Anaemias Flashcards
what is haematocrit
%RBC of blood volume
in what scenarios is Hb not a good indicator of anaemia
if the patient has lost a large volume of blood
if the patient has been given saline fluids
what are the 2 classifications of anaemia
microcytic
macrocytic
what determines if an anaemia is microcytic or macrocytic
mean cell volume
low = microcytic (small erythrocytes, less of them)
high = macrocytic (big erythrocytes, less of them)
where in the erythrocyte is Hb synthesised
cytoplasm
microcytic erythrocytes have high/low volumes of Hb
low
what kind of anaemia is caused by lack of raw materials
microcytic
less Hb made, cells are smaller
what are features of Hb deficient microcytic erythrocytes
hypochromic - lacking in red colour
pencil cells
target cells
what might cause iron deficiency
heavy periods (blood loss)
lack of dietary iron (uncommon in this country)
anaemia of chronic disease - iron levels normal, not bioavailable
GI blood loss
malabsorption of iron (e.g. coeliac)
what might cause porphyrin deficiency
lead poisoning
pyridoxine responsive anaemia
what might cause globin deficiency
thalassaemia
if a patient has lost 1L blood, how much iron have they lost
500ml
iron loss = 1/2 blood loss
where is iron stored
macrophages (from RBC breakdown)
liver
haemoglobin
where does most iron exist
Hb
what is circulating iron bound to
transferrin
when is %saturated transferrin decreased
iron deficiency
anaemia of chronic disease
when is %saturated transferrin increased
haemachromatosis
how is iron stored in liver
as ferritin
how do you measure storage iron
serum ferritin
how is iron deficiency confirmed
combination of low Hb (functional iron) and low serum ferritin (low storage iron)
where is dietary iron absorbed from
proximal small bowel
what are the 2 true causes of macrocytic anaemia
megaloblastic
non-megaloblastic
what is a megaloblast
abnormally large nucleated red cell precursor with an immature nucleus
what is defective in megaloblastic macrocytic anaemias
DNA synthesis and nuclear maturation
preserved Hb and RNA synthesis
why are megaloblasts bigger than normal cells
divides fewer times
however Hb still accumulates in cytoplasm eventually triggering enucleation
left with larger RBCs but less of them
what are causes of megaloblastic macrocytic anaemias
B12 and folate deficiencies
Drugs
inherited abnormalities of enzymes
why does B12 and folate deficiency cause megaloblastic anaemia
they provide enough nucleosides for DNA synthesis which allows DNA replication to occur
what biochemical pathway does folate catalyse
uridine to thymidine
what is the only source of B12
meat and animal food - cobalamine
where is B12 released from food
stomach - acidic environment
what binds to B12 and where
intrinsic factor
form a complex in proximal small bowel
what secretes intrinsic factor
parietal cells in fundus and body of stomach
where is the B12-intrinsic factor complex absorbed
terminal ilium
what are causes of B12 deficiency
vegans
stomach problems - atrophic gastritis, pernicious anaemia
small bowel - coeliac, bacterial overgrowth, crohn’s
what is pernicious anaemia
autoimmune condition resulting in destruction of gastric parietal cells
consequences of ineffective gastric parietal cells
no intrinsic factor secreted
therefore B12 cannot be absorbed
what are conditions associated with pernicious anaemia
other autoimmune conditions:
hypothyroid
vitiligo
Addison’s
how is folate absorbed
dietary folates converted to monoglutamate
absorbed in jejunum
what are sources of folate
leaf veg and yeast
causes of folate deficiency
inadequate dietary intake
malabsorption - coeliac, crohn’s
excess utilisation - pregnancy, malignancy, exfoliating dermatitis, haemolysis
drugs - anticonvulsants
folate/B12 is more likely due to inadequate dietary intake. Why?
Folate - stores are only last for 4 months
B12 stores last 2-4 years
what are clinical features of both B12/folate deficiency
anaemia weight loss diarrhoea infertility sore tongue jaundice developmental problems in children
neurological problems can occur in B12/folate deficiency
B12
why do neurological problems occur in B12 deficiency
B12 involved in the formation of myelin
neurological manifestations of B12 deficiency
dorsal column abnormalities
neuropathy
dementia
psychiatric manifestations
what might the blood film show in macrocytic anaemia
macrovalocytes and hypersegmented neutrophils (3-5 nuclear segments)
what anti-bodies indicate pernicious anaemia
anti gastric-parietal cell (antiGPC)
anti intrinsic factor (antIF)
what antibody is more specific to pernicious anaemia
antiIF
what medication is given to treat B12 deficiency
hydroxycobalamin IM
loading dose for 2 weeks then three monthly life-long
what medication is given to treat folate deficiency
folic acid 5mg/day oral
when would you do a blood transfusion due to macrocytic anaemia
if life threatening
what are causes of non-megaloblastic macrocytic anaemia
alcohol
liver disease
hypothyroid
bone marrow failure (myelodysplasia, myeloma, aplastic anaemia)
why might MCV be measured as high when it is actually normal
increase in reticulocyte numbers as a response to acute blood loss
cold-agglutinins - clumps of agglutinated red cells which may register as one giant cell
why might patients with pernicious anaemia appear mildly jaundiced
intramedullary haemolysis - causes premature red cell death. Results in release of Hb which is conveted to bilirubin
