Macrocytosis and Macrocytic Anaemia Flashcards
what is the MCV value in macrocytosis?
> 100
what is a megaloblast?
abnormally large, nucleated red cell precursors
macrocytosis can occur with or without anaemia - true or false?
true
megaloblastic anaemias can be characterised into what two things?
megablastic
non megaloblastic
how does macrocytosis occur?
cells become larger due to defective nuclear maturation and DNA synthesis during haematopoesis
this results in growth without division prior to nucleus extrusion (therefore, large cell size created by failure to become smaller opposed to cells becoming larger)
what is megablastic anaemia?
large precursor cells with an immature nucleus leading to macrocytic anaemia
due to their size, macrocytic cells are more prone to what?
early breakdown
what are the different causes of macrocytosis?
megaloblastic macrocytic anaemia
non megaloblastic macrocytosis
what are the different causes of megaloblastic macrocytic anaemia?
B12 and folate deficiency
drugs: cytotoxics
a deficiency in either B12 or folate can impact the functioning of the other - true or false?
true
where is B12 mainly sourced from?
animal foods
where is B12 absorbed?
in the terminal ileum via binding to intrinsic factor
is the body store of B12 small or large?
large - lasts 2-4 years
where is folate mainly obtained from?
plant foods, especially leafy green vegetables
where is folate absorbed?
duodenum
is the body store of folate small or large?
much smaller than B12, meaning the body will become deficient in folate before B12
what are dietary causes of B12 deficiency?
vegan diet
alcoholism
old age
what conditions cause reduced absorption of B12 in the stomach?
pernicious anaemia
gastrectomy
PPI
anti histamine
what conditions cause reduced absorption of B12 in the small intestine?
bacterial overgrowth
coeliac disease (affects terminal ileum)
chrons disease
bowel resection
what conditions cause reduced absorption of B12 in the pancreas?
chronic pancreatitis
what is pernicious anaemia?
autoimmune atrophic gastritis in which there is reduction in the production of HCL and intrinsic factor
who is pernicious anaemia most commonly seen in?
women in their 40s with other autoimmune conditions (thyroid, addisons, vitiligo)
what autoantibodies are seen in pernicious anaemia?
anti gastric parietal cell = sensitive but not specific
anti intrinsic factor = specific but not sensitive
what is the treatment of pernicious anaemia?
B12 injections for life
what are circumstances which cause low intake of folate?
poverty
old age
alcoholism
what conditions cause malabsorption of folate leading to folate deficiency?
coeliac disease
tropical sprue
what conditions cause increased demand of folate leading to folate deficiency?
pregnancy malignancy myelofibrosis exfoliating dermatitis haemolytic anaemia
what drugs cause folate deficiency?
methotrexate
trimethoprim
alcohol
anticonvulsants: phenytoin, valproate
as well as the symptoms of anaemia, what else can be seen in megaloblastic macrocytic anaemia?
mouth: glossitis / angular stomatitis
jaundice: due to chronic haemolysis
psychiatric: irritability, depression
neurological (more with B12): numbness, tingling, subacute degeneration of spinal cord
weight loss, diarrhoea, infertility
what is sub acute combined degeneration of spinal cord and how does it present?
insidious degeneration of corticospinal tract and dorsal columns
presentation: parasthesia, ataxia, weakness (sensory symptoms tend to occur first?
what is seen on investigation in megaloblastic macrocytic anaemia?
serum: low B12/folate
FBC: low Hb, high MCV, reticulocytes
bone marrow biopsy: megalolasts
film: howel jolly bodies, macrovalocytes and hypersegmented neutrophils
how is megaloblastic macrocytic anaemia treated?
identify and treat underlying cause
folate deficiency = 5mg for 4 months
B12 deficiency = B12 injections (initially on alternative days, then 3 monthly if appropriate)
transfuse red cells only if life threatening
why should folate not be given alone in megaloblastic macrocytic anaemia?
due to failing to provide B12, precipitating or worsening subacute combined degeneration of cord
all the causes of non megaloblastic macrocytosis cause an increase in red cell size by what?
altering the red cell membrane
what are the main causes of non megaloblastic macrocytosis?
alcohol
pregnancy
hypothyroidism
liver disease (target cells on blood film)
marrow failure (myelodysplasia, aplastic anaemia)
what is the difference between marrow failure as a cause of non megaloblastic macrocytosis and the other causes eg alcohol?
marrow failure will always present with anaemia
what is reticulocytosis?
increased amounts of circulating reticulocytes due to increased production of RBCs
occurs as marrow response to acute blood loss or red cell breakdown (haemolysis)
are reticulocytes bigger or smaller than mature RBCs?
bigger
they are analysed along with these for MCV measurement
in what conditions is reticulocytosis seen in?
haemolysis
haemorrhage
treatment of anaemia
thalassemia (will cause reticulocytosis but not macrocytosis)
other than reticulocytosis, what is another kind of spurious (fake) macrocytosis?
cold agglutinin disease
