Microcytic anaemia Flashcards
what is anaemia
reduced total red cell mass
how is total red cell mass measured
Hb used as a surrogate marker (spectrophotometric method)
as it haematocrit (ratio or percentage of whole blood that is red cells)
what are the Hb levels that suggest anaemia
adult males <130
adult females <120
when might Hb/hct not be a good marker of anaemia
when patient not in a steady state- e.g. rapid blood volume loss, plasma expansion (haemodilution)
what is the reaction to anaemia
reticulocytosis (usually takes a few days- in massive haemorrhage can produce some quicker)
what are reticulocytes
red cells that have just left the bone marrow
larger than mature cells, still have RNA remnants - stain purple as a result
appear polychromatic on blood film
what does reticulocyte count assess
marrow response
what does blood film assess
cellular morphology
what are the two pathophysiological types of anaemia
decreased production- low reticulocyte count, not producing cells
increased loss or destruction of red cells- high reticulocyte count, lots of immature cells trying to replace loss
what can cause decreased rbc production
hypoproliferative- reduced amount of erythropoiesis
maturity abnormality- erythropoiesis present but ineffective: cytoplasmic defects (impaired haemoglobulinisation, nuclear defects causing impaired cell division)
what can cause increased loss of destruction of rbcs
bleeding
haemolysis (premature red cell degeneration)
how is anaemia classified in practise
using cell size and Hb content
what does a low MCV mean
microcytic
(in the context of low reticulocyte count) =cytoplasmic defect resulting in problems with haemoglobinisation
what does a high MCV mean
macrocytic
(in the context of low reticulocyte count) = nuclear defect causing impaired cell division and maturation
what does anaemia with a normal MCV count mean
hypoproliferative problem
where does haemoglobin synthesis occur
in the cytoplasm - defects in this leads to small cells= microcytic
what is needed to make Hb
globins
haem (porphyrin ring, iron (Fe2+)
what colour are cells with deficiency in Hb
hypochromic
what type of anaemia results from inability to make Hb
microcytic
what can cause hypochromic microcytic anaemias
deficient haemoglobin synthesis (cytoplasmic defect):
haem deficiency
-IRON DEFICIENCY
-anaemia of chronic disease (these usually normocytic)
porphyrin ring synthesis
-lead poisoning
globin deficiency
-THALASSAEMIA (problem of globin chain synthesis)
what states can iron exist in
Fe2+ or Fe3+
what is the role of iron
oxygen transport as Hb or myoglobin
electron transport in ATP production in mitochondria
describe the composition of haemoglobin
4 globin protein subunits (2 alpha 2 beta) each contains a single haem molecule
haem molecule contains single Fe2+ ion and can bind with a single O2 molecule
when fully saturated how much O2 will bind to 1g of Hb
1.34ml
how is iron stored in the body
most is in haemoglobin
rest in liver and macrophage stores as the molecule ferritin (mainly in liver)
what is circulating iron bound to
transferrin (this feeds it tobone marrow macrophages that then feed it to red cell precursors)
what are the tests that assess iron status
function iron- Hb
transported iron- serum iron, transferring, transferring saturation
stored iron- serum ferritin
what is transferrin
protein with two binding sites for iron atoms that transports iron from donor tissues (macrophages, intestinal cells, hepatocytes) to tissues expressing transferrin receptors (erythroid marrow)
what can alter the % saturation of transferrin with iron
reduced in iron deficiency
reduced in anaemia of chronic disease
increased in genetic haemachromatosis
what is ferritin
large intracellular protein that stores ferric ions
why is only a small amount of ferritin present in serum
as intracellular
what is serum ferritin a measure of
indirect measure of storage iron
low ferritin means iron deficiency
what does low ferritin mean
iron deficiency
what can cause increased ferritin
in the acute phase of an infection
what confirms irons deficiency
anaemia (decreased functional iron)
and
reduced storage iron (low serum ferritin)
what can cause iron deficiency
diet: relative deficiency (women of childbearing age), absolute deficiency (veggies/vegans)
(diet unusual to cause deficiency in men)
blood loss: usually GI, menorrhagia
malabsorption: coeliac disease, achlorhydia (e.g. people on PPIs, need acid to absorb iron)
where in GI tract do you absorb iron
proximal small bowel (e.g. affected in coeliac)
what are potential causes of chronic blood loss
menorrhagia
GI- tumours, ulcers, NSAIDs
haematuria
what is the average daily intake of iron
1mg/day
in menorrhagia loose >30mg/ month
what are the consquences of low iron
exhaust iron stores (ferritin will go down)
iron deficient erythropoiesis (falling red cell MCV)
epithelial changes: skin, koilonychia
what is occult blood loss
when small volume of GI blood loss can occur without any symptoms/ signs
this can outstrip the maximum dietary iron absorption = anaemia
is iron deficiency anaemia a diagnosis or a symptom
symptom- need to investigate and find underlying cause
what is the risk or iron replacement therapy
relieve symptoms without treating underlying problems
