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Hemostasis lab tests
Lab tests for hemostatic factors
20
Physiology
Graduate
09/09/2012

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Term
aPTT
Definition
adjusted partial thromboplastin time
-measures INTRINSIC pathway
"How long does plasma clot when I expoe it to Ca2+ and (-) charged surfaces?"
Process: Add PL, Ca2+, and activating surface (glass), add CaCl2, measure time to clot
Term
PT
Definition
prothrombin time
-measures EXTRINSIC pathway
"How long does plasma clot when I expose it to tissue factor (TF, aka thromboplastin)?"
Process: Incubate plasma+TF (thromboplastin), add CaCl2, measure time to clot
Term
TT
Definition
thrombin time
-measures quality of fibrinogen
If normal PTT and normal TT, the problem is in the intrinsic pathway
Process: plasma+thrombin+Ca2+; measure how long it takes for fibrinogen to convert to fibrin and form a clot
Term
D dimers
Definition
Great lab value for DIC, DVT/PE
product of fibrinolysis of cross-linked fibrinogen by plasmin
Term
Citrate plasma
Definition
9:1 plasma:citrate ratio
-citrate chelates Ca2+ to stop clot formation before testing
Term
INRhttp://www.flashcardmachine.com/my-flashcards/quick-editor.cgi#
Definition
patient PT/mean normal PT (prothrombin time)
-standardize PT results
Term
Ddx for: High PTT, normal PT, normal platelets
Definition
Hemophilia (factor VIII or IX)
Deficiencies/inhib of intrinsic pathway
vWD
Heparin
HMWK deficiency (normally activates XII)
Term
Ddx for: normal PTT, High PT, normal platelets
Definition
Factor VII deficiency
Warfarin reaction
Term
Ddx for: high PTT, high PT, normal platelets
Definition
Vit K deficiency
II, IV, X deficiency/inhibition (common pathway)
Lack of fibrinogen
Term
Ddx for: high PTT, high PT, low platelets
Definition
DIC
liver disease
Term
Ddx for normal PTT, PT, and platelets
Definition
Consider Factor XIII deficiency
Term
Mixing studies help you determine what? Talk about the two types of mixing studies?
Definition
Determine deficiency (1:1 ratio of pt/normal --> normal clotting time) VS. inhibition (1:1 ratio --> normal clotting time)

-Immediate mix: check for lupus anticoagulant (fast-acting inhib)
Term
Immediate mix study
Definition
aPTT (measure intrinsic pathway) performed immediately after mixing pt and normal plasma
-Check for evidence of lupus anticoagulant - fast acting inhibitor
Term
Delayed (incubated) mix study
Definition
aPTT performed after letting mixture incubate for 1 hr
-needed to distinguish b/n factor deficiency and time-dep inhib (like factor VIII inhib)
Term
Factor assays
Definition
Determine levels of coagulation cascade factors
Term
Factor inhibitor titers
Definition
look for presence of high titer factor inhibitors
Term
Monitor anti-thrombotic therapies
Definition
1)coumadin (warfarin) (causes production of functionally-deficient Vit K-dep ptns II, VII, IX, X, C, S) - monitor using PT/INR
-measure using anti-Xa if lupus anticoagulant is present

2)Heparin - monitor using aPTT, TT, anti-Xa, activated whole blood clotting time
3)Low MW heparin - anti-Xa assay
4) Direct thrombin inhib - TT
Term
Platelet testing techniques?
Definition
-peripheral smear
-platelet count
-template bleeding time
-platelet aggregation studies
-epinephrine
-collagen
-ADP
-Arachidonic Acid
-Ristocetin
Term
Ristocetin aggregation
Definition
Test for Bernard-Soullier syndrome
-requires GP1b and vWf for aggregation
-if absent, no aggregation
Term
SRA (serotonin release assay)
Definition
Gold standard for Dx HIT (heparin-induced thrombocytopenia)
-serotonin is in delta granules, is a marker for platelet activation
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