Coag Flashcards
what coagulation test assays the extrinsic (factor VII), and the common (factor I, II, V, and X)?
the prothrombin time, PT
when can PT be prolonged without any particular factor deficiency?
warfarin therapy, liver failure, fibrinolysis, DIC
What factors require vitamin K for their synthesis in the liver?
factors II, VII, IX, and X
what can cause vitamin K levels to be decreased?
warfarin (a K antagonist), oral antibiotics, decreased absorption in intestines (maybe obstructive jaundice)
what lab tests will be prolonged in a vit K deficiency?
the PT and aPTT both
what is the INR? what does it use to calculate
the international normalized ratio: the pt’s PT over the geometric mean PT, raised to the ISI of the thromboplastin used (given by manufacturer)
what is an average ref range for a PT?
10 to 14 secs/ Mayo’s is 11.6 to 14.7
Describe the aPTT principle (what 2 components)
First a platelet phospholipid substitute with an activator is added to citrated platelet-poor plasma and incubated; then calcium chloride added. Measures the intrinsic and common systems
what test is used to measure heparin therapy?
the aPTT
aPTT average reference range
23 to 35 seconds
A platelet aggregation study shows abnormal with ristocetin only. What are the possible causes and how would you differentiate?
Both vWD and Bernard-Soulier Syndrome show this pattern. Redoing the ristocetin with added vWF: if corrected, then it is likely vWD; if not, Bernard-Soulier
What disorder affecting platelets will have a platelet aggregation with abnormal results to Epi, ADP, Collagen, and AA but normal with ristocetin?
Glanzmann’s thrombasthenia
what disorder is typified by normal aggregation to ristocetin but abnormal to all other agonists, and is caused by a GPIIb/GPIIIa defect , normal PLT count, abnormal bleeding time, abnormal PFA?
Glanzmann’s
What syndrome exhibits agranular platelets but a normal count? what kind of disorder is this?
Gray PLT syndrome, a storage pool disease with abnormal PLT function due to alpha granule defects
describe the etiology of Heparin induced thrombocytopenia:
patients produce antibodies to Platelet factor 4 bound to heparin in circulation; then the antibody-bound complex (to PF4 and heparin) binds to platelets and the whole shebang is removed by the spleen…hence decreased platelet count
how does heparin work to reduce thrombosis
it binds and enhances the inhibitory activity of antithrombin against serine proteases of the coag system namely factors IIa (thrombin!), IXa and Xa
what does the anti-factor Xa assay help assess?
The anti-factor Xa (anti-Xa) assay is a functional assay that facilitates the measurement of antithrombin (AT)-catalyzed inhibition of factor Xa by unfractionated heparin (UFH) and direct inhibition of factor Xa by low-molecular-weight heparin (LMWH)
what does D-dimer assay measure? how is it useful?
fibrin degradation products, when a fibrin clot has been stabilised by F XIII and is now being lysed. Elevated levels of d-dimer are found in ICF/DIC, DVT, pulmonary embolism, arterial thromboembolism, PREGNANCY, liver disease, chronic hypercoag states…..
what does thrombin time (TT) measure? ref range?
conversion of fibrinogen to fibrin; 10 to 16 secs
