Haemostasis laboratory ( 2 ) Flashcards
What is the purpose of a coagulation screen?
It assesses blood clotting function by testing plasma anticoagulated with trisodium citrate.
Why is trisodium citrate used in coagulation testing?
It chelates calcium, preventing clot formation until testing.
Why is the amount of blood collected important?
Too little blood → excess citrate affects results
Too much blood → insufficient anticoagulant
What are the main coagulation tests?
PT (Prothrombin Time)
APTT (Activated Partial Thromboplastin Time)
D-Dimer
Fibrinogen
Thrombin Time (TT)
What does PT test for?
Issues with extrinsic & common pathways (Factors II, V, VII, X & fibrinogen)
Uses thromboplastin, calcium, tissue factor & phospholipids
What does TT measure?
Conversion of fibrinogen to fibrin using thrombin
What does APTT test for?
Issues with intrinsic & common pathways
Tests Factors XII, XI, IX, VIII, X, V, II
What conditions cause prolonged PT (>16 sec)?
Warfarin therapy
Liver disease
DIC (Disseminated Intravascular Coagulation)
Vitamin K deficiency (Factor VII dependent)
What conditions cause prolonged APTT (>37 sec)?
DIC
Liver disease
Heparin therapy
Factor deficiencies (VIII, IX, XI) → Haemophilia A, B, C
Causes of prolonged TT?
Heparin contamination
Hyperfibrinogenaemia
Dysfibrinogenemia
Why is RT useful?
Similar to TT but not affected by heparin
How is fibrinogen measured?
Clauss method – uses strong thrombin to measure clotting
What do low fibrinogen levels indicate?
Afibrinogenemia – Absent fibrinogen
Hypofibrinogenemia – Persistently low fibrinogen (<1g/L)
Dysfibrinogenemia – Defective fibrinogen
What does prolonged RT indicate?
Afibrinogenemia
Dysfibrinogenemia
Raised fibrin degradation products (FDPs)
What does the D-Dimer test assess?
Breakdown of cross-linked fibrin → Indicates clot formation & breakdown
How does PT affect Warfarin dosage?
Changes in PT → Adjusts Warfarin dose
What is INR used for?
Monitors Warfarin therapy by standardizing PT
