18 - Hemostasis and Coagulation Tests Flashcards
how does citrate prevent coagulation?
chelates calcium
which coagulation factor can be deficient without causing a clotting disorder?
XII
which coagulation factor is unique to the extrinsic (“injury”) pathway?
VII
which is more sensitive to common pathway factor deficiencies - PT or PTT?
PT
which factors are vit K dependent?
2 7 9 10
INR is used…
to monitor pts on warfarin
3 broad causes of prolonged PT/PTT
factor deficiency
circulating inhibitor
adsorption of FX by amyloid
work up for prolonged PT/PTT
repeat in optimal conditions
rule out anticoag presence
PT/PTT mixing study
individual factor assays
assay for lupus anticoagulant
purpose of mixing studies in hemostasis labs
allow you to distinguish between lack of factors or presence of inhibitor
lupus anticoagulant (LAC)
not an anticoagulant and not always assoc w/ lupus (great name guys)
interferes w/ phospholipid dependent coag tests like PT/PTT
risk factor for THROMBOSIS
2 tests to determine presence of lupus anticoagulant
DRVVT (dilute Russell’s viper venom test)
hexagnoal phase phospholipid neutralization test
DRVVT
dilute Russell’s viper venom test
used to test for LAC
RVV activates F.X directly. Compare screen and confirmatory conditions (second has more phospholipid to neutalize LAC)
hexagonal phase phospholipid neutralization test
PTT compared to tube w/ added hexagonal phase phosphatidyl ethanolamine which may neutralize LAC
how are specific coagulation factor assays done?
combine pt’s plasma w/ plasma known to be deficient in 1 factor and compare to standard
how is platelet aggregation measured?
light transmission through the sample - more aggregation > more transmission (like an immunoassay)
