The white cell and the platelet

Question 1

What is leukocytosis?

Answer 1

Increase in the total number of white blood cells in the blood

Question 2

What is included in a white blood cell count?

Give the roles of each

Answer 2

• Neutrophils: ingest and kill bacterial, fungi & cellular debris
• Lymphocytes: produce antibodies for cell-mediated immunity
• Eosinophils: role in allergic reactions, and defence of parasitic infection
• Monocytes: precursor of tissue macrophages
• Basophil: release histamine in inflammatory reactions

Question 3

What are the differentials for neutrophilia?

Answer 3

Neutrophilia is increased number of neutrophils

• Bacterial infection
• Inflammatory reactions
• Disseminated malignancy
• Stress e.g. surgery, burns
• Myeloproliferative conditions
• Corticosteroid therapy

Question 4

What are the differenitals for neutropenia?

Answer 4

Neutropenia is low levels of neutrophils

• Viral infections
• Severe sepsis
• Neutrophil antibodies e.g. SLE
• Bone marrow failure
• Hypersplenism e.g. Felty’s
• Cytotoxic drugs

Question 5

What is the complete absence of circulating neutrophils called?

What can cause it?

Answer 5

Agranulocytosis

Side effect of carbimazole (used to treat hyperthyroidism)

Question 6

What are the differentials for lymphocytosis?

Answer 6

Lymphocytosis is a high number of lymphocytes

• Viral infections
• Chronic infections (TB, hepatitis)
• Myeloproliferative conditions

Remember lymphocytes produce antibodies for cell-mediated immunity

Question 7

What are the differentials for lymphopenia?

Answer 7

Lymphopenia is low levels of lymhocytes

• Bone marrow failure
• Corticosteroid therapy
• SLE
• Uraemia
• HIV infection
• Cytotoxic drugs

Question 8

Describe the mechanism of action of aspirin

Answer 8

• Low dose (75mg) aspirin irreversibly inhibits cyclo-oygenase (cox inhibitor) , preventing conversion of arachidonic acid to endoperoxides such as PGI₂ (platelet aggregators) or TXA₂ (vasoconstrictor and aggregator)
• After administration of the drug, the nuclei of endothelial cells are quickly able to secrete mRNA for PGI2 production
• The anucleate (lacking nucleus) platelets cannot form TXA2, so levels decrease until new platelets are formed in approx 7 days
• Low-dose of aspirin every 24-48 hours thus decrease synthesis of TXA₂ without massively affecting PGI₂ production

Question 9

Define thrombocytopenia

What are the clinical features of thrombocytopenia?

Answer 9

Low platlets

Presentation is with mucocutaneous bleeding:

• Bruising/purpura of the skin
• Epistaxis/menorrhagia

Major haemorrhage is very rare and physical examination is usually normal

Question 10

What are the major causes of thrombocytopenia?

Answer 10

Thrombocytopenia can be due to reduced platelet production in the bone marrow or excessive peripheral destruction of platelets

Reduced production:

• Aplastic anaemia
• Marrow infiltration
• Marrow suppression

Excess destruction:

• Immune thrombocytopenic purpura (ITP)
• Other autoimmune causes:
  
  • SLE
  • Chronic lymphocytic leukaemia (CLL)
  • Viruses
• Thrombotic thrombocytopenic purpura (TTP)
• Haemolytic uraemic syndrome (HUS)
• Sequestration (red blood cells trapped in spleen): hypersplenism