7- Anaemia, Vitamin B12 & Folate

Question 1

• define anaemia, what is the key clinical point here & give general signs and symptoms.
• give some specific signs associated with specific anaemias
• give general reasons why anaemia may develop

Answer 1

• a Hb conc lower than the normal range, varies w age sex etc, anaemia itself is NOT a diagnosis, it’s a manifestation of an underlying disease so it’s important to find the cause
• (Hb carries O2 to tissues so all related to insufficient delivery of O2 to tissues) shortness of breath, headaches, angina, palpitations, pallor, tachycardia, hypotension
• koilonychia (spoon shaped nails)=iron deficiency , angular stomatitis (inflammation on corners of mouth)= iron deficiency, glossitis (inflammation & depapillation if tongue=Vit B12, abnormal facial dev (bc haemopoiesis happens in bones of face)=thalassaemia, rare in UK to get the facial def bc of screening
• life cycle of RBCs= reduced or dysfunctional erythropoiesis, abnormal haem or globin chain synthesis, RBCs in BVs= abnormal structure or mechanism, mech damage, bleeding, removal=increased rate of removal, by reticuloendothelial system

Question 2

-outline the following reasons for why anaemia might develop:
-reduced or dysfunctional erythropoeisis
-defects in Hb synthesis
-abnormal structure and mechanical damage resulting in haemolytic anaemia
-defects in red cell metabolism
-excessive bleeding
-role of the reticuloendothelial system
Anaemia is often multifactorial ie several causes. Give examples using myelofibrosis & thalassaemia.

Answer 2

• low blood O2 is sensed by pericytes in the kidney that then produce erythropoietin which binds to receptors in bone marrow and stimulates RBC production which in turn increases no of RBCs (a neg feedback loop). Anaemia can happen bc of a problem in the feedback loop eg in chronic kidney disease erythropoietin isn’t made, also in chemo the bone marrow does t respond to the EPO, if bone marrow is infiltrated by fibrous tissue in myelofibrosis, in anaemia of chronic disease eg rheumatoid arthritis iron isn’t made available, to marrow for RBC production, rare blood cancer called myelodysplastic syndromes abnormal clones of marrow cells limit capacity to mae both RBCs and WBCs.
• defects in haem synthesis leads to sideroblastic anaemia, iron deficiency anaemia (not enough iron to make haem), anaemia of chronic disease (enough iron in body but not made available for erythropoeisis), mutations in chain proteins eg alpha and beta thalassaemia, sickle cell disease
• can be inherited:mutations in genes coding for proteins in the cytoskeleton, cells become less flexible and damaged so removed quickly by RES eg hereditary spherocytosis or acquired damage: microangiopathic haemolytic anaemias results from mechanical damage due to sheer stress as cells pass through a valve (eg aortic stenosis narrower opening) produces RBC fragments called schistocytes or cells snag on fibrin strands in small BVs where there’s been increased activation of clotting cascade, other reasons= heat damage from severe burns, osmotic damage by drowning
• G6PDH is in pentose phosphate pathway and produces NADPH for reducing GSSG to GSH, G6PDH deficiency leads to less GSH protection from oxidative stress, can cause lipid peroxidation and protein damage, formation of Heinz bodies. Pyruvate kinase deficiency causes RBCs to rapidly become deficient in glucose since they lack mitochondria & rely on glycolysis, they undergo haemolysis, a rare genetic defect
• acutely blood loss due to injury, surgery, childbirth and ruptured blood vessel. chronic NSAID usage eg aspirin, ibuprofen can lead to GI injury or bleeding. chronic bleeding= a small amount of bleeding continuing over a long time eg heavy menstrual bleeding, repeated nosebleeds, gastrointestinal bleeding
• in haemolytic anaemias, RBCs are destroyed more quickly as they are abnormal or damaged. Damage can happen within blood vessels(intravascular haemolysis) or within the RES system (extra vascular haemolysis), in autoimmune haemolytic anaemias autoantibodies bind to RBCs causing them to recognised by macrophages in the spleen and destroyed, splenomegaly in haemolytic anaemias as spleen is removing lots of RBCs
• myelofibrosis= proliferation of mutated haemopoietic stem cells results in reactive bone marrow fibrosis, little space for haemopoeisis, extramedullary haemopoiesis in liver and spleen
• thalassaemia=Inherited disorders resulting from decrease still absent alpha or beta globin chain production(alpha and beta thalassaemia respectively), imbalance in composition of the haemoglobin chains result in defective microcytic hypochromic red cells. Severity depends on type, lack of 3/4 alpha globin genes leads to haemoglobin H disease

Question 3

• what are the two key features that can help work out the cause of an anaemia?
• what are reticulocytes and why is a reticulocyte count useful?
• give an outline of evaluating anaemias based on these 2 key features.

Answer 3

• The red blood cell size(microcytic, normocytic, macrocytic), presence or absence or reticulocytosis (tells us if bone marrow is responding normally)
• immature red blood cells with no nucleus, take one day to mature into a mature erythrocyte, they are slightly larger than the mature RBCs so an increase in reticulocyte number will increase the main cell volume (MCV)
• reticulocyte increase? Yes=bone marrow working well, is there evidence of haemolysis (high bilirubin & LDH)? Yes=probably enzyme or membrane defects, microangiopathic haemolytic anaemias, autoimmune etc, No=evidence of bleeding ie acute or chronic blood loss.
• increase in reticulocytes? No=problem w bone marrow, what are RBC indices (sizes)?: microcytic=TAILS (thalassaemia, anaemia of chronic disease, iron deficiency, lead poisoning, sideroblastic anaemia), macrocytic= VitB12 deficiency, folate deficiency, liver disease, alcohol toxicity. Normocytic=primary or secondary bone marrow failure

Question 4

• what are macrocytic anaemias? Give the 3 main types
• what is folate, where is it found and stored and what causes of deficiency are there?
• give symptoms of folate deficiency and how much do we need /day?
• why do pregnant and women trying for w baby need to take folate?

Answer 4

• where the average RBC size is bigger than normal.
  1) megaloblastic anaemias=interfere w DNA synthesis during erythropoeisis makes nucleus retarded and smaller compared to cytoplasm, cell division is delayed and erythroblasts grow to form megaloblasts( have a large immature nuclei) that give rise to larger cells eg vit B12/folate deficiency, drugs that interfere w DNA synthesis.
  2) macronormoblastic erythropoeisis= normal relationship between development of nucleus and cytoplasm is retained but erythroblasts are larger than normal eg liver disease, alcohol toxicity
  3) stress erythropoeisis= high reticulocyte count (reticulocytes are larger than normal RBCs eg recovery from blood loss, recovery from haemolytic anaemia
• folate= synthetic form is folic acid, synthesised in bacteria and plants, found in leafy green vegetables, absorbed in jejunum and duodenum, converted to FH4 by intestinal cells, taken up by liver that acts as a store, deficiency due to diet, or increased requirements eg in pregnancy or w increased erythropoeisis, disease of the duodenum or jejunum eg Crohns, alcoholism.
• those related to anaemia, reduced taste, diarrhoea, muscle weakness. Folic acid must be taken before conception and during first 12 weeks of pregnancy to prevent neural tube defects eg spina bifida
• 400 micrograms/day

Question 5

• what is vitamin B12 and what is it required for?
• what are some good sources of vitamin B12
• how is Vitamin B12 absorbed?
• what are some causes of Vitamin B12 deficiency
• give symptoms of vitamin B12 deficiency

Answer 5

• a water soluble vitamin, essential co factor for DNA synthesis due to its role in folate mechanism so is required for normal erythropoeisis & normal CNS development, produced by bacteria ONLY
• meat, fish, eggs, milk, yeast extract
• B12 is released from food proteins by proteolysis in the stomach where it then binds to haptocorrin, the haptocorrin B12 complex is digested by pancreatic proteases in the s intestine releasing B12 which then binds to intrinsic factor. Intrinsic factor B12 complex then binds to Cubam receptor which mediates uptake of complex by receptor mediated endocytosis into enterocytes. After lysosomal release in enterocytes, B12 exits via basolateral membrane through MDR1, binds to transcobalamin in blood and transported around bloodstream where majority is stored in liver (enough for 3-6 yrs)
• dietary deficiency, lack of intrinsic factor (pernicious anaemia-where you have decreased or absent intrinsic factor, causes progressive exhaustion of B12 reserves, auto immune- 2 types of antibody: Blocking Ab blocks binding of B12 to IF (more common) and binding Ab prevents receptor mediated endocytosis), lack of transcobalamin,
• symptoms= those related to anaemia, glossitis, diarrhoea

Question 6

• how can a B12 deficiency cause CNS problems? What is the name of the serious condition that can arise and it’s symptoms?
• how are B12 and folate ‘linked’?
• why do B12 and folate deficiency cause megaloblastic anaemia?
• how would a megaloblastic anaemia appear in a full blood count?
• treatment of vit B12 and folate deficiency?

Answer 6

• it’s associated w focal demyelination, often is a reversible neuropathy BUT can cause a serious condition called subacute combined degeneration of the cord which is irreversible.symptoms= gradual onset weakness, changes in mental state.
• because lack of B12 will trap folate in the stable methyltetrahydrofolate form preventing its use in other reactions eg thymidine deficiency for DNA synthesis.
• both folate and B12 deficiency will lead to thymidine deficiency, so uracil is put into DNA instead, DNA repair enzymes detect this and excise them, resulting in asynchronous maturation between nucleus and cytoplasm (nucleus doesn’t fully mature, cytoplasm matures normally) results in large cells w lots of cytoplasm
• low Hb, raised mean cell volume, low RBC count, lactate raised bc of increased cell destruction, bilirubin raised for same reason
• treated w folic acid, vit B12 supplements( beware of hypokalaemia at first bc more K+ is needed as erythropoeisis returns to its normal rate), blood transfusion for patients w B12 deficiency can cause high output cardiac failure, need to transfers small volumes.