Coagulation screen Flashcards
What do Prothrombin time (PT) and international normalised ratio (INR) test
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PT measures the time taken for blood to clot in seconds via the extrinsic pathway. INR is the standardised version of this test
what is PT/INR affected by
global reduced clotting factor synthesis (warfarin/vit k deficiency, liver disease)
or increased consumption (DIC)
what is the activated partial thromboplastin time (APTT)
play table tennis inside
it measures the time taken for blood to clot via the intrinsic pathway
what is APTT affected by
warfarin/vit k deficiency, liver disease, DIC (like in extrinsic factor)
anything affecting Factor 8, 9 and 11 (Haemophilia A, B,C and VWD
how does anti-phospholipid syndrome affect APTT
it can cause misleadingly prolonged APTT due to antibody mediated inactivation of the
phospholipid added to activate the intrinsic pathway
what does the bleeding time assess
platelet function. it involves making the pt blled and time how long it takes to stop. only affected by conditions involving platelet function/quality
what conditions increase bleeding time
vWD, thrombocytopenia, TTP, HUS, DIC
what is the thrombin test
. tests how quickly fibrinogen is converted to fibrin by thrombin
other relevant tests in coag screen
FBC (platelet levels), LFT (liver function abnormalities, albumin (livers synthetic function and malnutrition), d-dimer/fibrin degradation products
what does low albumin +high inr (no other cause) suggest
suggests vit k deficiency
vitamin k deficiency/warfarin use coagulation screen results
raised PT/INR and raised APTT because vit K dependent clotting factors are used in intrinsic and extrinsic pathways
haemophilia A/B/C coagulation screen results
raised APTT as factor 8/9/11 used in intrinsic pathway
von willebrands disease coagulation screen results
raised bleeding time as vwF is involved in platelet adhesion. may have increased APTT
normal APTT time
35-45 secs
normal PT/INR time
12-13 secs or 0.8-1.2
