Anaemia Flashcards

1
Q

What is anaemia

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

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2
Q

What in a FBC is reduced in anaemia

A

Hb

Usually RBC and Hct

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3
Q

What may anaemia be a result of

A

Reduction in the absolute amount of haemoglobin in the blood stream
Occasionally due to an increase in volume plasma (cannot persist as excess fluid is excreted)

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4
Q

What are the mechanisms of anaemia

A

Reduced production of red cells/haemoglobin in the bone marrow
Loss of blood from the body
Reduced survival of red cells in the circulation
Pooling of red cells in a very large spleen

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5
Q

What are the causes of microcytic anaemia

A

Defect in haem synthesis

  • iron deficiency
  • anaemia of chronic disease

Defect in global synthesis (thalassaemia)

  • Defect in α chain synthesis
  • Defect in β chain synthesis
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6
Q

Describe macrocytic anaemia

A

Average cell size is increased
Usually result from abnormal haemopoiesis
The red cell precursors continue to synthesise haemoglobin and other cellular proteins but fail to divide normally

May be due to premature release of cells from bone marrow (20% larger)

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7
Q

What is megaloblastic erythropoiesis

A

A cause of macrocytic anaemia

Delay in maturation of the nucleus while the cytoplasm continues to mature and the cell continues to grow

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8
Q

What is a megaloblast

A

Abnormal bone marrow erythroblast

Larger than normal and shows nuclei-cytoplasmic dissociation

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9
Q

What are the common causes of macrocytic anaemia

A

Megaloblastic anaemia as a result of lack of vitamin B12 or folic acid
Use of drugs interfering with DNA synthesis
Liver disease and ethanol toxicity
Recent major blood loss with adequate iron stores (increased reticulocytes)
Haemolytic anaemia (increased reticulocytes)

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10
Q

What are the mechanisms of normocytic anaemia

A

Recent blood loss
Failure of production of red cells
Pooling of red cells in the spleen

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11
Q

What are the causes of normocytic normochromic anaemia

A

Peptic ulcer, oesophageal varices, trauma
Failure of production of red cells
Hypersplenism e.g. portal cirrhosis

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12
Q

Describe haemolytic anaemia

A

Resulting from shortened survival of red cells in the circulation
May be due to intrinsic abnormality of the red cells or extrinsic factors acting on normal red cells

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13
Q

What is the difference between inherited and acquired haemolytic anaemia

A

Inherited - can result from abnormalities in the cell membrane, haemoglobin or enzymes in the red cell

Acquired - usually results from extrinsic factors such as micro-organisms, chemicals or drugs that damage the red cell

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14
Q

What is the difference between intravascular and extravascular haemolysis

A

Haemolysis is partly intravascular and partly extravascular

Intravascular - if there is very acute damage to the red cell

Extravascular - Defective red cells are removed by the spleen

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15
Q

Give examples of causes of inherited haemolytic anaemia

A

Cell membrane - Hereditary spherocytosis

Haemoglobin - Sickle cell

Glycolytic pathway - pyruvate kinase deficiency

Enzymes of pentose shunt - G6PD deficiency

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16
Q

Give examples of causes of acquired haemolytic anaemia

A

Cell membrane - Autoimmune haemolytic anaemia or snake bite
Whole cell - Microangiopathic haemolytic anaemia, malaria
Oxidant exposure - damson or primaquine

17
Q

How may acquire haemolytic anaemia cause inherited anaemia

A

Precipitation of episodic haemolysis in individuals with an enzyme deficiency (from oxidant exposure damage) can cause a defect in enzymes of the pentose shunt

18
Q

When should haemolytic anaemia be expected

A

Otherwise unexplained anaemia (normochromic and normocytic/macrocytic)
Evidence of morphologically abnormal red cells
Evidence of increased red cell breakdown
Evidence of increased bone marrow activity

19
Q

Describe hereditary spherocytosis

A

Haemolytic anaemia or chronic compensated haemolysis 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

20
Q

How does hereditary spherocytosis lead to jaundice

A

Spherocytes are less flexible and are removed prematurely by the spleen (extravascular haemolysis)
The bone marrow responds nay increasing output of red cells, leading to polychromasia and reticulocytosis
Leads to increased bilirubin production, jaundice and gall stones

21
Q

What is the osmotic fragility test

A

Spherocytes are more prone to haemolyse when osmotic pressure is reduced

22
Q

How is hereditary spherocytosis treated

A

Splenectomy
Good diet so secondary folic acid deficiency does not occur
One folic acid tablet taken daily

23
Q

Describe glucose-6-phosphate dehydrogenase deficiency

A

G6PD is an important enzyme in the pentose phosphate shunt
Essential for the protection of the red cell from oxidant damage
Gene for G6PD is on the X chromosome so those affected are usually homozygous males (sometimes homozygous females)

24
Q

What causes oxidant damage

A

Oxidants may be generated in the blood stream e.g. during infection, or may be exogenous
extrinsic - broad beans
intrinsic - naphthalene in mothballs
Drugs - dapsone, primaquine

25
Q

What does G6PD deficiency cause

A

Intermittent severe intravascular haemolysis as a result of infection or exposure to an exogenous oxidant
Such episodes are associated with irregularly contracted cells
Haemoglobin is denatured and forms Heinz bodies (round inclusions)

26
Q

Describe autoimmune haemolytic anaemia

A

Results from production of autoantibodies directed at red cell antigens
Immunoglobulins bound to red cell membrane is recognised by splenic macrophages, which removes parts of the red cell membrane -> spherocytosis
Complements can be bound to the Ig molecule and recognised by splenic macrophages

27
Q

How does autoimmune haemolytic anaemia -

A

Spherocytes are less flexible
Combination of cell rigidity and recognition of antibody and complement on the red cell surface by splenic macrophages leads to removal of cells by the spleen

28
Q

How is autoimmune haemolytic anaemia diagnosed

A

Spherocytes found
Increased reticulocyte count
Immunoglobulin and complement on red cell surface detected
Antibodies to red cell antigens or other autoantibodies in the plasma detected

29
Q

How is autoimmune haemolytic anaemia treated

A

use of corticosteroids and other immunosuppressive agents

Splenectomy for severe cases

30
Q

How is microangiopathic haemolytic anaemia treated

A

Remove the cause e.g. treat 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

31
Q

What can cause failure of production of red cells

A
  • Early stages of iron deficiency or anaemia of chronic disease
  • renal failure
  • bone marrow failure or suppression
  • bone marrow infiltration