Anaemia Vit B12 And Folate Metabolism And Megaloblastic Anaemia Flashcards
What is anaemia?
Haemoglobin outside of the reference range for the normal
population
Haemoglobin carries oxygen
Symptoms: shortness of breath, tiredness, cardiac failure,
palpitations, headache
Signs: pallor, tachycardia, tachypnoea, hypotension
Other signs and symptoms specifically associated with
the cause of anaemia
What are specific signs of anaemia?
Iron deficiency
- koilonychia
- oesophageal webs
- angular stomatitis
Vit b12 deficiency
- glossitis
Thalassaemia
-abnormal facial bone development
What is the life of a red blood cell
Erythoropiesis and Hb synthesis in bone marrow
Cytoplasm goes blue to pink as it becomes more haemoglobinised
Peripheral RBCs circulate for ~120 days
Reticulo endothelial system removes RBCs - if not working properly the red cells not last the w120 days?
Why might anaemia develop?
Bone marrow
- reduced erythropoiesis
- dyserythropoiesis
- haemoglobin synthesis
Peripheral red blood cells
- structure (membrane) problems
- metabolism
-loss of red cells
Removal
- RE ssystem problems
Why might there be reduced erythropoiesis?
Lack of response to the haemostatic loop – eg in chronic kidney disease the kidney stops making EPO
- Empty bone marrow unable to respond to stimulus from EPO eg after chemotherapy or toxic insult such as parvovirus infection or in aplastic anaemia normal haemopoietic cells are reduced
- Marrow infiltrated by cancer cells or fibrous tissue (myelofibrosis) means the normal haemopoietic cells are reduced
Can be reduced for a number of reasons
Driven by erythropoeitin produced by kidney - low o2 levels
Stimulated bone marrow to produce more red dells
O2 levels increase
Chronic renal failure = anaemia
If bone marrow empty - wot produce enough
If by is infiltrated - may not be enough space for red cells to grow
What is dyserythropoiesis?
• Anaemia of Inflammation or anaemia of Chronic Disease
• 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
Cytokines lead to difficulty in released iron from macrophages so red cells don’t have enough
Myelodysplastic syndromes (MDS)
• Production of abnormal clones of marrow stem cells
Primary bone marrow disorders
Abnormal red cells - not allowed out into circulation
What are defects in Hb synthesis?
Deficiencies in essentials
Lack of iron: deficiency in Haem synthesis
◦ Iron deficiency
◦ Anaemia of chronic disease (functional lack of iron)
Lack of B12/folate: Deficiency in the building blocks for
DNA synthesis
◦ Megaloblastic anaemia Mutations in the proteins encoding the globin chains
◦ Thalassaemia
◦ Sickle cell disease
What are inherited defects in red cell membrane structure
Aren’t many structures in mature red cells - empty membrane - cytoplasm w/ Hb
Genetic changes in genes which code proteins for rbc memb which leads to structureal changes leading them to be taken out early
Hereditary spherocytosis - round
Hereditary eliptocytosis - eliptoid
Hereditary pyropoikilocytosis - change in shape and size, get stuck, some look abnormal and get taken out by reticuloendothelial system too quickly
Haemolytic anaemia
The cells are less legible and are damages more easily and break up or are removed more quickly from the circulation
What are acquired defects in red cell membrane structure
◦ Mechanical damage to red cells - cells taken out of circulation or break down in circulation
Heart valves - shared as they go through
Vasculitis
MAHA (microangiopathies) - blood clots form in small vessels - sheared ad they go through the clots
DIC – disseminated intravascular
coagulopathy
◦ Heat damage
Burns
◦ Osmotic change
Drowning
Do red cells make ATP?
Red cels make a bit of ATP to keep membrane working properly, 2 main pathways
Defects in these pathways can lead to problems in redox in he cells, abnormal oxidised problem leading to cells being taken out of circulation too quickly and lipid bilayer not being maintained properly
What are defects in red cel metabolism
Red cell enzyme defects can lead to anaemia
Best recognised are:
◦ Glucose-6-phosphate dehydrogenase
◦ Pyruvate kinase deficiency
How are excess red cells removed
The spleen removes damaged or defective red cells
In some conditions there’d cells dont look right
Cells in spleen and liver take them out and break them down
Excess of abnormal cels - taken out very quickly
It will do this in many of the causes of anaemia already covered eg membrane disorders, enzyme disorders, haemoglobin disorders
In Haemolytic anaemias (Session 5) red cells are destroyed more quickly as they are abnormal or damaged
This can occur within the blood vessels intravascular or outside
(within the RES macrophages in spleen. Liver, bone marrow)
extravascular
What is autoimmune haemolytic anaemia
In this condition 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
Ab binds to red cells
Liver/spleen recognise this as abnormal
Removr rbc
Autoimmune
What is myelofibrosis?
Fibrotic marrow with little space for haemopoiesis Blood film shows red cells looking like tear drops
What is thalassaemia?
Hawmoglobinopathy Mutation in genes that code for globin chains Hb nabnormal Rbcs abnormal Cells removed very quickly Defect in Hb synthesis Body not able to make enough good red ells RE system problem
Erythropoiesis – expansion into other sites causes growth of liver and spleen, bone and sinus expansion
What are reticulocytes and how can they indicate bone marrow function?
Rtculocytes = early red cells - released early if patient is anaemia and bm funioning normaly
Release of reticulocytes - polychromatic - more colour than the other red cells - blue bc they have a bit more RNA left in them - if RNA degrades they become pink in colour
Reticuloctes there tell us that bone marrow is working
Anaemia ppl with working bone marrow have high reticulocytes count - if thy dont smth is wrong in bone marrow thats preventing them from being release
What if an anaemia person with an appropriate reticulocytes response shows evidence of haemolysis?
Yes - work out the cause
No - look for evidence of bleeding
What if an anaemic person does not have an appropriate reticulocytes response?
Check rbc indices
Microcytic: <80fl
Macrocytic:>100fl
Normocytic
What is anaemia with reticulocytosis?
Acute blood loss Splenic sequestration Haemolysis ◦ Immune mediated eg autoimmune or drug related ◦ Non-Immune Mechanical Heart valves Microangiopathic haeamolytic anaemia (MAHA) Haemoglobinopathies Enzyme defects Membrane defects
Exclude haemolysis - biochemical tests to haelpeveidence of haemolysis - look for cause
If not most common cause is bleeding
What is anaemia with low reticulocytes count?
Low MCV (Microcytic) ◦ Thalassaemia trait ◦ Anaemia of chronic disease (may be normocytic) ◦ Iron deficiency ◦ Lead poisoning ◦ Sideroblastic anaemia
High MCV (Macrocytic)
- Vitamin B12 deficiency
- Folate deficiency
- Myelodysplasia
- Liver disease
- Hypothyroidism
- Alcohol
Normal MCV (Normocytic) ◦ Primary bone marrow failure - very rare - Aplastic anaemia - Red cell aplasia ◦ Secondary bone marrow failure - Anaemia of chronic disease - Combined haematinic deficiencies - Uraemia - Endocrine abnormalities - HIV infection
Explain vitamin b12 absorption
Vitamin B12 is synthesised by microorganisms; humans acquire B12 by eating foods of animal origin, leading to a large excess of B12 in the diet of meat eaters
B12 binds haptocorrin secreted by salivary glands and the complex passes through the stomach
In the small intestine, Vit B12 is released from haptocorrin and binds the glycoprotein intrinsic factor (IF) produced by parietal cells stomach in the , leading
IF-B12 complex then binds to receptors in the terminal ileum
to absorption of B12 and destruction of IF
In the portal blood Vit B12 binds the plasma protein transcobalamin II which delivers B12 to the bone marrow and other tissues
What are causes of low vit b12
Dietary deficiency
Vegan diet; poor diet
Lack of intrinsic factor (IF)=Pernicious anaemia
An autoimmune disease affecting gastric parietal cells causing lack of intrinsic factor; gastrectomy
Disease of the ileum
Crohn’s disease; ileal resection; tropical sprue
Lack of Transcobalamin
Congenital deficiency
What is folate
Folate present in most foods, yeast, liver and leafy greens especially rich source
5mg stores for abut 3-4 months
Absorption occurs in the duodenum and jejunum
Only several months worth
Use of folate increases eg if pregnant or if have haemolytic anaemia - using forte more quickly - stores run down - folate deficient
What could deficiency of folate result from?
Dietary deficiency:
poor diet
Increased use:
pregnancy, increased erythropoiesis eg haemolytic anaemia,
severe skin disease (e.g psoriasis, exfoliative dermatitis)
Disease of the duodenum and jejunum:
proximal small bowel disease eg coeliac disease, Crohn’s disease
Lack of methylTHF
drugs which inhibit dihydrofolate reductase enzyme (eg Methotrexate)
Others: alcoholism (multifactorial); urinary loss of folate in liver disease and heart failure; other drugs eg anticonvulsants
How do vit b12 and folate deficiency cause a megaloblastic anaemia?
Dietary folates are all converted to methyltetrahydrofolate methylTHF which is the ‘functional form’
methylTHF is essential for: serine-glycine conversion, histidine
catabolism, purine synthesis, and most importantly, thymidylate
synthesis which is needed throughout the body for DNA synthesis
Vitamin B12 function is to:
◦ transfer a methyl group from L-methylmalonyl-CoA to form
Succinyl-CoA
◦ transfers of a methyl group from FH4 to homocysteine to form
methionine
◦ Lack of B12 ‘traps’ folate in the stable methyl- FH4 form causing a ‘functional’ folate deficiency
So….both folate and Vit B12 deficiency ultimately lead to thymidylate deficiency
In the absence of thymine, uracil is incorporated into DNA instead
DNA repair enzymes detect the error and DNA strands are
destroyed
This causes asynchronous maturation between the nucleus and
the cytoplasm.
◦ The nucleus (lacking DNA) does not fully mature,
◦ The cytoplasm ,in which RNA production and haemoglobin synthesis continues, matures at the normal rate
What is megaloblastic anaemia?
Both B12 and folate necessary for nuclear divisions and nuclear maturation. When deficient, nuclear maturation and cell divisions lag behind cytoplasm development. This leads to large red cell precursors with inappropriately large nuclei and open chromatin. The mature red cells are also large leading to a macrocytic anaemia
What can be seen on the peripheral blood film for megaloblastic anaemia?
The peripheral blood film shows megaloblastic features:
• macrocytic red cells
• anisopoikilocytosis with tear drops
• hypersegmented neutrophils
• Can see white cell precursors also
As deficiency progresses a pancytopenia can develop ie low platelets and neutrophils too
How can deficieny in vit b12 or folate cause neurological disease?
Vitamin B12 (not folate) deficiency is also associated with neurological disease – focal demyelination affecting the spinal cord, peripheral nerves and optic nerves.
Folate deficiency in pregnancy can cause neural tube defects
How can megaloblastic anaemia be investigated?
Low Hb
High MCV (only 75%)
Blood film shows ‘megaloblastic’ features
High bilirubin and LDH - due to increased cell descrcution and production
Check B12 and serum folate at the same time
Vit B12 test is a poor test so if borderline, repeat - looking for pictograms amounts
If indeterminate
◦ Check plasma total homocysteine (tHcy) and/or
◦ plasma methylmalonic acid (MMA)
Check for anti-Intrinsic Factor antibodies
◦ if no evidence of food malabsorption or other
25% of ppl with vit b12/folate deficiency have normal sized rbcs
How are vit b12 and folate deficiency treated?
Folate
◦ Oral folic acid
Vit B12
◦ Pernicious anaemia: Hydroxycobalamine (intramuscular) for life
◦ Beware hypokalaemia (low potassium)
◦ Other cause: oral cyanocobalamine
Need to know if lack of absorption or lack of intake
Lack of absorption - giving oral b12 wont help
Recommended that pregnant ppl have folic acid - reduce incidence of neural tube defects
Vit b12 depends on cause - vegan, gastrectomy, chrons egc
Pernicious - not oral
Transfusion in patients with Vit B12 deficiency
◦ High output cardiac failure
If parameters don’t improve somehting going wrong
Body adapts to being anaemia eg heart harder and faster - hypertrophy - cardiomyopathy
Occurs over years not acute
Heart has to adapt
Won’t feel unwell bc used to it
Must transfuse with caution
Give b12 and wait for response
Give maybe 1 unit
Can be precipitated into cardiac failure
