fe trapped in macrophages as haemocidirin- not mobilised and so can’t be synthesised into Hb
Describe a common cause of macrocytic anaemia
Macrocytic anaemias usually result from abnormal haemopoiesis so that the red cell precursors continue to synthesize haemoglobin and other cellular proteins but fail to divide normally
As a result, the red cells end up larger than normal
Describe megaloblastic erythropoiesis
A macrocytic anaemia is one in which average cell size is increased
One cause of this is megaloblastic erythropoiesis
This refers specifically to a delay in maturation of the nucleus (defect in synthesis of DNA) while the cytoplasm continues to mature and the cell continues to grow
All megaloblastic erythropoiesis anaemias are macrocytic
But not all macrocytic anaemias are megaloblastic
Megaloblasts are different from normoblasts and their nucleus does not condense properly
What is a megaloblast
A megaloblast is an abnormal bone marrow erythroblast
It is larger than normal and shows nucleo-cytoplasmic dissociation
It is possible to suspect megaloblastic anaemia from the peripheral blood features but to be sure requires bone marrow examination
Peripheral blood features include anaemia, macrocytes, ovalocytes and tear drop cells
Hyper-segmented neutrophils
If these features are found with a VitB12 or folic acid deficiency- suspect mealoblastic anaemia and treat accordingly (no need for bone marrow exam to confirm)
How will megaloblasts show on the blood film
Not well condensed nucleus in smaller, mature cells
Mature cells will be pinker (due to Hb)
Dyserythropiesis- abnormal erythropoiesis- 3 lobed nucleus
Gold standard for diagnosing megaloblastic anaemia
Describe another cause of macrocytic anaemia
An alternative mechanism of macrocytosis is premature release of cells from the bone marrow
Young red cells are about 20% larger than mature red cells so if there is an increased proportion of young red cells (reticulocytes) in the circulation, the average cell size (MCV) will be increased
Normal level of reticulocytes is 2%
Polychromasia on blood film will indicate presence of reticulocytes
List some causes of macrocytic anaemia
Megaloblastic anaemia as a result of lack of vitamin B12 or folic acid
Use of drugs interfering with DNA synthesis (methotextrate targets folic acid and many other chemotherapeutic agents target DNA synthesis)
Liver disease and ethanol toxicity (doesn’t result in megaloblastic anaemia as DNA synthesis not affected)
Recent major blood loss with adequate iron stores (reticulocytes increased) (if you’ve lost blood, the bone marrow will start spitting out reticulocytes to compensate Haemolytic anaemia (reticulocytes increased)- red cells lyse- (reticulocytosis due to the loss of red cells)
State the mechanisms of normocytic normochromic anaemia
§ Recent blood loss – i.e. peptic ulcer, trauma, G.I bleed- no time for bone marrow to compensate
§ Failure of production of red cells – i.e. beginning of iron deficiency, renal failure, bone marrow failure or suppression, bone marrow infiltration- failure of haematopoietic stem cell action
§ Pooling of red blood cells in the spleen – i.e. hypersplenism from portal cirrhosis.
Splenic sequestration of sickle cells- trapped in spleen- causing splenomegaly and acute drop in Hb
Outline the causes of macrocytic anaemia
Peptic ulcer, oesophageal varices, trauma
Failure of production of red cells
Early stages of iron deficiency or anaemia of chronic disease (eventually MCV decreases and cell becomes microcytic AS STORES DECREASE)
Renal failure (reduced EPO)
Bone marrow failure (reduced number of stem cells) or suppression (drugs may interfere with bone marrow function- but don’t alter DNA synthesis)
Bone marrow infiltration (cancer spread to bone marrow- reactive fibrosis)
Hypersplenism, e.g. portal cirrhosis
Define what is meant by haemolytic anaemia
Haemolytic anaemia is anaemia resulting from shortened survival of red cells in the circulation (less than 120 days and bone marrow cannot cope)
Haemolysis can result from an intrinsic abnormality of the red cells
Haemolysis can result from extrinsic factors acting on normal red cells
Haemolytic anaemia can also be classified as inherited or acquired
Describe inherited haemolytic anaemia
Inherited haemolytic anaemia can result from abnormalities in the cell membrane (hereditary spherocytosis or elliptocytosis_
, the haemoglobin (sickle cell)
or the enzymes in the red cell ( production of ATP in embden-myerhof pathway) or pentose shunt- not enough reductive power to prevent cell against oxidation
Describe acquired haemolytic anaemia
Acquired haemolytic anaemia usually results from extrinsic factors such as micro-organisms, chemicals or drugs that damage the red cell
Extrinsic factors can interact with red cells that have an intrinsic abnormality
How else can haemolytic anaemias be classified
Haemolytic anaemia can also be classified as intravascular or extravascular
Intravascular haemolysis occurs if there is very acute damage to the red cell (haemolysis within circulation)
Extravascular haemolysis occurs when defective red cells are removed by the spleen (or other macrophages of reticulo-endothelial system)
Often haemolysis is partly intravascular and partly extravascular
State some inherited abnormalities that can cause haemolytic anaemia.
Abnormal red cell membrane
Abnormal haemoglobin
Defect in the glycolytic pathway (pyruvate kinase deficiency)
Defect in the enzymes of the pentose shuttle (G6PD deficiency -common worldwide)
State some acquired abnormalities that cause haemolytic anaemia.
Damage to the red cell membrane (autoimmune haemolytic anaemia- splenic macrophages recognise antibodies that bind to antigens on RBC, snake bites- toxins that destroy RBC membrane) Damage to the whole red cell (microangiopathic haemolytic anaemia- small blood vessels- deposition f fibrin strands which trap the red cells and tear them into pieces- or damage to endothelium- and RBC are attached and torn off) Oxidant exposure (can damage membrane or oxidise Hb to MethHb which can't transport oxygen) - anti-malarial drugs (dapsone and primaquine can cause this)
Describe the interaction between inherited defects and extrinsic factors
G6PD is part of the pentose phosphate pathway
This is the only source of reduced glutathione in red blood cells
Because of the oxygen-carrying role of red blood cells, they are at constant risk of oxidant damage
So people with G6PD deficiency are at risk of haemolytic anaemia in states of oxidative stress
Need to be careful of certain drugs (anti-malarials) and avoid eating broad beans
What do we need to know about haemolytic anaemias
There are many causes of haemolytic anaemia
All you need to know is
How to suspect or recognise haemolytic anaemia
The features of a few common and important causes of haemolytic anaemia
When should we suspect a haemolytic anaemia
Otherwise unexplained anaemia, which is normochromic and usually either normocytic or macrocytic (high reticulocyte count)
Evidence of morphologically abnormal red cells (spherocytosis, fragments- MIHA, sickle cells)
Evidence of increased red cell breakdown (increased BR, unconjugated if liver can’t cope, LDH increases as present at high conc in RBCs, gallstones in adolescents- increased BR load)
Evidence of increased bone marrow activity (high reticulocyte count)
How can HbC and HbS appear on the blood film
HbC- square/rectanglular crystals
HbS– curved cells
How do BR gallstones show on the cholecystogram
Negative images-dark
Gallstones (old age)- calcium and so appear white
How can AIHA lead to spherocytosis
When spleen macropahges are breaking down RBCs- may only take a chunk out of them- cell no longer disc shaped- needs to round up to contain cytoplasm.
State examples of inherited diseases causing haemolytic anaemia that have defects at the following sites:
a. Membrane Hereditary spherocytosis b. Haemoglobin Sickle cell anaemia c. Glycolytic Pathway Pyruvate kinase deficiency d. Pentose Shunt G6PD deficiency
State examples of acquires disease causing haemolytic anaemia that have defects at the following sites
a. Membrane – immune Autoimmune haemolytic anaemia (may be isolated or part of lupus) b. Whole red cell – mechanical Microangiopathic haemolytic anaemia c. Whole red cell – oxidant Drugs and chemicals d. Whole red cell – microbiological Malaria
Summarise hereditary spherocytosis
Haemolytic anaemia or chronic compensated haemolysis (by bone marrow) resulting from an inherited intrinsic defect of the red cell membrane
After entering the circulation the cells lose membrane in the spleen and thus become spherocytic
Bilayer of membrane- not tetherd to underlying cytoskeleton- easily lost
Cells are normocyitic upon release from bone marrow
Describe the complications of hereditary spherocytosis
Red cells become less flexible and are removed prematurely by the spleen – extravascular haemolysis
The bone marrow responds to haemolysis by an increased output of red cells leading to polychromasia and reticulocytosis
Haemolysis leads to increased bilirubin production, jaundice and gallstones
What are the features of red cells in hereditary spherocytosis
They are LARGE and ROUND and have an increased MCHC
When are spherocytes more prone to haemolysis
Spherocytes are also more prone to haemolyse when osmotic pressure is reduced
So, in osmotic fragility test- as you increase the conc of NaCl- you get less haemolysis.
Describe the treatment for hereditary spherocytosis
The only effective treatment is splenectomy, but this has its own risks so is only done in severe cases
A good diet is important so that a secondary folic acid deficiency does not occur
Alternatively, one folic acid tablet can be taken daily
Summarise GPPD
G6PD is an important enzyme in the pentose phosphate shunt
It is essential for the protection of the red cell from oxidant damage
Oxidants may be generated in the blood stream, e.g. during infection, or may be exogenous
What causes the haemolysis in G6PD
Extrinsic oxidants may be foodstuffs (e.g. broad beans), chemicals (e.g. naphthalene) or drugs (e.g. dapsone, primaquine)
The gene for G6PD is on the X chromosome so affected individuals are usually hemizygous males (but occasionally homozygous females)
Why is a good diet important in patients with hereditary spherocytosis
They have increased bone marrow activity and erythropoiesis so they need a supply of B12, folate and iron to keep producing red blood cells
What is important to remember about the nature of intravascular haemolysis in G6PD
G6PD deficiency usually causes intermittent, severe intravascular haemolysis as a result of infection or exposure to an exogenous oxidant
What are the key features on the blood film during an episode of intravascular haemolysis in G6PD
These episodes of intravascular haemolysis are associated with the appearance of considerable numbers of irregularly contracted cells
Haemoglobin is denatured and forms round inclusions known as Heinz bodies, which can be detected by a specific test
How are Heinz bodies removed
Heinz bodies are removed by the spleen, leaving a defect in the cell
Froming bite cells/keratocytes
Describe the importance of prevention in G6PD
Acute haemolysis sometimes requires blood transfusion
Thereafter, prevention is important
Dietary and drug restriction
Cards alerting their deficiency
What happens in autoimmune haemolytic anaemia
Autoimmune haemolytic anaemia results from production of autoantibodies directed at red cell antigens
The immunoglobulin bound to the red cell membrane is recognized by splenic macrophages, which remove parts of the red cell membrane, leading to spherocytosis
Complement components can also be bound to the immunoglobulin molecule, and they are also recognised by receptors on splenic macrophages
What blood film features will be seen in autoimmune haemolytic anaemia
Anaemia and spherocytosis in autoimmune haemolytic anaemia
What is important to remember about the spherocytes in autoimmune haemolytic anaemia
The spherocytes are less flexible than normal red cells
The combination of cell rigidity and recognition of antibody and complement on the red cell surface by splenic macrophages leads to removal of cells from the circulation by the spleen
Describe the diagnosis of autoimmune haemolytic anaemia
Diagnosis is by
Finding spherocytes and an increased reticulocyte count
Detecting immunoglobulin ± complement on the red cell surface
Detecting antibodies to red cell antigens or other autoantibodies in the plasma
Describe the treatment of autoimmune haemolytic anaemia
Treatment is by
Use of corticosteroids and other immunosuppressive agents
Splenectomy for severe cases
Summarise the treatment for microangiopathic haemolytic anaemia
Treatment may be by
Removing the cause, e.g. treating severe hypertension or stopping a causative drug
Plasma exchange when it is caused by an antibody in the plasma that is leading indirectly to fibrin deposition
Thrombotic thrymobocytopenic purura- damages platelets – due to antibody against platelets
What can aid the diagnosis of haemolytic anaemia
The detection of morphologically abnormal red cells, e.g. spherocytes, elliptocytes, fragments.
Evidence of increased red cell breakdown, e.g. increased serum bilirubin (unconjugated) and lactate dehydrogenase (LDH).
Evidence of an increased bone marrow response, e.g. polychromasia and an increased reticulocyte count.
Draw schemata for the mechanisms of intravascular and extravascular haemolysis
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