Deck 43: Antithrombotic Therapies and their Laboratory Assessment

Question 1

After confirmation of a deep vein thrombosis (DVT)and pulmonary embolus in a patient,a baseline coagulation screen and platelet count are obtained.His fibrinogen is 620 mg/dL.When the PTT is performed at 6 hours after initiation of therapy,it is 45 seconds (reference range,25 to 37 seconds).What should be done?

A)Report the PTT as not responding.
B)Monitor the patient with the chromogenic anti-Xa assay.
C)Add an additional standard amount of heparin to the patient plasma to improve the sensitivity.
D)Add a standard amount of antithrombin to the patient plasma to improve the sensitivity.

Answer 1

Monitor the patient with the chromogenic anti-Xa assay.

Question 2

An INR of 6.5 is obtained on a patient taking warfarin.All quality control is acceptable.What should be done?

A)Report the result.
B)Report only the PT in seconds and ignore the INR.
C)Send an e-mail to the healthcare provider.
D)Call the healthcare provider immediately.

Answer 2

Call the healthcare provider immediately.

Question 3

What anticoagulant therapy is monitored using the ecarin clotting time (ECT)?

A)unfractionated heparin
B)warfarin
C)LMWH
D)direct thrombin inhibitors

Answer 3

direct thrombin inhibitors

Question 4

All of the following serine proteases are bound and inhibited by antithrombin except

A)Xa
B)IXa
C)VIIa
D)XIa

Question 5

Low-molecular-weight heparin (LMWH)

A)is essentially as effective therapeutically as unfractionated heparin (UFH).
B)has the same antithrombin effect as UFH.
C)can be monitored using the PTT.
D)has a shorter in vivo half-life than UFH.

Question 6

All of the following are true about the activated clotting time (ACT)except

A)it is useful for monitoring warfarin therapy.
B)it can be performed in the clinic or at the patient's bedside.
C)it uses diatomaceous earth as the clot activator.
D)the clinical laboratory scientist inverts the tube until a clot forms.

Question 7

Direct thrombin inhibitors include lepirudin and argatroban;they

A)require binding to antithrombin to provide their anticoagulant effect.
B)are usually monitored using the PT.
C)are used when a patient develops heparin-induced thrombocytopenia.
D)bind all serine proteases.

Question 8

Why is the platelet count monitored daily for a patient receiving heparin therapeutically?

A)Platelets increase when a patient is overheparinized.
B)Platelets decrease when a patient is overheparinized.
C)A significant decrease in the platelet count is evidence for heparin-induced thrombocytopenia.
D)A significant increase in the platelet count is early evidence for heparin-induced thrombocytosis.

Question 9

Which of the following is true related to the use of aspirin to prevent cardiovascular disease?

A)It is used to prevent arterial thrombosis.
B)New studies show it is not effective.
C)It works well but must be carefully monitored with monthly bleeding times.
D)Aspirin monitoring tests such as thromboxane B2 are now easy to perform and widely available.

Question 10

A patient is admitted through the hospital emergency department with thrombosis,and heparin is initially begun.Her baseline PTT,before heparin therapy,is prolonged at 68 seconds.Further laboratory studies determine that she has the lupus anticoagulant.What test should be used to monitor her heparin therapy?

A)PTT
B)PTT after first adding antithrombin to her plasma
C)chromogenic anti-Xa assay
D)TT after first making a 1:10 dilution of the patient plasma

Question 11

A patient is stabilized on warfarin therapy and being monitored using the prothrombin time (PT)followed by calculation of the international normalized ratio (INR).The formula for calculating the INR is:
INR = (PTₚₐₜᵢₑₙₜ/PTₙₒᵣₘₐₗ)ᴵˢᴵ (where ISI = international sensitivity index)
What is used for the PTₙₒᵣₘₐₗ?

A)arithmetic mean PT for the control
B)geometric mean PT for the reference population
C)arithmetic mean PT as found in a standard reference textbook
D)geometric mean PT reported by the manufacturer of the PT reagent being used

Question 12

Unfractionated heparin is commonly monitored by the

A)PT.
B)partial thromboplastin time (PTT).
C)thrombin time (TT).
D)kinetic fibrinogen.

Question 13

A clinical laboratory receives a new lot of PTT reagent,so clinical laboratory scientists in the laboratory need to establish the heparin therapeutic range for this new reagent lot.How should this be done?

A)Compare PTT results for patient heparinized samples to those for the lot of PTT reagent that is presently being used.
B)Perform chromogenic Xa and PTT assays on patient heparinized samples, and do a statistical analysis of result comparisons.
C)Add heparin at various therapeutic concentrations to normal plasma, and perform PTT on each concentration using the new lot of reagent.
D)Add heparin at high concentration to one normal plasma, make dilutions of this plasma, and then perform PTT on each diluted sample using the new lot of reagent.

Question 14

Once a patient is stabilized on warfarin therapy,how often should he or she be monitored?

A)once every 6 months
B)once every week
C)once a year
D)once a month

Question 15

Elevated urinary levels of 11-dehydrothromboxane B₂ identify patients who are

A)at risk for heparin-induced thrombocytopenia.
B)overanticoagulated with warfarin.
C)resistant to aspirin antiplatelet therapy.
D)resistant to direct thrombin inhibitors.

Question 16

Warfarin skin necrosis occurs within the first 2 to 3 days after starting warfarin therapy because

A)the platelet count decreases to fewer than 100 * 109/L, and significant bleeding occurs.
B)protein C decreases significantly before full anticoagulation, and skin thrombosis results.
C)prothrombin decreases rapidly generating less thrombin, and significant bleeding occurs.
D)plasminogen increases, and rapid clot lysis occurs.

Question 17

Why is it important to monitor patients who are receiving anticoagulant therapy?

A)Drugs are expensive.
B)Prophylactic and therapeutic dosage ranges are unknown.
C)Patients commonly abuse these drugs.
D)Clinical consequences for overdosing or underdosing are significant.