Megaloblastic Anaemia Flashcards
What exactly is megaloblastic anaemia?
Production of fewer but larger red blood cells, thus a decreased ability to carry O2
MCV > 98 fL
How many people have macrocytic anaemia
Between 2.5-4% of people
What percentage of people with macrocytosis actually have anaemia?
up to 60% of people
What might macrocytosis without anaemia indicate
Early folate/vitamin B12 deficiency
What might cause macrocytic anaemia
(10)
Alcoholism
Folate/Vitamin B12 deficiency
Drugs - chemo drugs
Reticulocytosis due to haemolysis or bleeding
Myelodysplasia,
Liver disease
Hypothyroidism
Haemorrhage
COPD
Splenectomy
What other than macrocytes might be seen in megaloblastic anaemia?
Hyper-segmented lobed nueutrophils
How can you tell the difference between megaloblastic anaemia and nonmegaloblastic anamia
Megaloblastic anaemia -> oval shaped (macroovalocytes) and hypersegmented neutrophils
Nonmegaloblastic haemolytic anaemia with polychromatophilic round macrocytes and normally segmented neutrophils. Schistocytes also present.
What are some clinical features of megaloblastic anaemia
Insidious onset with gradually progressive symptoms and signs of anaemia (pale and low haemoglobin)
Many asymptomatic patients are diagnosed when FBC is performed for another reason and reveals macrocytosis
Cracking at side of the mouth common
How is megaloblastic anaemia classified?
As a nuclear maturation defect
What are megaloblasts and how do they form?
(4)
Large blasts
Early megaloblast -> intermediate megaloblast -> late megaloblast -> macrocyte
Defect in DNA synthesis retards proliferation and maturation of all haemopoietic cells
Bone marrow is hypercellular
What happens in sever megaloblastic anaemia?
pancyopenia
What are the lab results of megaloblastic anaemia?
(3)
MCV up
MCH up
MCHC Normal or low
Comment on the bone marrow in megaloblastic anaemia
(5)
Most characteristic finding is dissociation between nuclear and cytoplasmic development in the erythroblasts
The erythroblast nucleus maintains a primitive appearance despite maturation and haemoglobinisation of the cytoplasm
fully haemoglobinised (orthochromatic) erythroblasts, which retain nuclei, are seen
Giant and abnormally shaped metamyelocytes and enlarged hyperpolypoid megakaryocytes are characteristic
Many of these abnormal immature cells die in BM resulting in ineffective erythropoiesis
List some clinical consequences of vitamin B12 deficiency
(5)
Metabolic pathways reliant on Vitamin B12 are widely distributed so there are many pathological conditions associated with deficiency
Any or all of these pathologies may arise in Vitamin B12 deficiency
Haematological: Megaloblastic Anaemia
Neurological: Due to demyelination include peripheral neuropathy, ataxia, loss of sensation
Psychological: Depression, psychosis, memory loss, confusion or irritability
Write about Vitamin B12 and folate metabolism
(7)
Vitamin B12 (Cyanocobalamin) is required as a co-factor for a number of essential metabolic pathways
Co-factor in the formation of succinyl-CoA
Succinyl CoA is required at early stage of haem synthesis
Co-factor along with folate to convert homocysteine to methionine
Methionine is required for myelin synthesis
As a cofactor to convert folate (methyl tetrahydrofolate) into tetrahydrofolate
Tetrahydrofolate is required for DNA synthesis
What is Vitamin B12 called?
Cyanocobalamin
What is Vitamin B12 a co-factor in?
Formation of Succinyl CoA
Co-factor along with folate to convert homocysteine to methionine
Co-factor to convert folate (methyl tetrahydrofolate) into tetrahydrofolate
What is Succinyl Co A needed for?
Required at early stage of haem synthesis
What does methionine do
Required for myelin synthesis
What is tetrahydrate required for?
DNA synthesis
What are the two key biochemical reactions involving vitamin B12
Methionine synthesis
To assist as deoxyadenosylcobalamin in the conversion of methylmalonyl CoA to succinyl CoA
How can vitamin B12 deficiency affect the nerves
Can result in varying degrees of neuropathy or nerve damage
What is pernicious anaemia
Autoimmune condition whereby you can’t absorb vitamin B12
Write about vitamin B12
(6)
Synthesised in nature by micro-organisms
Largest of all vitamins and is water soluble
Wester diets contain between 5 and 30ug/day
Small group of compounds collectively known as the Cobalamins
Found in foods of animal origin such as liver, meat, fish and dairy produce but does not occur in fruit, cereals or vegetables
Animals acquire it by eating food of animal origin
Describe the structure of vitamin B12
Cobalt in the centre of a corrin ring which is attached to a nucleotide portion
What are the different phases to vitamin B12 absorption?
(3)
Oral Phase
Gastric phase
Intestinal phase
Write about the oral phase of vitamin B12 absorption
B12 in proteins ingested
R-binders produced by salivary glands
Write about the gastric phase of B 12 absorption
(3)
R binders bind with B12 to form R-B12 complex
Gastric parietal cells secrete pepsin and intrinsic factor
Pepsin breaks down proteins to release the B12 to bind with R binders
Write about the intestinal phase of vitamin B12 absorption
(4)
Proteases released by the pancreas split R-B12 complex
Intrinsic factor + B12 => IF-B12 complex
IF-B12 binds to IF receptor on Ileal cells and is taken up into circulation
Transcobalamin transports cobalamin around the body to wherever it is needed
IF
What is intrinsic factor?
(2)
A glycoprotein that free vitamin B12 combines with
It is synthesised by the gastric parietal cells
Write about IF-Vitamin B12 complex and it’s role in absorption
(5)
One molecule of Vit B12 binds to one molecule of IF
IF-Vitamin B12 complex binds to a specific surface receptor for IF
Vitamin B12 is internalised into the mucosal cell and passed across into the plasma
Vitamin B12 requires energy for absorption
IF remains within the mucosal cell of the ileum and does not pass across the mucosa
What molecule is responsible for transporting vitamin B12
Transcobalamin
What are the different types of transcobalamin
Transcobalamin 1
Transcobalamin 2
Transcobalamin 3
What does transcobalamin 1 do?
Binds most vitamin B12 in the body
Has little capacity to transfer vitamin B12 to tissues
What does transcobalamin 3 do?
Released from the granules of neutrophils
Not involved in Vitamin B12 transport
Named incorrectly
What happens when the transcobalamin 2/B12 complex has reached its destination
Once bound to the receptor of the cell, the complex is internalised
The Vit B12 is liberated and the transcobalamin is degraded by lysosomal enzymes
What are the four categories of vitamin B12 deficiency?
Nutritional
Biologic competition
Malabsorption
Impaired utilisation
What are the three nutritional causes of vitamin B12 deficiency?
Vegans
Pregnant women on poor diet
Malnutrition
What are the three biologic competition causes of B12 deficiency
Intestinal parasite
Leishmaniasis
Bacterial overgrowth
What are the eight causes of malabsorption of vitamin B 12
Pernicious anaemia
Gastrectomy or gastric bypass
Crohn’s disease
Tropical sprue
Coeliac disease
Surgical resection of ileum
Drugs
Blind loop syndrome
What are the two causes of impaired utilisation of vitamin B12
TC II deficiency (transcobalamin deficiency)
Nitrous oxide inhalation
What is a definition of pernicious anaemia
A severe lack of intrinsic factor due to gastric atrophy
What causes pernicious anaemia
Presence of auto-immune antibodies to gastric parietal cells
Don’t really know why this happens
What does pernicious anaemia cause
(4)
Most common cause of vitamin B12 deficiency
Loss of gastric secretions including IF
It is a common disease in northern Europeans
Most common in women around 60 years of age, people with a family history of the condition and those with another autoimmune condition
Comment on the laboratory investigation of vitamin B12 deficiency
(11)
Macrocytosis
MCV > 98fL
Patient presents with anaemia usually
Blood film oval macrocytes
Hypersegmented neutrophils
Reticulocytes decreased on diagnosis, increases on treatment
WCC and Plt count reduced
Vitamin B12 assay low
IF antibodies
Hypercellular bone marrow and large erythroblasts
Plasma bilirubin and lactate dehydrogenase levels increased as a result of marrow cell breakdown
How can you tell from blood test results that there is marrow cell breakdown
Plasma bilirubin and lactate dehydrogenase levels increased as a result of marrow cell breakdown
How is pernicious anaemia treated
Vitamin B12 given as an injection directly into muscle which bypasses the need for absorption from the intestine
What is folate
The naturally-occurring form of the vitamin
What is folic acid
(3)
The synthetic form used in most supplements and fortified foods
Works the same as folic acid
Folic acid is actually better absorbed than the natural form but they have the same benefits
Give some signs of folic acid deficiency
(10)
Fatigue
Depression
Loss of appetite
Trouble concentrating
Forgetfulness
Grey hair
Poor growth
Mouth sores
Swollen tongue
Spinal cord defects e.g. spina bifida
How does folate deficiency affect pregnancy?
(5)
Added stress of rapidly growing cells in pregnancy so increased amounts of folate are required
If a woman has folate deficiency prior to pregnancy it will be intensified during gestation and may lead to premature birth and neural tube defects
Neural tube defects decreased by 36% in the US since focusing on folate supplements during pregnancy
Deficiency implicated with pregnancy loss
Restless leg syndrome also a neurological symptom of deficiency
Write about the action of folate
(3)
Levomefolic acid (5-MTHF) is required for the synthesis of methionine from homocysteine and serine to glycine
Required for the synthesis of thymidine - a purine precursor of DNA
DNA is essential for cell division
How is folate involved in cell division
(4)
Folate is needed for the synthesis of thymidine which is a precursor for thymine
Deficiency inhibits thymidolyate synthesis which is a rate limiting step of DNA synthesis, as this reaction required the coenzyme 5-MTHF
Therefore all dividing cells are affected by deficiency
i.e. deficiency results in failure to form thymine one of the purine base pair
How is folate absorbed?
(4)
Absorption occurs in upper small intestine
Polyglutamate forms are hydrolysed by pteroylpolyglutamatehydrolase (PPH) to monoglutamate form of folate in the intestine
Monoglutamate is converted to tetrahydro-folate (THF) within the small intestinal mucosa before entering the portal plasma
Transporter to liver and stored as tetrahydro-folate (THF)
What happens to polyglutamate forms of folate
Polyglutamate forms are hydrolysed by pteroylpolyglutamatehydrolase (PPH) to monoglutamate form of folate in the intestine
What happens to monoglutamate?
(2)
Monoglutamate is converted to tetrahydro-folate (THF) within the small intestinal mucosa before entering the portal plasma
Transporter to liver and stored as tetrahydro-folate (THF)
What are the five classifications of causes of folate deficiency?
Inadequate diet
Biologic competition
Increased requirement
Malabsorption
Drug inhibition
How can inadequate diet cause folate deficiency?
Low income
Elderly people with limited function/income
Alcoholics (spirits)
How can biological competition cause folate deficiency
Bacterial overgrowth in small intestine
How can malabsorption cause folate deficiency?
(4)
Ileitis
Tropical sprue
Non-tropical sprue
Blind loop syndrome
How can drug inhibition cause folate deficiency?
(4)
Oral contraceptives
Long term anticoagulant therapy
Phenobarbital
Antimetabolite chemotherapy
How can increased requirement cause folate deficiency?
Disease associated with rapid cell turnover (SCA, THal, leukaemia, pregnancy)
Write about the diagnosis of megaloblastic anaemia
(9)
Haemoglobin lower
MCV increased
WCC and platelets may be reduced
Oval macrocytes
Hypersegmented neutrophils
LDH up
BIlirubinaemia
Haptoglobin low
Reticulocyte low
What four things provide evidence of ineffective erythropoiesis
LDH up
Bilirubinaemia
Haptoglobin down
Reticulocyte count down
What clinical tests are carried out for vitamin B12 deficiency?
(4)
Diet history
Serum gastrin
IF, parietal cell antibodies
Endoscopy
What five clinical tests are carried out for folate deficiency?
Diet history
Test for intestinal malabsorption
Anti-transglutaminase and endomysial antibodies
Duodenal biopsy
Underlying disease
Comment on the folate assay
two-step assay for the quantitative determination of folate in human serum, plasma and RBCs
Write about the vitamin B12 assay
Two-step assay with an automated sample pretreatment, for determining the presence of vitamin B12 in human serum and plasma
How is vitamin B12 deficiency treated
Hydroxycobalamin -> intramuscular - 1000ug every 3 months ->
Prophylactic = total gastrectomy or ileal resection
How is folate deficiency treated
(2)
Folic acid taken orally - 5mg daily for 4 months
Prophylactic in pregnancy, sever haemolytic anaemia, dialysis, prematurity
What are the preventative measures for megaloblastic anaemia
Vegetarians/Vegans should supplement their diet especially in pregnancy or breast feeding
Gastric surgery -> should supplement with large doses of oral vitamin B12, preferably on an empty stomach
Nitrous oxide exposure inactivates vitamin B12 -> its used in anaesthesia may precipitate rapid neuropsychiatric deterioration in vitamin B12 deficient people
