OVERVIEW
- Prothrombin Time
- Activated Partial Thromboplastin Time
- Thrombin Time
- Fibrinogen
- Fibrin Degradation Products (FDP’s)
- APTT 50% NP
- Retiplase Time
- Euglobin Lysis Time
- Urea solubility Test
PROTHROMBIN TIME
- thromboplastin added
- tests the extrinsic pathway
- ratio compared to control (INR)
- tests factors: I, II, V, VII, X
-> warfarin
-> vitamin K deficiency
-> liver disease
-> DIC
-> artefact: incorrect sampling or increased haematocrit (> 55%)
ACTIVATED PARTIAL THROMBOPLASTIN TIME
- kaolin added
- tests intrinsic pathway
- tests factors: I, II, V, VIII, IX, XI, XII
-> heparin
-> DIC
-> haemophilia
-> liver disease
THROMBIN TIME
- thrombin added to undiluted plasma
- tests the conversion of fibrinogen -> fibrin
- prolonged in:
-> heparin
-> DIC
-> hypofibrinogenaemia
-> fibrin degradation products
FIBRINOGEN
- normal: 1.5-4.0
- high in: acute phase response
- low in:
-> sepsis
-> DIC
FIBRIN DEGRADATION PRODUCTS (FDPs)
- marker of fibrin and fibrinogen breakdown
APTT 50% NP
- mixing of patients sample with pooled normal plasma – 50:50 mix
- failure to correct after mixing:
-> lupus anticoagulant present (should go on to autoantibodies and anti-cardiolipin antibodies)
ECHIS TIME
- snake venom from Echis multisquamatus added to sample
- differentiates liver dysfunction from vitamin deficiency
- this activates prothrombin without requiring vitamin K
- is normal in vitamin K deficiency or warfarin use
- if prolonged:
-> factor deficiency (liver disease)
RETIPLASE TIME
- used to detect deficiency or abnormalities in fibrinogen
- snake venom that has similar action to thrombin but is resistant to inhibition by antithrombin III
- interpret with TCT
- if retiplase time normal and TCT prolonged:
-> heparin
-> hirudin
-> direct thrombin inhibitors
EUGLOBIN LYSIS TIME
- shortened time:
-> presence of systemic fibrinolytic pathway activators
UREA SOLUBILITY TEST
- factor 13 stabilises fibrin
- if deficient 5M urea will dissolve it
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