Unit 2: Coagulation disorders
Applied Haematology-II notes · PTU syllabus (BMLS601-18)
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Unit summary
Bleeding and clotting disorders need careful laboratory work-up. This unit covers normal fibrinolysis and hyperfibrinolysis, DIC, haemophilia and von Willebrand disease, ITP, and platelet function tests.
After this unit you can
- Explain fibrinolysis and diagnose hyperfibrinolysis
- Diagnose DIC
- Diagnose haemophilia, von Willebrand disease and ITP
- Perform and interpret platelet function tests
PTU syllabus topics
- Mechanism of normal fibrinolysis and laboratory diagnosis of hyperfibrinolysis
- mechanism and diagnosis of disseminated intravascular coagulation (DIC)
- laboratory diagnosis of haemophilia and von Willebrand disease
- laboratory diagnosis of idiopathic thrombocytopenic purpura (ITP)
- platelet function tests and interpretation
Haemophilia A or B
Normal / prolonged
Normal
von Willebrand disease
Normal / normal or prolonged
Normal count; poor function, long bleeding time
DIC
Prolonged / prolonged
Low; D-dimer high, fibrinogen low
ITP
Normal / normal
Low
Topic 1
Normal fibrinolysis and hyperfibrinolysis
- 1Endothelium releases tissue plasminogen activator (tPA)
- 2tPA converts plasminogen to plasmin on fibrin
- 3Plasmin digests fibrin into fibrin degradation products (FDPs) and D-dimer
- 4Inhibitors: plasminogen activator inhibitor-1, α2-antiplasmin
- Hyperfibrinolysis: excessive plasmin activity — after prostate surgery, liver disease, thrombolytic therapy. Lab: short euglobulin clot lysis time, low fibrinogen, high FDPs; thromboelastography shows early lysis.
Topic 2
Disseminated intravascular coagulation (DIC)
- Widespread activation of clotting consumes platelets and factors while microthrombi form, followed by bleeding. Causes: sepsis, obstetric complications (abruptio placentae, amniotic fluid embolism), trauma, snakebite, acute promyelocytic leukaemia.
- Platelets
- Low and falling
- PT and APTT
- Prolonged
- Fibrinogen
- Low
- D-dimer and FDPs
- Markedly raised
- Smear
- Schistocytes
- Scoring
- ISTH DIC score combines these
Topic 3
Haemophilia and von Willebrand disease
Inheritance
X-linked recessive (males affected)
Autosomal (usually dominant)
Defect
Factor VIII (A) or IX (B) deficiency
Low or abnormal vWF (and secondary low VIII)
Bleeding
Joints and muscles (haemarthroses)
Mucosal — nose, gums, heavy periods
Tests
Prolonged APTT; normal PT, platelet count and BT; low factor VIII or IX
Prolonged BT and PFA-100; APTT normal or prolonged; low vWF antigen, low ristocetin cofactor activity; abnormal ristocetin aggregation
Topic 4
Idiopathic (immune) thrombocytopenic purpura (ITP)
- Autoantibodies against platelets cause destruction in the spleen. Acute ITP: children after viral infection, usually self-limiting; chronic ITP: adults, mostly women.
- Platelet count
- Low (often below 20,000/µL)
- Smear
- Large platelets; otherwise normal cells
- Coagulation
- PT and APTT normal
- Marrow
- Normal or increased megakaryocytes
- Diagnosis
- Of exclusion — rule out drugs, HIV, hepatitis C, SLE, leukaemia
Topic 5
Platelet function tests
Bleeding time
In vivo platelet plug
Prolonged in platelet and vWF disorders
Clot retraction
Clot shrinks within 1 hour as platelets contract
Poor in thrombocytopenia and Glanzmann thrombasthenia
Platelet aggregation (light transmission aggregometry)
Platelet-rich plasma with agonists (ADP, collagen, adrenaline, arachidonic acid, ristocetin)
Absent with all except ristocetin in Glanzmann; absent with ristocetin in Bernard–Soulier and vWD; aspirin abolishes arachidonic acid response
Platelet adhesion (glass bead retention)
Platelets adhere to glass
Reduced in vWD
Prothrombin consumption index
Serum prothrombin left after clotting
High residual prothrombin in platelet defects
PFA-100
Closure time through a coated membrane
Screening for vWD and aspirin effect
Platelet factor 3 availability
Procoagulant phospholipid activity
Reduced in some platelet disorders
Key terms
- Plasmin
- Enzyme digesting fibrin
- D-dimer
- Fibrin breakdown product indicating clot formation and lysis
- DIC
- Consumptive coagulopathy with clotting and bleeding
- von Willebrand factor
- Protein mediating platelet adhesion and carrying factor VIII
- Platelet aggregometry
- Measuring platelet clumping with agonists
Quick revision
- tPA, plasmin, FDPs, D-dimer; hyperfibrinolysis tests.
- DIC causes and lab findings.
- Haemophilia A and B vs vWD; inheritance, bleeding pattern, tests.
- ITP: isolated thrombocytopenia, normal coagulation, exclusion diagnosis.
- Bleeding time, clot retraction, aggregation patterns, adhesion, PCI, PFA-100.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.What is D-dimer?
- Q2.Give four laboratory findings in DIC.
- Q3.How is haemophilia inherited?
- Q4.Which test distinguishes haemophilia A from B?
- Q5.What platelet aggregation pattern occurs in Glanzmann thrombasthenia?
- Q6.Why is ITP a diagnosis of exclusion?
Long-answer questions
- Q1.Explain fibrinolysis and the laboratory diagnosis of hyperfibrinolysis and DIC.
- Q2.Describe the laboratory diagnosis of haemophilia and von Willebrand disease.
- Q3.Describe ITP and platelet function tests.
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