Coag

Question 1

what coagulation test assays the extrinsic (factor VII), and the common (factor I, II, V, and X)?

Answer 1

the prothrombin time, PT

Question 2

when can PT be prolonged without any particular factor deficiency?

Answer 2

warfarin therapy, liver failure, fibrinolysis, DIC

Question 3

What factors require vitamin K for their synthesis in the liver?

Answer 3

factors II, VII, IX, and X

Question 4

what can cause vitamin K levels to be decreased?

Answer 4

warfarin (a K antagonist), oral antibiotics, decreased absorption in intestines (maybe obstructive jaundice)

Question 5

what lab tests will be prolonged in a vit K deficiency?

Answer 5

the PT and aPTT both

Question 6

what is the INR? what does it use to calculate

Answer 6

the international normalized ratio: the pt’s PT over the geometric mean PT, raised to the ISI of the thromboplastin used (given by manufacturer)

Question 7

what is an average ref range for a PT?

Answer 7

10 to 14 secs/ Mayo’s is 11.6 to 14.7

Question 8

Describe the aPTT principle (what 2 components)

Answer 8

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

Question 9

what test is used to measure heparin therapy?

Answer 9

the aPTT

Question 10

aPTT average reference range

Answer 10

23 to 35 seconds

Question 11

A platelet aggregation study shows abnormal with ristocetin only. What are the possible causes and how would you differentiate?

Answer 11

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

Question 12

What disorder affecting platelets will have a platelet aggregation with abnormal results to Epi, ADP, Collagen, and AA but normal with ristocetin?

Answer 12

Glanzmann’s thrombasthenia

Question 13

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?

Answer 13

Glanzmann’s

Question 14

What syndrome exhibits agranular platelets but a normal count? what kind of disorder is this?

Answer 14

Gray PLT syndrome, a storage pool disease with abnormal PLT function due to alpha granule defects

Question 15

describe the etiology of Heparin induced thrombocytopenia:

Answer 15

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

Question 16

how does heparin work to reduce thrombosis

Answer 16

it binds and enhances the inhibitory activity of antithrombin against serine proteases of the coag system namely factors IIa (thrombin!), IXa and Xa

Question 17

what does the anti-factor Xa assay help assess?

Answer 17

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)

Question 18

what does D-dimer assay measure? how is it useful?

Answer 18

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…..

Question 19

what does thrombin time (TT) measure? ref range?

Answer 19

conversion of fibrinogen to fibrin; 10 to 16 secs