Coagulation Flashcards
What molecule acts to link platelets to exposed collagen?
von Willebrand factor
What are the major two compounds released by platelets upon activation?
ADP and Thromboxane A2
What sample tube are coagulation samples collected in? What do these vials contain? What is the proper ratio of sample: this compound?
Blue topped- contain citrate; 9:1
On what kind of sample are coagulation tests performed?
Plasma
What is the difference between plasma and serum?
Serum contains very little coagulation factor and complement because there is no anticoagulant added
How is the intrinsic coagulation pathway tested?
Activated partial thrombolastin time (aPTT)
What is the initial step of the intrinsic coagulation cascade?
Trauma to vessels exposes blood to collagen and factor XII is activated
What is the function of FVa and what other factor is required for this action?
Converts prothrombin to thrombin with the aid of FVa
What is the action of thrombin (IIa) in the coagulation cascade?
Cleavage of fibrinogen to fibrin
How is the extrinisic pathway clinically tested?
Prothrombin time (PT)
What is the initiating step of the intrinsic pathway of coagulation?
Trauma to vascular wall or extravascular tissue exposes Tissue Factor (III) which forms a complex with FVII, activating FVII
What is the action of the TF-FVIIa complex?
Activation of X to Xa
What is the normal PT range?
12-15 sec
What clinical coagulation tests will be abnormal in a patient with an extrinsic pathway deficiency?
Prolonged PT time only
What clinical coagulation tests will be abnormal in a patient with an intrinsic pathway deficiency?
Prolonged aPTT
What clinical coagulation tests will be abnormal in a patient with an common pathway deficiency?
Prolonged PT and aPTT
A Vit. K deficiency would decrease the synthesis of which coagulation cascade factors?
II, VII, IX, and X
Approximately what percent of a normal level of a coagulation factor is generally sufficient to yield a normal PT or aPTT?
20-40%
What is a mixing study?
The mixing of a normal plasma sample with a deficient sample to access PT
In what case would adding a factor through a mixing study not correct a prolonged clotting time?
If the prolonged result is due to an inhibitor
If a mixing test is immediately abnormal what does it indicate? If the mixing study immediately results in a normal time, but later points show abnormality, what does it indicate?
Immediately abnormal= heparin or lupus inhibitor; Later abnormal= antibody inhibitor to clotting factor
What is the normal range for PTT?
25-36 seconds
What is Lupus anticoagulant?
LAC interferes with phospholipid-dependent coagultion tests like PT and PTT
What two assays are performed for lupus anti-coagulant?
Dilute Russell’s viper venom test (DRVVT) and Hexagonal phase phospholipid neutralization test
