Session 4: Introduction to Anaemia, B12 and Folate Metaboism and Megaloblastic Anaemia

Question 1

Define anaemia.

Answer 1

Haemoglobin concentration below the reference range for the normal population.

Question 2

What make the normal range of haemoglobin vary?

Answer 2

Age Sex Ethnicity etc…

Question 3

Symptoms of anaemia.

Answer 3

• Shortness of breath • Tiredness • Cardiac failure • Palpitations • Headache

Question 4

Clinical signs of anaemia.

Answer 4

• Pallor • Tachycardia • Tachypnoea • Hypotension

Question 5

Specific signs of: • Iron deficiency • Vit B12 deficiency • Thalassaemia

Answer 5

ID: Koilonychia, oesophageal webs, angular stomatitis Vit B12 D: Glossitis Thalassaemia: abnormal facial bone development

Question 6

What are the different stages in the physiological life cycle of RBCs that can cause anaemia?

Answer 6

Alteration of erythropoiesis Alteration of haemoglobin synthesis Function and metabolism in the RBCs Structure of the RBCs Alteration in the reticule-endothelial system Loss of red cells

Question 7

What is dyserythropoiesis?

Answer 7

Reduced erythropoiesis and production of RBCs.

Question 8

Explain the hormonal control of erythropoiesis.

Answer 8

As patient becomes anaemic the reduced pO2 is detected in interstitial peritubular cells in the kidneys. This causes an increased production of erythropoietin by the kidneys. Erythropoietin stimulates maturation and release of RBCs form bone marrow. Number of RBCs increase and rise in haemoglobin. More O2 can be delivered and via a feedback loop as pO2 increases again erythropoietin production decreases.

Question 9

How can there then be a reduction in erythropoiesis causing anaemia?

Answer 9

Response from kidneys is inadequate - chronic kidney disease e.g. Empty bone marrow so erythropoietin has no effect. This can be after chemotherapy or infection from parvovirus or aplastic anaemia. If the marrow is infiltrated by cancer cells or fibrous tissue normal haemopoietic cells might be reduced.

Question 10

What would cause defects in haemoglobin synthesis? In what way?

Answer 10

Deficiencies in essential nutrients such as iron deficiency causing deficiency in Haem synthesis. Anaemia of chronic disease causing a lack in functional iron. Lack of B12 and/or folate causing a deficiency in the building blocks for DNA synthesis, this can cause megaloblastic anaemia. Mutations in the proteins that encode for the global chains like Thalassaemias and sickle cell disease.

Question 11

Give examples of hereditary diseases that are caused by defects in red cell membrane structure.

Answer 11

Hereditary spherocytosis Hereditary elliptocytosis Hereditary pyrpoikilocytosis

Question 12

Except for hereditary diseases, how can there be a defect in the red cell membrane structure?

Answer 12

Mechanical damage to the RBCs: Heart valves causing rupture of the RBCs in the case of stenosis. Vasculitis MAHA DIC Heat damage causing direct damage Osmotic changes when you are drowning.

Question 13

Explain what defects in red cell metabolism means.

Answer 13

When there is an enzyme in red blood cells that is defected which can lead to anaemia.

Question 14

Give examples of such enzymes.

Answer 14

Glucose-6-Phosphate dehydrogenase Pyruvate kinase deficiency

Question 15

Give an external cause of anaemia.

Answer 15

Loss of blood such as a cut, menstruation etc.

Question 16

What makes the reticuloendothelial system increase in activity?

Answer 16

The RES which consists of the spleen and other tissues removes damaged or defective red cells. It will do this in many of the causes listed in previous flashcards such as membrane disorders, enzyme disorders and haemoglobin disorders.

Question 17

Which anaemias tend to cause a more rapid destruction of red blood cells? Why?

Answer 17

Haemolytic anaemias since they are abnormal and/or damaged.

Question 18

Where does the destruction and digestion of RBCs occur?

Answer 18

Can be both intravascular in the blood and extravascular such as the spleen, liver and bone marrow.

Question 19

Give an example of an autoimmune disease causing increased RES activity.

Answer 19

Autoimmune Haemolytic anaemia. Autoantibodies bind to red cell membrane proteins, RES cells (macrophages) recognise the cells as defective (even though they aren’t). The macrophages attach to it and then either removes the autoantibody which can tear off a bit of the red blood cell resulting in a smaller cell and defective, or it can digest it as a whole immediately.

Question 20

Explain how myelofibrosis causes anaemia.

Answer 20

Erythropoiesis goes down as the marrow is fibrotic so there is little space for haemopoiesis. Also there will be defective RBCs leading to increased removal so increased activity of RES.

Question 21

Explain how thalassemia can cause anaemia.

Answer 21

Haemoglobin synthesis is ineffective leading to a malformed RBC. RES then increases in activity to remove structurally defective RBCs.

Question 22

How can anaemia be evaluated? (In order to find the underlying cause)

Answer 22

By the mechanism of the anaemia By the size of the RBCs whether they are microcytic, normocytic or macrocytic. By presence or absence of reticulocytosis (doing a reticulocyte count)

Question 23

What does a high reticulocyte count entail? What does a low count mean?

Answer 23

High: bone marrow is working properly Low: Bone marrow is not working properly

Question 24

If the bone marrow is working properly but the patient is still anaemic. What is the next step we need to ask?

Answer 24

Whether there is evidence of haemolysis.

Question 25

If there is evidence of haemolysis, what is the next step?

Answer 25

To evaluate the size of the red blood cells, whether they are microcytic, macrocytic or normocytic.

Question 26

If there is no evidence of haemolysis, what is the next step?

Answer 26

We assume there is a bleed because there is no haemolysis going on and bone marrow is working properly. So we look for evidence of bleeding.

Question 27

If the bone marrow is not working properly, what is the next step?

Answer 27

To evaluate the size of the red blood cells.

Question 28

In anaemia with reticulocytosis, what are the most common causes?

Answer 28

Acute blood loss Splenic sequestration Haemolysis: Immune mediated (autoimmune or drug related) Non-immune - Mechanical damage (stenosis, MAHA), Haemoglobinopathies, Enzyme defects, membrane defects

Question 29

In case of anaemia with low reticulocyte count that have a low MCV and therefore microcytic. What are the most common causes?

Answer 29

TAILS: Thalassemia trait Anaemia of chronic disease (usually normocytic) Iron deficiency Lead poisoning Sideroblastic anaemia

Question 30

In case of anaemia with low reticulocyte count that have a a high MCV and therefore macrocytic. What are the most common causes?

Answer 30

Vitamin B12 deficiency Folate deficiency Myelodysplasia Liver disease Hypothyroidism Alcohol

Question 31

In case of anaemia with low reticulocyte count that have a a normal MCV and therefore normocytic. What are the most common causes?

Answer 31

Primary bone marrow failure (which is very rare): Aplastic anaemia and red cell aplasia Secondary bone marrow failure (much more common): Anaemia of chronic disease Combined haematinic deficiencies Uraemia Endocrine abnormalities HIV infection

Question 32

Very briefly outline what happens in vitamin B12 and/or folate deficiency.

Answer 32

Deficiency in building blocks for DNA synthesis -> RBCs become enlarged -> macrocytic anaemia. This type of macrocytic anaemia is called megaloblastic anaemia.

Question 33

Explain Vitamin B12 (cyanocobalime) absorption.

Answer 33

Orally ingested from foods of anima origin. Salivary glands secreted haptocorrin (HC) which binds to B12. Goes into the stomach - the stomach’s parietal cells release intrinsic factor (IF) Well in the small intestine the B12 dissociates from the HC and binds to IF instead. The IF-B12 complex binds to receptors in the terminal ileum. B12 is absorbed here and IF is destroyed.

Question 34

Give causes of low B12.

Answer 34

Vegan or poor diet. No intrinsic factor (pernicious anaemia or gastrectomy) Disease of the ileum like Crohn’s, ileal resection and tropical sprue inhibiting absorption. Lack of transcobalamin (congenital)

Question 35

In what food can folate be found? Where is it absorbed? What is the normal range and how long is it stored?

Answer 35

Most foods - mainly yeast, liver and leafy greens Absorbed in duodenum and jejunum 5 mg stores for about 3-4 months.

Question 36

Give causes of folate deficiency.

Answer 36

Poor diet Increased use of folate such as: pregnancy, increased erythropoiesis in haemolytic anaemia, severe skin disease.

Disease of the duodenum and jejunum

Lack of methylTHF - inhibits dihydrofolate reducatase enzyme

Alcoholism

Liver disease

Heart failure

Question 37

Explain the Vit B12/folate link.

Answer 37

B12 and folate depend on each other to work. Folate needs B12 to become active. B12 needs folate to become methylated so it can convert homocysteine to methionine, this converts folate back into its active form tetrahydrofolate.

Vitamin B12 reactivates folic acid back into tetrahydrofolate.

Low B12 casues a functional folate deficiency.

Question 38

How does B12 and folate deficiency cause megaloblastic anaemia?

Answer 38

Leads to thymidylate deficiency.

In absence of thymine, uracil will be incorporated into DNA instead.

DNA repair enzymes detect the error and DNA strands are destroyed.

Causes asynchronous maturation between nucles and cytoplasm of the RBCs. Nucleus doesnt fully mature and becomes inappropriately large. The chromatin is also open.

However the cytoplasm matures at a normal rate.

Question 39

Histological features of B12 and/or folate deficiency.

Answer 39

Macrocytic red cells

Anoisopoikilcytosis with tear drops

Hypersegmented neutrophils

As deficiency progesses panocytopenia can develop.

Question 40

What are complications of B12 or folate deficiency?

Answer 40

Can lead to neurological disease.

B12 (not folate) deficiency leads to focal demyelination affecting the spinal cord, peripheral nerves and optic nerves.

Folate deficiency in pregnancy can cause neural tube defects.

Question 41

How would you investigate megaloblastic anaemia?

Answer 41

FBC

B12 levels

Serum folate

Check bilirubin and LDH.

Blood film for investigating size

Question 42

What would the different tests show in case of megaloblastic anaemia?

Answer 42

FBC - low Hb and high MCV

Blood film - megaloblastic features

Bilirubin and LDH should be high

B12 and folate low.

Question 43

Would you do any other subsequent tests?

Answer 43

B12 is a poor test so if it is borderline repeat it.

Otherwise you can check for plasma total homocysteine and/or plasma methylmalonic acid.

Also check for anti-intrinsic factor antibodies.

Question 44

How would you treat B12/folate deficiency.

Answer 44

The first thought would be supplements or dietary change.

Oral folic acid

Oral cyanocobalamine (B12) or just eat more meat.

If the defiency is not dietary:

Pernicious anaemia -> intramuscular injection of B12

Question 45

Why would you be careful before giving a transfusion to an anaemic patient?

Answer 45

Because B12 deficient patients that receive transfusion can develop high output cardiac failure.