haematology

• Haemopoiesis

  Production of blood cells

  
• Site of haemopoiesis

  • Red marrow in infancy (all bone marrow is haemopoietic) → fatty replacement in childhood → yellow marrow in adults (50% of bone marrow is fat)
  • Fat marrow may revert to hemopoietic marrow in cases of increased demand (excessive blood loss, haemolysis)
  • Extramedullary haemopoiesis: outside bone marrow, usually liver and spleen in adult life (thalassemia)
• Microenvironment for haemopoiesis

  • Stromal cells (endothelial cells, fibroblasts, macrophages) provide adhesion molecules and growth factors
• Growth factors

  Determine lineage for differentiation of haemopoietic cells
• Erythropoiesis

  Myeloid progenitor → committed erythroid progenitor cells → proerythroblast → early/basophilic erythroblast → intermediate/polychromatophilic erythroblast → late/orthochromatic erythroblast → reticulocyte → mature red blood cell

  
• Red blood cell morphology during development

  • Cell diameter decreases
  • Cytoplasm changes from blue to pink
  • Nuclear diameter decreases
  • Nuclear colour changes from purple-red to very dark blue
  • Nuclear chromatin becomes condensed

  
• Erythropoietin (EPO)


  • Hormone that regulates erythropoiesis
  • Produced by perisinusoidal cells in the liver during fetal/perinatal period
  • Produced by peritubular interstitial fibroblasts in the renal cortex in adulthood
  • Regulated by hypoxia-inducible factors (HIFs) - hypoxia stimulates EPO production, increased RBCs and oxygen inhibits EPO
• Structure and function of erythrocyte

  • Lipid bilayer cell surface membrane (deformable and flexible)
  • Cytoplasm containing haemoglobin (carries oxygen)
  • No nucleus (more room for haemoglobin)
  • Bi-concave disc shape (increased surface area for oxygen absorption)
  • No mitochondria or organelles (produce ATP from glycolysis, do not use oxygen)
• Haem synthesis


  1. Starts with condensation of glycine + succinyl CoA in presence of B6

  2. 8 enzymatic steps: 4 in mitochondria, 4 in cytosol

  3. Last stage: protoporphyrin + Fe2+ = heme
• Haemoglobin


  • 4 haem + 4 globin chains
  • 2 alpha and 2 non-alpha subunits
  • Alpha and non-alpha chains produced in equal quantities
  • Healthy adults: 96% HbA (2α 2β), 3% HbA2 (2α 2δ), 1% HbF (2α 2γ)
• Normal destruction of red blood cells

  1. Porphyrin broken down to bilirubin

  2. Bilirubin bound to albumin and transported to liver

  3. In liver, bilirubin bound to glucuronic acid and becomes conjugated and soluble

  4. Enters gut through bile duct, bacteria convert to urobilinogen

  5. Urobilinogen reabsorbed and excreted in urine (dark colour)

  6. Oxidised to stercobilin in bowel (gives faeces dark colour)

  
• Full blood count results

  • Hct: Hematocrit (percentage of blood volume as RBCs, RV 45%)
  • Hb: Hemoglobin concentration (g/dl)
  • RBC: Red Blood Cell count (RV 5 x 10^6/μl)
  • MCV: Mean Corpuscular Volume (average size of RBC, RV 80-96fL)
  • MCH: Mean Corpuscular Hemoglobin (average Hb content of RBC, RV 26-32pg)
  • MCHC: Mean Corpuscular Hemoglobin Concentration (average Hb concentration in Hct, RV 32-36g/dl)
  • RDW: Red Cell Distribution Width (range of deviation around average size, RV 11.5-14.5%, indicates anisocytosis)
• Microcytic anaemia


  MCV <80fl
• Anaemia


  Reduction in concentration of Hb, Hct, or RBC below normal range for age and sex
• Causes of microcytic anaemia

  • Iron deficiency anaemia
  • Thalassemia/hemoglobinopathy
  • Anaemia of chronic disease (associated with IDA)

  
• Anaemia reference values


  • Hb <11g/dl: children up to 5yrs
  • Hb <13g/dl: men
  • Hb <12g/dl: women
  • Hb <11g/dl: pregnancy
• Causes of normocytosis (80-100 fL)

  • Aplastic anaemia
  • Anaemia of chronic disease (onset)
  • Hemolytic anaemia
• Causes of macrocytosis (>100 fL)

  • Megaloblastic anaemia
  • Non-megaloblastic anaemia
• Classification of anaemia


  Based on red blood cell size and reticulocyte count

  
• Anaemia


  Reduction in concentration of Hb, Htc, or RBC below normal range for age and sex
• Reticulocyte count


  • Reticulocyte (%) = [Number of Reticulocytes / Number of total Red Blood Cells] X 100 (RV 0.5 – 2.0 %)
  • Immature circulating erythrocytes
  • Mature after 24hrs in peripheral blood
  • Used as a marker to monitor recovery after treatment
  • Represent an indicator of bone marrow turnover

  
• Normal Hb levels


  • Children up to 5yrs: Hb <11g/dl
  • Men: Hb <13g/dl
  • Women: Hb <12g/dl
  • Pregnancy: Hb <11g/dl
• Causes of low reticulocyte count (hypo-proliferative anaemia)

  • Lack of nutrients (iron, folic acid, B12)
  • Chronic diseases
  • Bone marrow disorder (aplastic anaemia, leukaemia)
  • Bone marrow suppression (chemotherapy)
• Macrocytic anaemia, megaloblastic and non-megaloblastic


  • Importance of medical history and main signs/symptoms for correct diagnosis
  • Common causes of macrocytic anaemia and macrocytosis without anaemia
  • Nutritional and metabolic aspects of vitamin B12 and folate
  • Concept of megaloblastic anaemia and effect of B12 and folate deficiency on DNA synthesis
  • Comparison of megaloblastic and non-megaloblastic anaemia
  • Differences between B12 and folate deficiency
  • Signs, symptoms and lab diagnosis of macrocytic anaemia
  • Investigation and management of B12 and folate deficiency

  
• Causes of high reticulocyte count (hyper-proliferative anaemia)


  • Haemolytic anaemia
  • Chronic blood loss
• Symptoms of anaemia


  • Nonspecific: Weakness, fatigue, inability to concentrate, irritability, headache
  • Cardiorespiratory: Dyspnea with exercise, tachycardia, palpitations, hypotension, faint, chest pain, angina
  • Neuromuscular: Muscular weakness, headache
• Vitamin B12 and folate (B9) are needed for DNA synthesis
• Deficiencies impair DNA replication, halt cell division, and increase apoptosis, leading to ineffective haemopoiesis and megaloblastic morphology of erythrocyte precursors
• Mechanisms of anaemia production and aetiology

  • Central type: Bone marrow defect (leukaemia, myelodysplastic syndromes, myelofibrosis, aplastic anaemia, metastases)
  • Peripheral type: Decreased production (deficiency of haematinic substances, chronic disease with EPO deficiency)
  • Peripheral type: Increased destruction/haemolysis (hypersplenism, autoimmune diseases, haemoglobinopathies)
  • Peripheral type: Blood loss (physiological - menstruation, pathological - bleeding)
• Signs of anaemia


  • Pale conjunctiva, brittle nails, koilonychia (spoon nails), platonychia (flat nails), skin dryness, dryness and brittleness of hair
  • Conjunctival rim pallor is more sensitive than hand pallor
• Vitamin B12 deficiency is associated with peripheral neuropathies and neuropsychiatric abnormalities due to demyelination of nerves
• Causes of microcytic anaemia

  • Low ferritin and iron → iron deficiency anaemia
  • Normal ferritin and iron → thalassemia/hemoglobinopathy
  • High ferritin and iron → anaemia of chronic disease, sideroblastic anaemia

  
• Folate and vitamin B12 deficiency can lead to elevation in homocysteine, which is a thrombotic risk factor for coronary artery disease
• Absorption of Vitamin B12

  Vitamin B12 combines with intrinsic factor (glycoprotein), forming a complex that is absorbed at terminal ileum by pinocytosis. Intrinsic factor is produced in parietal cells in stomach.
• Problems in production of Hb causing hypochromic microcytic anaemia

  • Lack of iron → iron deficiency
  • Lack of iron release → chronic inflammation
  • Defects in synthesis of haeme → porphyria
  • Defects in incorporation of iron into the haeme → sideroblastic anaemias
  • Qualitative defects of globin chain synthesis → hemoglobinopathies (e.g. sickle cell)
  • Quantitative defects of globin chain synthesis → hemoglobinopathies (e.g. thalassemia)

  
• Causes of impaired absorption of Vitamin B12


  • Pernicious anaemia (autoimmune destruction of gastric parietal cells)
  • Inherited intrinsic factor deficiency
  • Small intestine disease (resection, Crohn's, tropical sprue)
  • Small intestine parasites and bacteria (fish tapeworm, blind loop syndrome, SIBO, diverticulus)
  • Drugs (nitrous oxide, omeprazole, metformin, colchicine, neomycin)

  
• Signs and symptoms of iron deficiency anaemia

  • Skin pallor, pale conjunctiva, brittle nails, platonychia, koilonychia, skin dryness, dryness and brittleness of the hair, angular cheilitis, painful glossitis, atrophic gastritis, pica

  
• Function of B12 and folic acid

  • Methylation of homocysteine to methionine
  • Conversion of methylmalonyl CoA to succinyl CoA
  • Synthesis of DNA by conversion of deoxyuridine monophosphate to deoxythymidine monophosphate
• Plummer Vinson syndrome


  Syderopenic dysphagia due to iron deficiency, difficulty in swallowing leading to glossitis, angular cheilitis, esophageal web. Premalignant condition → squamous cell carcinoma. Treatment: esophageal dilation and iron
• Causes of Vitamin B12 deficiency

  • Decreased dietary intake (poor diet)
  • Malabsorption (intrinsic factor deficiency, small intestine disease, parasites/bacteria, drugs)