General principles of Hemostasis Flashcards
Two methods of anti-clotting:
cascade inhibition
clot lysis
Membrane protein on platelets that binds collagen:
GP Ia
Membrane protein on collagen that binds vW factor:
GP Ib
Membrane proteins on platelets that bind fibrinogen:
GP IIb-IIIa
Coag pathway with factors all present in blood:
intrinsic
Coag pathway that needs TF from subendothelium:
Extrinsic
Coag cascade triggered by:
Extrinsic pathway – exposed TF
Factors of Intrinsic pathway:
XII(a) –> XI(a) –> IX(a) –> (+ VIII(a)) –> X (start of common pathway)
Factors of Extrinsic pathway:
TF + VIIa –> X(a)–start of common pathway
Cofactor of Xa in common pathway?
Va
Xa does what?
prothrombin –> thrombin
thrombin does what?
inhibits extrinsic and triggers Intrinsic
**fibrinogen—»> FIBRIN = CLOT
Intrinsic cofactor of IXa:
VIIIa
Where does TF come form:
“Hidden cells” exposed during injury
Microparticles floating in blod
Endothelial cells and monocytes
Breaks up clot to form FDPs:
plasmin
how do you get plasmin?
plasminogen + t-PA
Inhibits cofactors VIIIa and Va:
protein C and S
Inhibits A LOT of coag factors?
ATIII
inhibits TF/VIIa complex:
TFPI
Old school way to evaluate platelet response to vascular injury:
Template Bleeding time
Detects platelet function abnormalities:
Platelet aggregation
Why do you put coag tests in a citrate tube?
to get rid of Ca2+
Prothrombin Time (PT) measures?
Extrinsic pathway
**uses thromboplastin in vitro in place of TF
PT used to test:
Factor VII
- made by liver
- needs vit K
- decreased by Coumadin (warfarin)
- SHORT half life
Used instead of PT?
INR
When should you order an INR?
assess liver function
monitor coumadin therapy
diagnose DIC
assess pre-OP status
Partial Thromboplastin Time measures?
Intrinsic pathway
When is PTT increased?
hemophilia A and B
DIC
heparin
inhibitiors?
When to order PTT?
Hx of abnormal bleeding
monitor heparin therapy
dx DIC
dx antiphospholipid antibody
assess pre-OP status
Thrombin time tests?
conversion of fibrinogen to fibrin
**bypasses intrinsic/extrinsic pathways
TT increased?
decreased fibrinogen
or
increased FDPs
Why order a D-Dimer?
rule OUT a clot
VERY sensitive
Adds cross-links to fibrin:
factor XIII
When would you see a decrease in fibrinogen?
DIC
Massive bleed
