CLASSIFICATION OF ANAEMIA:Macrocytic Anaemia

Lazarela Vucinic 2009

Macrocytic anaemias

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Macrocytic anaemia(MCV>RR)

Megaloblasticanaemia

Non-megaloblasticanaemia

- B12 deficiency- Pernicious anaemia

- Folate deficiency- B12/Folate

- Liver disease- Alcoholism

- MDS- Drug induced- Reticulocytosis- Others

-Oval macrocytes-Hypersegmented neutrophils

Round macrocytes

Lazarela Vucinic 20093

Vitamin B12 (Cobalamin)

• Synthesized by some microorganisms• Food that contains cobalamin is from animal

origin • Average daily diet contains ~ 5-30ug– 1-5ug is absorbed

• ~2-5mg are stored– Liver– Kidneys

B12 absorption

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www.uq.edu.au/vdu/HDUAnaemiaMegaloblastic.htm

Accessed 14.04.08

Mouth:Unbound B12 may be absorbed

Stomach:

Protein-bound B12 detaches R-Protein picks up B12 IF secreted

Upper small intestine:

R-protein releases B12. IF picks up B12

Lower small intestine:

IF-B12 attaches to receptor Some unbound B12 absorbed

Intestinal cells: B12 attaches to transcobalamin II

http://www.veganhealth.org/b12/images/b12absorption1.gif Accessed 14.04.08

Blood:

Transcobalamin II carries B12 to cells OR to liver for storage (transcobalamin III)

Liver:

B12 is stored and released into small intestine via the bile

Transcobalamins• Transcobalamin II

– Synthesised by the liver, vascular endothelium, enterocytes, macrophages and fibroblast

– Half – life ~ 90min– Mainly circulates as apoTCII– Carries 6-25% of B12 & takes it to the tissues– Binds to TC II-R and is internalised by receptor-mediated endocytosis & is not recycled

• Transcobalamin I and III (TCI & TCIII)– Synthesised in the liver– 75% of plasma B12 binds to TCI

• Storage protein for B12

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B12 function

http://emedicine.medscape.com/article/1152670-overview Accessed180309

B12 function

7http://emedicine.medscape.com/article/1152670-media Accessed 140309

Lazarela Vucinic 2009

B12 deficiency• Folate trapping– Abnormal DNA synthesis

• Homocysteine– Plasma toxicity– Deterioration of inner lining of arteries and veins– => leads to risk for CHD, PVD and stroke

• ? of S-adenosylmethionine (SAM)– Shown to help treat depression– ?Abnormal neuronal conduction

• Leads to development of methylmalonic aciduria– Associated with neurological symptoms and learning

deficiencies

Causes of B12 deficiency

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B12 deficiency

Inadequate intake

Increased need

Impaired absorption

Lack of IF Failure to separate from haptocorrin

Malabsorption

Competition for B12

Gastrectomy

Perniciousanaemia

Pernicious anaemia

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Mean age of onset is 60 years Impaired absorption of B12 due to a lack

of IF Autoimmune disorder

? genetic predisposition Lymphocyte mediated destruction of

parietal cells => IF not secreted Antibodies block IF action

Blocking Abs detectable in serum Leads to development of atrophic gastritis

Folate• Normal daily intake = 650 μg• Amount lost = 13 μg (urine)• Daily requirements = 200 μg• Storage = 5mg• Food sources include green leafy vegetables , bananas, strawberries,

nuts, liver, yeast• Lots of food has been fortified with folate• Vulnerable to heat and dissolves in water - so cooking can reduce the

levels

Research indicates that increased folate intake can preventseven out of 10 births of babies affected by a neural tube defect

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Folate• Before folate can be used, the following

reactions occur:

• Occurs as conjugate of one or multiple glutamic acids– Folic monoglutamates & polyglutamates exist

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FolateDihydrofolate

FH2

TetrahydrofolateFH4

Dihydrofolate reductase

Folate absorption

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1. Unconjugatedor conjugated dietary folate

2. All polyglutamates

are deconjugated

3. Monoglutamatestransported across

intestinal epithelium

4. FH4 formation inintestinal epithelium

5. Monoglutamatescirculate in blood& are transported

into cells

6. Polyglutamatesformation inside cells

Folate function

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http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1519435&blobtype=pdf Accessed 150408

The principal function of folate coenzymes is to accept or donate one-carbon units in key metabolic pathways

Folate-requiring reactions include: those involved in

phases of amino acid metabolism

purine and pyrimidine synthesis

formation of the primary methylating agent, S-adenosylmethionine (SAM)

Causes of folate deficiency

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Increased need

Excessive loss

Folatedeficiency

Impaired absorption

Inadequate intake

Impaired utilisation

Symptoms of B12 & folate deficiency

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Anaemia Weakness Fatigue SOB Pallor – may be severe

Loss of epithelium Glossitis Gastritis Constipation

Neurologic symptoms May appear before

anaemia Memory loss Loss of balance Numbness in toes and

fingers Depression “Megaloblastic madness”

Jaundice Weight loss

Megaloblastic anaemia

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FBE Results: Hb/RCC/Hct MCV RDW Plt/WCC

=>Pancytopenia may develop Oval macrocytes Hypersegmented neutrophils No polychromasia Poikilocytosis, tear drops In severe megaloblastic anaemia

Basophilic stippling Howell Jolly bodies

Lazarela Vucinic 2009

Megaloblastic anaemia

Lazarela Vucinic 2009

Megaloblastic anaemia

Bone Marrow• Shows megaloblastic changes• Nuclear-cytoplasmic asynchrony• Hypercellular • M:E = 1:1– Intramedullary haemolysis due to ineffective erythropoiesis

• Giant WBC precursors– Metamyelocytes and bands

• Megakaryocytes varyIs NOT performed unless there is a suspicion of megaloblastic

anaemia in a child

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Diagnosis of B12/Folate deficiency

• Bilirubin• LDH• Haptoglobin• Homocystine• IF of parietal cell antibodies• ? Methylmalonic acid – serum or urine

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Evidence of haemolysis

Treatment of megaloblastic anaemia• Directed at specific vitamin deficiency– Treating B12 deficient patient with folate may increase

neurological symptoms

• Folate and B12 tablets administered orally– Iron may be supplemented

• B12 may be administered intramuscularly– No need for IF– Lifelong administration for PA patients

• Sublingual or nasal B12 available – Expensive

Liver disease• Anaemia

– Macrocytes (round) & target cells• Due to abnormalities of RBC membrane lipids

– anisocytosis & poikilocytosis than in megaloblastic anaemia– reticulocytes

• Thrombocytopenia– Often mild and due to hypersplenism– If due to alcohol

• May have abnormal platelet aggregation and secretion• Direct marrow suppression

• Coagulopathy– Lack or malabsorption of VitK– Decreased synthesis of coagulation proteins– Synthesis of abnormal proteins

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Alcoholic liver disease• The effects of alcohol may be:

– Direct – seen in the BM– Indirect – liver disease or due to nutritional abnormalities

• Anaemia (? haemolytic) + impaired RC production• Leucopenia + neutropenia

– Suppression of growth factors – Splenomegaly

• Concurrent infection/inflammation that may give rise to ACD– Abnormal N function and decrease Ab production

• Thrombocytopenia– Ineffective thrombopoiesis

• May lead to development of (reversible) sideroblastic anaemia• Folate and iron deficiencies are common

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Lazarela Vucinic 2009

Liver disease

Diagnosis of liver disease

• Abnormal LFT• Coagulation– PT

• Prolonged even in mild liver disease • fVII and fX particularly affected

– APTT– Fibrinogen

• May be elevated in early liver disease (acute phase reactant)• May be structurally abnormal

– Folate and Iron storage may be low

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Lazarela Vucinic 2009

Learning objectives

• Be able to describe different types of macrocytic anaemias and their causes

• Understand the function and metabolism of B12 and folate and the causes and impact of deficiency in either one

• Show an understanding of tests and expected results that may be performed in order to diagnose B12/Folate deficiency

• Be able to explain other causes of macrocytosis (liver disease, MDS and drug induced)

Lazarela Vucinic 2009

Study Questions• What are the expected results in a patient

with megaloblastic anaemia and why?• Why do we need B12 and Folate and what

effect will the deficiency of either one have?• What is pernicious anaemia, what is its cause

and how is it diagnosed?• How would you diagnose liver disease?• List the causes of macrocytosis and briefly

explain the pathophysiology of each.

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