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Year 2 - MCD - Haematology > Anaemia and Polycythaemia > Flashcards

Anaemia and Polycythaemia Flashcards

21.10.2019

1
Q

What is anemia?

A
  • reduced Hb
  • low Hb in a given BV compared to healthy individuals of same age and same gender
  • usually accompanied by low RBC and Hct/PCV
  • usually due to reduction of absolute Hb in blood
  • sometimes a problem with high plasma volume rather than low Hb itself
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2
Q

Anemia due to increased plasma volume

A
  • 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
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3
Q

What are the 4 mechanisms of anemia?

A
  1. Reduced production of red cells/haemoglobin in the bone marrow
  2. Loss of blood from the body
  3. Reduced survival of red cells in the circulation
  4. Pooling of red cells in a very large spleen
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4
Q

Mechanism vs. cause of anemia

A
  • 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
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5
Q

Can you name one cause of reduced synthesis of haem?

A

Iron deficiency

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6
Q

What do you call a condition in which there is an inherited defect leading to reduced synthesis of globin?

A

Thalassemia

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7
Q

How do you determine the cause of anemia?

A
  • 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
  • also patient history incl. diet, FH etc.
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8
Q

Anemia classification based on cell size?

A
  • Microcytic (usually also hypochromic)
  • Normocytic (usually also normochromic)
  • Macrocytic (usually also normochromic)
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9
Q

Common causes of microcytic anaemia?

A

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)
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10
Q

Common causes of macrocytic anaemia?

A
  • Macrocytic anaemias usually result from ABNORMAL HAEMOPOIES so that the red cell precursors continue to synthesize Hb and other cellular proteins but fail to divide normally
  • b12 def, folic acid def
  • As a result, the red cells end up larger than normal
  • another cause is premature release of RBCs 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
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11
Q

Microcytic vs. Megaloblastic

A
  • microcytic simply means that the average cell size is increased
  • one cause of this is megaloblastic erythropoiesis
  • This refers specifically to a delay in maturation of the nucleus while the cytoplasm continues to mature and the cell continues to grow
  • megaloblastic anemics are macrocytic but not all microcytic anemias are megaloblastic
  • It is possible to suspect megaloblastic anaemia from the peripheral blood features but to be sure requires bone marrow examination
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12
Q

What is megaloblastic erythropoiesis?

A
  • A delay in maturation of the nucleus while the cytoplasm continues to mature and the cell continues to grow
  • due to a defect in DNA synthesis
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13
Q

What is a megaloblast?

A
  • 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
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14
Q

What are the differences between normoblasts and megaloblasts on a blood film?

A
  • megaloblasts are larger
  • nucleus is not condensed in the megaloblasts
  • heamoglobinised cytoplasm
  • dyserythropoiesis - erythropoiesis looks abnormal e.g. nucleus with 3 lobes
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15
Q

Size difference between mature and immature red cells

A
  • 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
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16
Q

Specific 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 (reticulocytes increased)
  • Haemolytic anaemia (reticulocytes increased)
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17
Q

Mechanisms of normocytic normochromic anemia?

A
  • Recent blood loss
  • Failure of production of red cells
  • Pooling of red cells in the spleen
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18
Q

Causes of normocytic normochromic anemia?

A

Peptic ulcer, oesophageal varices, trauma

Failure of production of red cells

  • Early stages of iron deficiency or anaemia of chronic disease
  • Renal failure
  • Bone marrow failure or suppression
  • Bone marrow infiltration

Hypersplenism, e.g. portal cirrhosis

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19
Q

What is haemolytic anaemia?

A
  • Haemolytic anaemia is anaemia resulting from shortened survival of red cells in the circulation
  • Haemolysis can result from an intrinsic abnormality of the red cells
  • Haemolysis can result from extrinsic factors acting on normal red cells
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20
Q

How can hamolytic anemia be classified?

A
  • intrinsic vs. extrinsic
  • inherited vs. acquired
  • intravascular vs. extravascular haemolysis
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21
Q

Inherited vs. acquired haemolytic anaemia

A
  • Inherited haemolytic anaemia can result from abnormalities in the cell membrane, the haemoglobin or the enzymes in the red cell
  • 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 which makes them more susceptible
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22
Q

Intravascular vs. extravascular haemolytic anemia

A
  • Intravascular haemolysis occurs if there is very acute damage to the red cell, occurs in the circulation
  • Extravascular haemolysis occurs when defective red cells are removed by the spleen
  • Often haemolysis is partly intravascular and partly extravascular
23
Q

Intrinsic vs. extrinsic haemolytic anaemia

A
  • Haemolysis can result from an intrinsic abnormality of the red cells
  • Haemolysis can result from extrinsic factors acting on normal red cells
24
Q

What is the life span of RBCs in SCA?

A

~20 d

25
Q

Name the specific causes of inherited haemolytic anaemia

A
  • abnormal cell membrane e.g. in hereditary spherocytosis or elliptocytosis
  • abnormal Hb e.g. SCA
  • defect in glycolytic pathway e.g. pyruvate kinase deficiency
  • defect in enzymes of pentose shunt (e.g. glucose-6-phosphate dehydrogenase (G6PD) deficiency)
26
Q

Name the specific causes of acquired haemolytic aenemia

A
  • damage to the cell membrane e.g. AIHA (ABs against antigens on own red cells, immunoglobulin is recognised by spenlic macrophage and AB-coated cells are removed by the spleen) or snake bite (certain snake bites have toxins that damage the cell membrane and cause haemolysis)
  • damage to the whole RBC e.g. MAHA (M
  • oxidant exposure, damage to RBC membrane and Hb e.g. dapsone and primaquine (here there is interplay with acquired: G6PD and other problems with the pentose shunt are prone to oxidative damage because they lack the enzyme to protect the cell)
27
Q

What is the most important enzyme defect in the pentose shunt on a worldwide basis?

A
  • glucose-6-phosphate dehydrogenase deficiency

- very common in a number of ethnic groups

28
Q

MAHA

A

= microangiopathic haemolytic anaemia

  • damage occurring in small blood vessles leading to haemolysis
  • maybe deposition of fibrin strands which trap the RBCs and tear them into pieces
  • or damage to endothelium (RBCs stir to the endothelium, are torn off and rupture)
29
Q

When should you suspect haemolytic anaemia?

A
  • Otherwise unexplained anaemia, which is normochromic and usually either normocytic or macrocytic
  • Evidence of morphologically abnormal red cells
  • Evidence of increased red cell breakdown
  • Evidence of increased bone marrow activity
30
Q

dapsone and primaquine

A
  • anti malaria drugs
  • can cause damage to RBCs (cell membrane or Hb) due to oxidant exposure
  • G6PD and other deficiencies are prone to oxidant damage because they lack the enzyme needed to protect the cell -> interplay between inherited and acquired
31
Q

HbC

A 
Hemoglobin C (Hb C) is a structural variant of normal hemoglobin A (Hb A) caused by an amino acid substitution of lysine for glutamic acid at position six of the beta hemoglobin chain. 
- forms crystals? square/rectangular shape
32
Q

What kind of biliary problems might you have with haemolysis?

A
  • jaundice

- bilirubin gall stones (not Calcium like on the gallstones you get with age) due to chronic haemolysis

33
Q

How might AIHA present on a blood film?

A
  • polychromatic macrocytes
  • spherocytes (because sometimes the spleen does not remove the entire cell but just takes a bite of the AB coated membrane and the cell folds into a spherical shape.
34
Q

Examples of inherited haemolytic defects at different sites:

  • Membrane
  • Haemoglobin
  • Glycolytic pathway
  • Pentose shunt
A

Membrane - hereditary spherocytosis
Haemoglobin - SCA
Glycolytic pathway - pyruvate kinase deficiency
Pentose shunt - G6PD deficiency

35
Q

Examples of acquired haemolytic defect at different sites:

  • Membrane – immune
  • Whole red cell – mechanical
  • Whole red cell – oxidant
  • Whole red cell – microbiological
A

Membrane – immune: AIHA (can occur as an isolated AI disease or as a part of e.g. SLE)
Whole red cell – mechanical: MAHA (Microangiopathic haemolytic anaemia -> not common but important)
Whole red cell – oxidant: dugs and chemicals
Whole red cell – microbiological: Malaria (cells are parasitised and a lot of them are destroyed by macrophages)

36
Q

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
  • 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
  • osmotically fragile - burst more readily in the osmotic fragility test which looks at cells readiness to rupture in different concentrations of NaCl
37
Q

How do you treat hereditary spherocytosis?

A
  • The only effective treatment is splenectomy, but this has its own risks so is only done in severe cases (the spleen is important in protecting from malaria as well as various bacteria auch as pneumococcus and streptococcus) -> try to delay the splenectomy as much as possible e.g. only once the children are 5 or 6
  • A good diet is important so that a secondary folic acid deficiency does not occur (these people need more folic acid because bone marrow is super active in chronic haemolytic anaemia)
  • Alternatively, one folic acid tablet can be taken daily
38
Q

Why are people with hereditary spherocytosis given folic acid tablets? (or advised to have folic acid in their diet)

A
  • they have a higher requirement

- in chronic haemolytic anaemia the BM is super active and a lot of folate is needed

39
Q

Glucose-6-phosphate dehydrogenase (G6PD) deficiency

A
  • 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
  • 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)
  • G6PD deficiency usually causes intermittent, severe intravascular haemolysis as a result of infection or exposure to an exogenous oxidant
40
Q

What leads to haemolysis in G6PD deficiency?

A
  • e.g. broad beans (=fava beans)
  • e.g. naphthalene

=> cause oxidation, the cell cannot protect itself from oxidation, haemolysis occurs

41
Q

Blood film in G6PD deficiency?

A
  • 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
  • Heinz bodies are removed by the spleen, leaving a defect in the cell
42
Q

How do you treat G6PD deficiency?

A
  • Acute haemolysis sometimes requires blood transfusion
  • Thereafter, prevention is important - make them aware of their dietary restrictions and also abundance of drugs that cause haemolysis
43
Q

Bite cell / keratocyte

A

Only Heinz body was removed by the spleen

keratocyte is a cell with horns

44
Q

Heinz Body

A
  • inclusions within red blood cells composed of denatured Hb

- not visible with routine blood staining techniques, but can be seen with supravital staining.

45
Q

What is important when perscribing drugs to patients with G6PD deficiency?

A

There is a list of drugs that can cause hameolysis in these patients. You have to avoid these and check if a given drug can be given to that patient.

46
Q

AIHA

A
  • 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
  • anaemia and spherocytosis
  • happens in spleen but also liver and in other places where there are macrophages
47
Q

How do you diagnose AIHA?

A
  • 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
48
Q

How do you treat AIHA?

A
  • Use of corticosteroids and other immunosuppressive agents
  • Splenectomy for severe cases
49
Q

How do you treat MAHA?

A
  • Removing the cause (there are many causes, e.g. treating the systemic disease such as 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 (thrombocytopaenic purpura, excess fibrin deposition)
50
Q

A microcytic anaemia is likely to be due to

a) Vitamin B12 deficiency
b) Folic acid deficiency
c) Iron deficiency
d) Haemolysis
e) Acute blood loss

A

c) iron deficiency

51
Q

Polycythaemia in a patient seeing his general practitioner in London because of he has noticed his urine is red is most likely to be due to

a) Chronic renal failure
b) Living at high altitude
c) Hypoxia from chronic obstructive pulmonary disease
d) Haemolysis
e) Renal carcinoma

A

e) is correct - renal carcinoma

a) CRF will cause anaemia not polycythamia (because there is low EPO)
b) does not make sense in London
c) hypoxia from COPD possible but does not explain red urine
d) haemolysis won’t cause polycythamia (could cause red urine if there was free Hb after intravascular heamolysis)

52
Q

Polycythaemia

A
  • having a high concentration of red blood cells in your blood
  • This makes the blood thicker and less able to travel through blood vessels and organs. Many of the symptoms of polycythaemia are caused by this sluggish flow of blood
53
Q

Can you tell the difference between AIHA and hereditary spherocytosis on a blood film?

A

No. But you can generally tell from how the patient presents and from their history.

54
Q

Coombs test

A

to detect antibodies and complement on the surface of erythrocytes

Year 2 - MCD - Haematology (11 decks)

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