Macrocytosis & Macrocytic Anaemia

Question 1

Define macrocytosis vs macrocytic anaemia

Answer 1

Macrocytosis - Larger than normal volume RBCs
Macrocytic anaemia - Anaemia in which the RBCs are larger than normal volume

Question 2

How would you recognise macrocytes on blood film

Answer 2

Normal RBC is the same size as a lymphocyte nucleus.
Macrocyte is larger than a lymphocyte nucleus

Question 3

Macrocytosis aetiology

Answer 3

Megaloblastic macrocytosis
- B12 deficiency (associated with anaemia)
- Folate deficiency (associated with anaemia)
- Certain drugs

Non- megaloblastic macrocytosis
- Alcohol
- Liver disease
- Hypothyroidism
- Marrow failure (associated with anaemia)

False macrocytosis (false test result)
- Reticulocytosis
- Cold Agglutinin

Physiological
- Pregnancy
- Neonates

Question 4

Megaloblastic vs nonmegaloblastic (macrocytic) anaemia

Answer 4

Megaloblast - Red cell precursor that is larger than normal and has an immature nucleus due to a defect in DNA synthesis, nuclear maturation & cell division

Megaloblastic macrocyte - Macrocyte than originated from a megaloblast

Non-megaloblastic - Macrocyte than did not originate from a megaloblast

Question 5

Normoblast -> Reticulocyte -> Mature erythrocyte. Describe this transition/ pathway.

Answer 5

A normoblast is a RBC precursor with a nucleus and is mainly marrow based.

As normoblasts develop…
- they accumulate Hb in their cytoplasm
- their cell size decreases/ divides
- their nuclear size decreases/ divides (matures)

Accumulation of Hb in the norm last triggers them to stop dividing and lose their nucleus.

This forms a reticulocyte (immature RBC) than moves into the blood stream.

A reticulocyte is larger than a mature RBC and has RNA making it polychromatic/purple-ish in colour.

A reticulocyte matures in the bloodstream, losing its RNA and decreasing in size, to form a mature RBC.

Question 6

Megaloblastic anaemia aetiology

Answer 6

Defect in DNA synthesis & cell division of RBC precursors,
Usually due to a B12 &/ folate deficiency

Question 7

Megaloblastic anaemia pathophysiology

Answer 7

1) Defect in DNA synthesis and nuclear maturation in normoblast (RBC precursor) =>

2) Reduced cell division => bigger, immature nuceli (megaloblast), increased apoptosis => decreased number of cells

3) The Hb levels accumulate normally and trigger enucleation and halt cell division =>

4) This leaves behind a larger-than-normal RBC (macrocyte) and decreased number of RBCs (anaemia)

Question 8

State the key roles of B12 and folate

Answer 8

B12 & folate are required for thymine synthesis
=> affect DNA synthesis & nuclear maturation

B12 & folate are required for methionine synthesis
=> affect DNA modification & gene activity

B12 also plays a role in lipid synthesis & myelin production
=> neurological effects

Question 9

Describe B12 absorption & transport

Answer 9

B12 travels down the oesophagus and through the stomach with salivary enzyme HC

Change in pH (gastric -> pancreatic secretions) and presence of tripsin (pancreatic secretions) in small bowel cause:
- B12 to dissociate from HC
- B12 to bind to intrinsic factor

B12 is then absorbed in the distal small bowel (IF is excreted)

B12 is then transported from enterocytes to bone marrow etc by transcobalamin II

Question 10

Referring to B12 absorption, list causes of B12 deficiency

Answer 10

Decreased dietary intake
- vegans/ vegetarians

Decreased stomach acid
- Atrophic gastritis
- PPIs/ H2 receptor antagonists
- Gastrectomy/ bypass

Loss of intrinsic factor
- Pernicious anaemia

Decreased pancreatic tripsin secretion
- Chronic pancreatitis

Decreased absorption in the small bowel
- bacterial overgrowth
- Crohn’s, terminal ileum resection

Question 11

Folate deficiency causes

Answer 11

• Inadequate dietary intake (esp since less folate stores)
• Malabsoprtion (coeliac, Crohn’s)
• Excess use (Haemolysis, exfoliating dermatitis, pregnancy, malignancy)
• Drugs (anticonvulsants)

Question 12

What foods contain B12 vs folate? Where is B12 vs Folate absorbed? Which has more body stores?

Answer 12

B12 - animal food
Folate - liver, leafy veg, fortified cereals

B12 - Terminal ileum
Folate - Jejunum (& some duodenum)

B12 - 4 yrs
Folate - 4 months (& so more likely to be dietary)

Question 13

B12 &/ Folate deficiency clinical presentation

Answer 13

• S&S of anaemia
• Weight loss, diarrhoea
• Infertility
• Smooth, beefy coloured, sore tongue
• Jaundice
• Developmental symptoms
• Neuropsychiatric symptoms (B12)

Question 14

What clinical features occur with B12 but not folate deficiency

Answer 14

Neuropsychiatric symptoms - neuropathy, dementia etc
(Some symptoms are irreversible - important early recognition)

Question 15

Why can B12/Folate deficiency (megaloblastic microcytic anaemia) cause jaundice

Answer 15

=> Ineffective erythropoiesis
=> RBCs die prematurely in the marrow
=> Hb & LDH released
=> Hb converted to bilirubin

I.e. Intra medullary haemolysis

Question 16

What laboratory test would be used when diagnosing B12/folate deficiency? Describe the FBC & blood film findings in B12/folate deficiency

Answer 16

• FBC
  (Macrocytic anaemia & possible pancytopenia)
• Blood film
  (Macrovalocytes and ‘hypersegmented’ nuclei neutrophils)
• B12 & folate serum levels
• Auto-antibodies check
  (anti-IF is specific not sensitive)
  (Anti-GPC is sensitive not specific)

Question 17

Megaloblastic anaemia/B12 or folate deficiency management

Answer 17

Treat the cause e.g.
- dietary cause? => dietary advice & supplements
- pernicious anaemia? => IM Vit B12
- PPIs/H2 RA => medication review

Life threatening anaemia?
=> RBC transfusion

Question 18

What is pernicious anaemia

Answer 18

Autoimmune condition which results in destruction of gastric parietal cells and production of antibodies against intrinsic factor.

Results in intrinsic factor deficiency with B12 malabsorption & deficiency

Question 19

What conditions are associated with pernicious anaemia

Answer 19

• Atrophic gastritis
• Autoimmune e.g. hypothyroidism, Addison’s, vitiligo

Question 20

Pernicious anaemia treatment

Answer 20

IM B12 (bypass absorption)

Question 21

Non-megaloblastic anaemia aetiology

Answer 21

• Alcohol (not always associated with anaemia)
• Liver disease (not always associated with anaemia)
• Hypothyroidism (not always associated with anaemia)
• Marrow failure

Question 22

False macrocytosis aetiology

Answer 22

(volume of the mature red cell is normal, but the MCV is measured as high)

• Reticulocytosis
• Agglutination of RBCs e.g. due to cancer signals

Question 23

Physiological causes of B12 deficiency

Answer 23

Oral contraceptive pill
Pregnancy

Question 24

What cell produces Intrinsic Factor (IF)

Answer 24

Parietal cells in the stomach

Question 25

What is cobalamin

Answer 25

A form of B12
Is the main dietary source of B12
Is mainly found in animal products/ meat

Question 26

What protein transports B12 (cobalamin) in the blood

Answer 26

Transcobalamin II

Question 27

Describe a diagnostic method to determining the cause of a macrocytic anaemia

Answer 27

Reticulocyte count?
- Raised? => Haemorrhage or haemolysis
- Normal/Decreased? => Test blood film

Blood film shows hyperseg. neutrophils & macroovalocytes?
- Yes? => Check Serum B12 &/ folate levels
- No? => Non-megaloblastic anaemias (liver disease, hypothyroidism, alcoholism, marrow failure)

B12 &/ folate levels
- low-normal? => megaloblastic anaemia => check for cause e.g. antibodies for PA
- normal-high? => check for marrow failure causes of non-megaloblastic anaemia

Question 28

When testing for pernicious anaemia, what antibodies are specific and which are sensitive

Answer 28

Parietal cell antibodies - Sensitive (not specific)
Intrinsic factor antibodies - Specific (not sensitive)