4a - Introduction to anaemia, B12 and folate

Question 1

What is aneamia?

Answer 1

Haemoglobin outside of the reference range for the normal population

Question 2

Identify some symptoms of anaemia

Answer 2

shortness of breath, tiredness, cardiac failure, palpitations, headache Sign of an underlying condition: pallor, tachycardia, tachypnoea, hypotension

Question 3

Identify the mechanisms of anaemia

Answer 3

1. Dyserythropoiesis 2. Haemoglobin synthesis 3. Loss of Blood 4. Overactive RES - (reticuloendothelial system)

Question 4

What Is erythropoiesis?

Answer 4

• Production of RBCs in the bone marrow. Initially begin as nucleated cells; nucleus becomes smaller and is extruded.
• Cytoplasm: blue and pink (as it becomes more haemoglobinsed)
• Enter circulation – for about 120 days
• Triggered by erythropoietin - produced by the kidney in response to low oxygen conditions

Question 5

What is the purpose of the RES?

Answer 5

Old and damaged RBCs are removed

Question 6

What is aplastic anaemia ?

Answer 6

Bone marrow and HPSCs are damaged which causes an inability of haematopoietic stem cells to generate mature blood cells

Question 7

How does reduced erythropoiesis arise?

Answer 7

• Kidney damage
• Chronic renal failure
• Aplastic anaemia

Question 8

How can myelofibrosis cause anaemia?

Answer 8

• Myelofibrosis is the production of collagen and fibrous tissue in the bone marrow reducing the space available for correct erythropoiesis to occur.
• This causes a reduction in the haemopoetic stem cells produced

Question 9

What is dyserythropoiesis?

Answer 9

• Defective red blood cell development
• Iron is not released for use in bone marrow
• Reduced lifespan of red cells
• The marrow shows a lack of response to erythropoietin.
• Seen in: Renal disease, inflammatory conditions such as Rheumatoid arthritis, SLE, Inflammatory bowel disease (Ulcerative Colitis or Crohn’s), chronic infections

Question 10

What are the mechanisms of anaemia?

Answer 10

Bone marrow:

• Abnormal erythropoeisis
• Abnormal Hb synthesis

Red blood cells

• Abnormal Function
• Structure

Metabolism Removal - Abnormal function of the RES

Question 11

What factors affect Hb synthesis

Answer 11

• Lack of iron (haem) - Lack of B12/ folate (DNA synthesis) - Mutations in globin chain synthesis

Question 12

Categorise abnormalities of red cell membranes

Answer 12

• Inherited (genetic) - Acquired

Question 13

Identify some inherited diseases which impact red cell membranes

Answer 13

• Thalassemia - Hereditary spherocytosis - Hereditary elliptocytosis

Question 14

Why do issues of metabolism in red cells arise in anaemia?

Answer 14

• Red cells need ATP to keep the membrane working properly - Lipid bilayer needs to be maintained! - Red cell enzyme defects can lead to anaemia

Question 15

Identify two metabolic disorders which result in anaemia ?

Answer 15

1. Glucose-6-phosphate dehydrogenase 2. Pyruvate kinase deficiency

Question 16

Identify some ACQUIRED abnormalities of the red cell membrane

Answer 16

• Heart valves – become lose, cells become sheared as they go through –> produces red cell fragments - Vasculitis - MAHA (microangiopathies) – little blood clos form in small vessels as RBCs try to pass by clots they become sheared - DIC – disseminated intravascular coagulopathy

Question 17

How do ACQUIRED abnormalities of the red cell membrane result in anaemia ?

Answer 17

• Mechanical damage to the red cells
• Cells taken out of the circulation

Question 18

How do impairment to the normal reticuloendothelial system result in anaemia?

Answer 18

• The spleen removes damaged (e.g. they don’t look right) or defective red cells
• It will do this in many of the causes of anaemia already covered e.g membrane disorders, enzyme disorders, haemoglobin disorders

Question 19

Identify three situations in which the RES removes red blood cells in anaemia

Answer 19

• Autoimmune haemolytic anaemia
• Haemolytic anaemia
• Myelofibrosis

Question 20

What is Haemolytic anaemia?

Answer 20

• RBCs destroyed more quickly as they are abnormal or damaged
• Intravascular - Can occur within the blood vessels
• Extravascular - outside (within the RES macrophages in spleen. Liver, bone marrow)

Question 21

Describe AUTOIMMUNE HAEMOLYTIC ANAEMIA

Answer 21

• Autoantibodies (ie Immunoglobulin -Ig – protein produced by own B lymphocytes) bind to the red cell membrane proteins
• Cells in the RES recognise part of the antibody, attach to it and remove it and the red cell from the circulation

Question 22

Describe Myelofibrosis

Answer 22

• Rare haemotological condtiion
• Bone marrow gets very fibrotic - increase in reticulin/ collagen fibers
• No more space for cells to go so there is less room for haemopoesis to happen
• Reduced erythropoesis
• Increased removal RES – spleen gets bigger starts removing cells
• Patients become anaemia and have a low platelet count

Question 23

How do we evaluate anaemia ?

Answer 23

• Mechanism
• Size
• Reticulocytosis

Question 24

When do we get Anaemia with reticulocytosis?

Answer 24

1. Acute blood loss
2. Splenic sequestration - of cells in spleen > enlarged spleen
3. Haemolysis

Question 25

Define some ways in which haemolysis arises which causes anaemia with reticulocytosis?

Answer 25

1. Non-Immune 2. Mechanical - Heart valves/ Microangiopathic haeamolytic anaemia (MAHA 3. Haemoglobinopathies 4. Enzyme defects 5. Membrane defects

Question 26

Define the 3 classes of Anaemia

Answer 26

Question 27

Identify some causes of primary bone marrow failure

Answer 27

* Aplastic anaemia * Red cell aplasia

Question 28

Identify soem causes of secondary bone marrow failure

Answer 28

Anaemia of chronic disease Combined haematinic deficiencies Uraemia Endocrine abnormalities HIV infection

Question 29

What type of anaemia does Vitamin B12 / folate deficiency cause and descibe this?

Answer 29

* **Megaloblastic anaemia -** Commonest cause of macrocytic anaemia * Deficiency in building blocked required for DNA synthesis * Characterised by **asynchromonous nucleur maturation** - cell division lag behind cytoplasm development, Large (“mega”) red cell precursors are released into the bloodstream with inappropriately large nuclei and open chromatin

Question 30

Describe the pathway of vitamin B12 absorption

Answer 30

•B12 binds to **haptocorrin** (secreted by salivary glands) --\> B12 and haptocorrin molecules enter the stomach - Stomach has **parietal cells** (HCl production) (also produce **intrinsic factor** - produced in stomach and also passes into the small intestine) ​ * **Haptocorrin B12** factor splits apart and B12 binds to the **intrinsic factor ​** * B12 intrinsic factor complex passes down to the **terminal ilium​** * In terminal ilium – B12 is absorbed across the terminal ilium ​ * Enters the **portal blood** attached to carrier portien called **transcobalamin** ​ * Mainly **stored in the liver** and carried to areas that it is required – e.g. erythroid cells and nerve cells ​

Question 31

What is **pernicious anaemia?**

Answer 31

Lack of **intrinsic factor** in Vitamin B12 absorption

Question 32

What is folate and what does it do?

Answer 32

Folate * Present in most foods, yeast, liver and leafy greens * Absorption in the duodenum and jejunum Function * Stable form: Methyl-THF * Dietary folates: converted to tetrohydrofolate **‘functional form’** – carbon donator, moves carbon around from diff. molecules **•THF (functional folate)** essential for: **thymidylate synthesis** (synthesis of Thymine) - needed for **DNA synthesis** **​**

Question 33

What is the role of vitamin B12

Answer 33

* Important for producing the **building blocks for DNA synthesis** (via **thymidine synthesis**) * Produces the **functional form of Folate** - tetrahydrofolate * **Vitamin B12 transfers a methyl group** from FH4 to homocysteine to form methionine - to form functional THF

Question 34

What happens if there is a lack of Vitamin B12

Answer 34

* Lack of B12 means that the methyl group cannot be moved - so we get methyl THF instead of THF * This traps’ folate in the stable methyl- FH4 form * Results in impaired thymidine synthesis

Question 35

How do a lack of Vitamin B12 and Folate cause megaloblastic anaemia?

Answer 35

* Leads to **thythymidylate deficiency** * No thymine, **uracil** is incorporated into **DNA** instead **•DNA repair enzymes** detect error and **DNA strands destroyed** •Causes **asynchronous maturation** between **nucleus** and the **cytoplasm** **•Nucleus (lacking DNA)** not fully mature •But **cytoplasm**, in which RNA production and haemoglobin synthesis **continues matures at the normal rate**

Question 36

How do cells appear on a peripheral blood film when they show megaloblastic features

Answer 36

* **Macrocytic** red cells * **Anisopoikilocytosis (**RBCs that are of different sizes and shapes) with **tear drops** * **Hypersegmented** neutrophils * Can see **white cell precursors** also **megaloblastic** anaemia **•Nucleus (lacking DNA)** not fully mature

Question 37

How do we investigate megaloblastic anaemia?

Answer 37

* Low **Hb** * High **MCV** (only 75%) * Blood film shows **‘megaloblastic’ features** – large, hypersegmented neutrophils * High **bilirubin** and **LDH** (indicates **cell turnover)** * Check **B12** and serum **folate** at the same time - * Vit B12 test is a **poor** test (also if borderline, **repeat** } If indeterminate * Check plasma total **homocysteine** (tHcy) and/or plasma methylmalonic acid (MMA) (intermediates in pathway

Question 38

How do we treat Vit B12 and Folate deficiency

Answer 38

Folate deficiency - **oral folic acid** recommended to pregnant women Vitamin B12 * Depends on the course * **Pernicious** anaemia – **hydoxycobalamine** * **Instramuscular** B12 not oral because they cant absorb it