CAUSES AND TYPES OF ANAEMIA

CAUSES AND TYPES OF ANAEMIA

definition of anaemia
 
is the reduction in the concentration of circulating haemoglobin below the expected range for age and sex ,eg  adult male:<13 g\dl adult female<11.5 g\dl it may be acute or chronic anaemia 
mechanism of anaemia causes 1- decreases production as impaired erythrocyte formation or impaired erythrocyte function 2- increased loss as blood loss either acute or chronic and decreased erythrocyte lifespan eg. haemolysis nb. physiological anaemia occurs in pregnancy due to a relative increase in plasma volume . anaemia may be classified by cause or by the effects on cells when viewed as a blood film


classification of anaemia

the blood film , anaemia can be classified according to the morphological appearances of erythrocytes on blood film so we look at the mean cell volume (MCV)  to determine whether the cells are too small (microcytic) too large (macrocytic) or normal size normocytic
the intensity of colour of blood cells as seen on the blood film is also important as cell colour can be decreased with central pallor (hypochromic) or normal normochromic

what are the causes of anaemia ?

it can be classified as 1- microcytic hypochromic red cell appearance like

  • iron deficiency like malabsorption , chronic blood loss usually GI or GU tract decreased dietary intake and increased demand 2-normocytic normochromic red cell appearance as 
  • acute blood loss
anaemia of chronic disease
  • endocrine disease
  • malignancy
as erythrocyte abnormality
 as spheroctosis ,elliptocytosis , G-6-deficiency
  • haemoglobin abnormality
  • extrinsic factors as DIC infection , chemical injury sequestration
  • macrocytic red cell appearance as
  •  megablastic interference with DNA synthesis causing morphological abnormalities
  • folate or folic acid deficiency
  • vit B12 deficiency as prenicious anaemia ,gastroectomy ileal resection crohn,s disease
  • drugs as azathioprine azt hydroxyurea methothrexate
  • non megablastic anaemia as liver disease alcohol pregnancy hypothyroidism and increased reticulocyte number
  • clinical effects of anaemia clinically anaemia becomes apparent when the oxygen demands of tissue cannot be met without some form of compensatory mechanism . a slowly falling haemogolbin level allows for tissue acclimatisation . compensatory mechanisms include a tachycardia and increased cardiac output and chronically a reticulocytosis due to increased erythropoiesis and increased oxygen extraction from the blood ,when the patient is relatively anaemic the blood has a lower haematocrit and decreased viscosity , this improves blood flow through the capillaries and so in case of critical illness patients requiring transfusion may not have their anaemia corrected beyond 9-10 g\dl 
  • anaemia is not a diagnosis . if the patient presents with low haemoglobin it is important to look for a cause although emergency surgery should not be delayed . when there is no time for futher preoperative investigations , correction of anaemia by blood transfusion may be required to be part of resuscitation whilst surgical intervention is ongoing 
  •  reversible causes of anaemia should be corrected before elective surgery mildly anaemic patients who are otherwise well may tolerate general anaesthesia and surgery well . more profound anaemia should be treated by consideration of transfusion , iron supplementation etc
  • how to investigated anaemia 1- history
  • acute or chronic blood loss as in menorrhagia bleeding per rectum 
  • insufficient dietary intake of iron and folate as in elderly poverty anorexia alcoholic
  •  excessive utlisation of important factors as in pregnancy prematurity
  •  malignancy
  •  chronic disorders as in malabsorption state affecting the small bowel
  •  drugs as phenytoin antagonises folate
  • further investigation of anaemia a peripheral blood film will show the morphology of the anaemia and then investigations can be tailored to the particular classification , it is important to look at low haemoglobin in relation to the leucocyte and platelet counts to consider a pancytopenia , a reticulocyte count indicates bone marrow activity 
  • tests for haemolysis include serum bilirubin (unconjugated) urinary urobilinogen heptoglobin and haemosidernuria , a schilling,s test is undertaken in suspected b12 deficiency  a bone marrow biopsy may be considered and other tests where relevant such as thyroid function tests and  G-GT(gamma - glutamyl transferase)
  • specific investigations for iron deficiency include blood tests such as ferritin transerrin and total iron binding capacity . vitamin c increases iron absorption
  • examine the source of blood loss as GI tract upper and lower endoscopy renal tract IVP cystoscopy menorrhagia etc . replacement therapy should comprise 200 mg ferrpus sulphate t.d.s
  • folate deficiency (folate found in green vegetables and offal ) may be due to insufficient intake or excessive utilisation as in pregnancy NB  subsequent deficiency of folate causes neural tube defects . measurement of red cell folate (160-640 g|l) is more accurate than serum levels also exclude vitamin b12 deficiency as administration of folate will aggravate neuropathy . replacement therapy should consist of 5 mg folate once daily . if possible these investigations should be send off before commencement of iron or blood transfusion which will obscure the results

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