Pathology · Short notes

Haematological Disorders: Short Notes & Cheat Sheet

Anaemias by red cell size, thalassaemia and haemolytic anaemias, bleeding disorders and clotting tests, leukaemias, lymphomas and myeloma.

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Short notes

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Classifying anaemia by red cell size

increasing mean cell volume (MCV)MicrocyticMCV < 80 fLIron deficiency, thalassaemia,chronic diseaseNormocytic80–100 fLBlood loss, haemolysis, CKD, aplasticMacrocyticMCV > 100 fLB12/folate, alcohol, liver,hypothyroid
The MCV narrows the cause quickly; ferritin then separates iron deficiency from thalassaemia and chronic disease.

Anaemias

  • WHO defines anaemia as haemoglobin below 13 g/dL in men, 12 g/dL in women and 11 g/dL in pregnancy.
  • Microcytic (MCV below 80 fL): iron deficiency (low ferritin, high TIBC; the commonest), thalassaemia, anaemia of chronic disease and sideroblastic anaemia.
  • Normocytic: acute blood loss, haemolysis, chronic kidney disease (low erythropoietin) and aplastic anaemia.
  • Macrocytic (MCV above 100 fL): megaloblastic from B12 or folate deficiency (hypersegmented neutrophils), or non-megaloblastic from alcohol, liver disease or hypothyroidism.
  • β-thalassaemia major needs lifelong transfusion and iron chelation. Pakistan has a high carrier rate, so carrier screening before marriage is encouraged.

Haemolysis and bleeding

  • Haemolysis raises unconjugated bilirubin, LDH and reticulocytes and lowers haptoglobin.
  • Causes: hereditary spherocytosis, G6PD deficiency (bite cells, Heinz bodies), sickle cell disease (valine replaces glutamate at position 6 of the β chain) and autoimmune haemolysis (positive Coombs test).
  • PT tests the extrinsic pathway (factor VII) and monitors warfarin (as INR). aPTT tests the intrinsic pathway (VIII, IX, XI, XII) and monitors unfractionated heparin.
  • Haemophilia A (factor VIII) and B (factor IX) are X-linked and prolong the aPTT. Von Willebrand disease is the commonest inherited bleeding disorder; desmopressin can help.
  • DIC: prolonged PT and aPTT, low platelets and fibrinogen, high D-dimer.

Blood cancers

  • ALL is the commonest childhood cancer. AML affects adults and shows Auer rods; acute promyelocytic leukaemia (t(15;17)) responds to ATRA.
  • CML has the Philadelphia chromosome t(9;22) creating BCR-ABL, treated with imatinib. CLL affects the elderly and shows smudge cells.
  • Hodgkin lymphoma has Reed–Sternberg cells; non-Hodgkin lymphomas are a larger, varied group.
  • Multiple myeloma is a plasma cell cancer: high calcium, renal failure, anaemia and bone lesions (CRAB), with an M-spike and Bence Jones protein.
  • Polycythaemia vera is linked to the JAK2 mutation.

Cheat sheet

High-yield facts in one place. Cover the right-hand column and test yourself.

Clotting tests

TestPathway · used for
PT / INRExtrinsic (VII) · warfarin
aPTTIntrinsic (VIII, IX, XI, XII) · heparin, haemophilia
Platelet countThrombocytopenia
Bleeding time / PFAPlatelet function, von Willebrand
D-dimerFibrin breakdown: DIC, VTE

Blood cancers

DiseaseHallmark
ALLCommonest childhood cancer
AMLAuer rods; APL t(15;17) → ATRA
CMLPhiladelphia t(9;22), BCR-ABL → imatinib
CLLElderly; smudge cells
Hodgkin lymphomaReed–Sternberg cells
Multiple myelomaCRAB, M-spike, Bence Jones
Polycythaemia veraJAK2 mutation

Memory aids

CRAB
Myeloma: hyperCalcaemia, Renal failure, Anaemia, Bone lesions.
PT = warfarin (WEPT), aPTT = heparin (HINT)
Warfarin affects the Extrinsic pathway measured by PT; Heparin affects the INTrinsic pathway measured by aPTT.

Exam traps

  • Ferritin is low in iron deficiency but normal or high in anaemia of chronic disease and thalassaemia.
  • Haemophilia prolongs aPTT but not PT.
  • Hypersegmented neutrophils suggest megaloblastic anaemia.
  • Von Willebrand disease, not haemophilia, is the most common inherited bleeding disorder.

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