Investigations Flashcards
What part of the coagulation system does Activated Partial Thromboplastin Time (APTT) measure?
The Intrinsic pathway
Which part of the coagulation pathway does prothrombin time (PT) test?
The extrinsic pathway
What are the causes of an increased PT?
Oral anticoagulation therapy (vitamin K antagonists)
Fibrinogen deficiency (factor I)
Prothrombin deficiency (factor II)
Deficiency of factors V, VII or X (in V or X deficiency the activated APTT will be raised as well)
Liver disease, especially obstructive
Vitamin K deficiency
DIC
What are the causes of an increased APTT?
DIC Liver disease Massive blood transfusion Heparin treatment Circulating anticoagulant Modest increase in APTT in pts taking oral anticoagulants Haemophilia
What factors in the coagulation pathway affect thrombin clotting time?
Concentration of factor I, and the presence of fibrin or fibrinogen degradation products and heparin
What causes an increased thrombin clotting time?
DIC
Increased fibrin degradation products (FDPs)/cross-linked fibrin degradation products (XDPs)/D-dimers
Heparin
Dysfibrinogenaemia (inherited, mutation in fibrinogen gene leads to amino acid change and non-functional fibrinogen)
What role in the coagulation pathway do antithrombin and proteins C&S play?
Natural anticoagulants - deficiencies may lead to thromboembolic disease
What are the causes of low antithrombin levels?
Hereditary (40-60% normal level), autosomal dominant Chronic liver disease Protein wasting disorders Heparin therapy 3rd trimester of pregnancy Acute leukaemia Bruns Renal disease Gram -ve sepsis
What are the causes of low levels of Protein S?
Inherited (autosomal dominant) Pregnancy Oral anticoagulants, e.g. warfarin Nephrotic syndrome Liver disease
What are the causes of low levels of Protein C?
Hereditary (autosomal dominant) Liver disease Malignancy Warfarin therapy Pregnancy
