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Blood Film
 
 

Platelet Morphology

 
 
 
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Overview

Platelets are very small non-nucleated cells with fine granules that derive from fragmentation of megakaryocytes.
  •  

Thrombocytosis

Thrombocytosis is an increase in the number of circulating platelets. This may be primary, in the context of myeloproliferative neoplasms, or secondary to another process.
  • Thrombocytosis
     
  • Causes of Thrombocytosis

  • Primary

  • Myeloproliferative neoplasms - essential thrombocythaemia, polycythaemia vera, chronic myeloid leukaemia, myelofibrosis
  • Secondary

  • Infection
  • Inflammation - autoimmune disease, major surgery, trauma, fracture, burns, pancreatitis, infarction
  • Malignancy
  • Post splenectomy
  • Iron deficiency anaemia
  • Acute haemorrhage
  • Acute haemolysis
  • Drugs - adrenaline, corticosteroids, vinca alkaloids, thrombopoietin

Thrombocytopaenia

Thrombocytopaenia refers to a reduction in the number of circulating platelets.
In a patient with new thrombocytopaenia, look for platelet clumping and fibrin strands which may indicate a factitiously low platelet count, or pseudothrombocytopaenia.
  • Causes of Thrombocytopaenia

  • Reduced Production

  • Congenital thrombocytopaenia
  • Bone marrow failure - aplastic anaemia, paroxysmal nocturnal haemoglobinuria
  • Bone marrow suppression - cytotoxic chemotherapy, radiotherapy, alcohol abuse
  • Bone marrow infiltration - leukaemia, multiple myeloma, lymphoma, metastasis, myelofibrosis
  • Myelodysplasia
  • B12 / folate deficiency
  • HIV infection
  • Increased Destruction

  • Idiopathic thrombocytopaenic purpura (ITP)
  • Heparin-induced thrombocytopaenia (HIT)
  • Drug-induced thrombocytopaenia - heparin, quinine, bactrim, vancomycin, rifampin, paracetamol, NSAIDs, glycoprotein IIb/IIIa inhibitors
  • Immune thrombocytopaenia - SLE, antiphospholipid syndrome, rheumatoid arthritis, transfusion reaction
  • Thrombotic microangiopathies - thrombotic thrombocytopaenic purpura (TTP), haemolytic-uraemic syndrome (HUS), disseminated intravascular coagulation (DIC)
  • Infection - hepatitis C, EBV, CMV, H pylori, sepsis
  • Pregnancy - gestation thrombocytopaenia, preeclampsia / HELLP syndrome
  • Splenic Sequestration

  • Hypersplenism
  • Factitious

  • Platelet clumping
  • Haemodilution (e.g. massive transfusion)

Abnormal Platelet Size

Platelets are normally very small in size, though occasionally large or giant platelets may be seen. Platelet anisocytosis refers to a significant variation in the size of platelets on a blood film.
  • Look For

  • Large platelets - larger than normal size, though smaller than the size of red cells
  • Giant platelets - larger in size than red blood cells
  • Abnormal Platelet Size
     
  • Causes of Large and Giant Platelets

  • Inherited giant platelet disorders - e.g. Bernard-Soulier
  • Myeloproliferative neoplasms
  • Myelodysplastic syndrome
  • Factitious

Platelet Clumping

In a patient with new or worsening thrombocytopaenia, look for clumping of platelets which would result in a factitiously low platelet count. This is particularly seen at the tail of a blood film.
  • Platelet Clumping
     
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