Lab 7 Coagulation Investigations Flashcards
What does aPTT and PT measure?
Measure the time elapsed from activation of coagulation cascade at different points to the generation of fibrin.
What coagulation does PT (prothrombin time) measure and what factors are associated?
Measured extrinsic pathway
Factor 2,5,7,10 involved.
Typically quicker to form clot than intrinsic pathway.
What coagulation does aPPT (activated
partial thromboplastin time) measure and what factors are associated?
Measures intrinsic pathway
Factors 8,9,11,12 involved.
What does prolonged PT indicate?
Factor 2,5,7, or 10 is deficient
What does prolonged aPTT indicate?
Factor 8,9,11,or 12 deficient
Or inhibitor of factors present.
What does TT (thrombin time) measure?
Measures time it takes to form fibrin from fibrinogen in the presence of thrombin.
What does prolonged TT indicate?
Consumptive coagulopathy or Liver disease
What are the function of correction tests?
Used for the investigation of prolonged PT and aPTT.
Used to determine whether prolongation is due to factor deficiency or an inhibitor.
What does shortening of prolonged PT/aPTT time in correction study indicate?
Factor is deficient.
What does no correction or minimal correction of PT/aPTT indicate in correction study?
Inhibitor is present.
What does correction test involve?
Plasma from patient with abnormal PT/aPTT is mixed in equal volume (1:1) with normal pooled plasma
Normal plasma contains all coagulation factor.
If correction study indicates a factor is deficient what is the next step?
Correction of prolonged PT/aPTT
Need to carry out factor assays to determine which factor is deficient.
If correction study indicates an inhibitor is present what is the next step?
No correction of prolonged PT/aPTT
Need to carry out SLE assay to assess presence of inhibitor (La = antiphospholipid antibodies directed against plasma proteins e.g. prothrombin)
Typically involves prolonged aPTT and not PT.
What can occur in individuals with SLE
Higher risk of thrombosis
Paradox because coagulation factors are inhibitied.
Why is quality of blood sample important in coagulation studies?
Coagulation cascade can be prematurely activated when blood is not taken carefully resulting in falsely shortened results.
What ratio does anticoagulant to blood need to be?
1:9
What happens when short draw of blood occurs in coagulation studies.
Anticoagulant to blood ratio 1:9 is not correct leading to false prolonged result
What is the Rosner Index?
Used to see if sample is “corrected” or not by addition of pooled normal plasma
Formula =
aPTT(mix) - aPTT (neat) / initial aPTT of patient
x 100 = ___%
>15% indicates not correction = presence of inhibitor
<15% indicates correction = possible factor deficiency.
What is haemophilia
Blood disorder when factor 8 is missing. (Intrinsic pathway)
prolonged aPTT.
What does <15% Rosner index indicate?
Factor deficiency
Perform factor assay.
What does >15% Rosner index indicate?
Potential inhibitor present
Perform SLE assay.
What treatment should be given to individuals with factor defiencies?
Recombinant factors.
What does a low platelet count and an aPTT >180s indicate?
Sample may be faulty.
Coagulation cascade may have been triggered prematurely.
=> Reject sample and request a fresh sample to redo test.
