Haemostasis 3 Flashcards
What does Prothrombin Time measure (PT)?
Extrinsic = VII
Common pathway = X, VI, II (prothrombin) and I (fibrinogen)
What does the activated partial prothrombin time (APPT) measure?
Intrinsic pathway = XII, Xi, IX and VIII
Common pathway = X, V, II (prothrombin) and I (fibrinogen)
What does the thrombin clotting time and Fibrinogen assay (TCT) measure?
I (Fibrinogen)
What is the International Normalized Ratio (INR)?
Standardized commercial PT test results.
Ratio of patients PT to PT of normal plasma
What is the reference range for the INR?
0.8-1.2
What do coagulation assays measure?
Measured as a percentage of normal clotting activity - except fibrinogen
List some causes of prolonged bleeding.
Defective vessel wall disorders
Platelet disorders (thrombocytopenia, defective platelet function)
Von Willebrand disease (low levels/abnormal vWF molecules, reduced platelet aggregation and prolonged bleeding)
Defective coagulation
How do we assess bleeding disorders?
History - location of bleeding, pattern of bleeding, drug history and diet, family history
What would be the lab assessments for bleeding disorders?
Blood screen - platelet count and morphology
Coagulation screen - PT, APTT, fibrinogen (TCT)
Second stage tests - vW factor assays, platelet function studies, coagulation factor assays
What is Disseminated Intravascular Coagulation?
Widespread activation of platelets and coagulation in blood.
What are the pathological processes behind DIC?
Release of procoagulant material into the circulation
Widespread focal or diffuse damage to endothelial cells
What happens in mild DIC?
No adverse effects
What happens in moderate/severe DIC?
Bleeding
and or
Thromboses and ischaemia
Describe what happens in DIC.
Tissue factor/other cell products released in blood vessels or any cause of extensive endothelial cell damage Resulting in: - platelet activation and aggregation - activation of coagulation - formation of micro thrombi - secondary activation of fibrinolysis
NB: fibrinolysis is always activated in DIC
Fibrin is cleared from the small blood vessels: high FDP levels produced
Inadequate activation results in microvascular thromboses
What are the clinical findings of DIC?
Variable - those of the underlying condition
Bleeding and/or microvascular thromboses present if DIC is moderate/severe
What the laboratory findings of DIC (consumptive coagulopathy)?
Falling fibrinogen concentration - prolonged TCT
Falling platelet count
High/rising level of fibrin degradation products (FDPs)
Reduced coagulation factors
What diseases can cause DIC?
Gram negative septicaemia
How do we treat DIC?
Treat the cause and DIC will stop: - infection = antibiotics - trauma/shock = treat trauma/shock Secondary bleeding caused by DIC: - replace with blood transfusion therapy
What other disorders can cause DIC?
Any severe/widespread tissue injury - prolonged shock - extensive tissue trauma - severe burns - severe viral infections Traumatic brain injury with brain myelin (lipid) released into blood = activates platelets and coagulation
What is the INR used for monitoring?
Warfarin coagulation
What does a lack of vit K result in and why?
Lack of vitamin K results in bleeding
Factors II, VII, IX and X do not function normally
What are common conditions causing vit K deficiency?
Liver disease
Newborn infants
Small bowel malabsorption disorders
What is vit K?
Fat soluble vitamin
- vegetable sources and bacterial synthesis in colon
