Question 1

Unfractionated heparin is commonly monitored by the:&#10;A) PT&#10;B) Partial thromboplastin time (PTT)&#10;C) Thrombin time (TT)&#10;D) Kinetic fibrinogen

Accepted Answer

Unfractionated heparin is commonly monitored by the partial thromboplastin time (PTT), as heparin interferes with the intrinsic pathway of coagulation. PTT measures the amount of time it takes for a clot to form in a blood sample and is used to determine the appropriate dose of heparin to prevent blood clots. PT, thrombin time (TT), and kinetic fibrinogen are not used to monitor unfractionated heparin. PT measures the extrinsic pathway of coagulation and is used to monitor warfarin therapy. TT measures the conversion of fibrinogen to fibrin by thrombin, and kinetic fibrinogen measures the rate of fibrin clot formation.

Question 2

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 = (PT_patient/PT_normal)^ISI (where ISI = international sensitivity index)
What is used for the PT_normal?

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

Accepted Answer

The geometric mean PT for the reference population is used as the PT_normal because it provides a more accurate representation of the typical value, accounting for any outliers or variability in the data. This value is usually established by testing a large number of healthy individuals and calculating the geometric mean of their PT values.

Question 3

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

Chromogenic anti-Xa assay

Accepted Answer

The lupus anticoagulant can interfere with traditional coagulation tests, such as the PTT. Therefore, the chromogenic anti-Xa assay is the preferred method for monitoring heparin therapy in patients with lupus anticoagulant. This assay is not affected by the lupus anticoagulant and provides a more accurate measurement of heparin's anticoagulant effect. The other options (A, B, and D) are not appropriate for monitoring heparin therapy in a patient with lupus anticoagulant.

Question 4

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.

Accepted Answer

Warfarin inhibits the synthesis of vitamin K-dependent coagulation factors (prothrombin, factors VII, IX, and X) and protein C, which is also a vitamin K-dependent protein. Protein C has a shorter half-life than prothrombin and is therefore depleted faster than the procoagulant factors. This leads to a transient hypercoagulable state before full anticoagulation is achieved. In patients with a deficiency of protein C, protein S, or antithrombin, this transient hypercoagulability can predispose them to developing skin necrosis due to thrombosis of small vessels in the skin. Skin necrosis typically occurs within the first 2 to 3 days after starting warfarin therapy.

Question 5

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.

Accepted Answer

Accrediting agencies for clinical laboratories require that the PTT heparin therapeutic range be determined using samples from patients who are receiving heparin therapeutically;they cannot be receiving simultaneous warfarin therapy (thus their PT must be normal).Both a chromogenic anti-Xa assay and PTT are performed on each patient sample,and the paired results are plotted in a linear graph.The range that corresponds to 0.3 to 0.7 chromogenic anti-Xa is the therapeutic range.

Question 6

Why is the platelet count monitored daily for a patient receiving heparin therapeutically?&#10;A) Platelets increase when a patient is overheparinized.&#10;B) Platelets decrease when a patient is overheparinized.&#10;C) A significant decrease in the platelet count is evidence for heparin-induced thrombocytopenia.&#10;D) A significant increase in the platelet count is early evidence for heparin-induced thrombocytosis.

Accepted Answer

Heparin-induced thrombocytopenia (HIT) is a potential complication of heparin therapy, where the body produces antibodies against platelet factor 4 and heparin complexes, leading to platelet destruction and decreased platelet count. Monitoring the platelet count daily can help detect a significant decrease, which is a sign of HIT and requires immediate discontinuation of heparin therapy. Checking for HIT is important as it is associated with an increased risk of thrombosis and other complications.

Question 7

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.

Accepted Answer

The PTT may not accurately reflect the level of anticoagulation in patients who are on heparin therapy or who have coagulation factor deficiencies. In such cases, the chromogenic anti-Xa assay is a better measure of heparin activity. Therefore, the patient should be monitored with the chromogenic anti-Xa assay.

Question 8

All of the following are true about the activated clotting time (ACT) except:&#10;A) It is useful for monitoring warfarin therapy.&#10;B) It can be performed in the clinic or at the patient's bedside.&#10;C) It uses diatomaceous earth as the clot activator.&#10;D) The clinical laboratory scientist inverts the tube until a clot forms.

Accepted Answer

The activated clotting time (ACT) is not useful for monitoring warfarin therapy as it primarily measures the intrinsic pathway of coagulation, while warfarin primarily affects the extrinsic pathway. The other statements are true: the ACT can be performed in the clinic or at the patient's bedside, it uses diatomaceous earth as the clot activator, and the tube is inverted until a clot forms.

Question 9

An INR of 6.5 is obtained on a patient taking warfarin. All quality control is acceptable. What should be done?&#10;A) Report the result.&#10;B) Report only the PT in seconds and ignore the INR.&#10;C) Send an e-mail to the healthcare provider.&#10;D) Call the healthcare provider immediately.

Accepted Answer

An INR of 6.5 is considered an excessively high result and could potentially lead to bleeding risks for the patient. Therefore, it is important to contact the healthcare provider immediately to inform them of the result and to discuss whether any changes to the patient's warfarin therapy should be made.

Question 10

Once a patient is stabilized on warfarin therapy, how often should he or she be monitored?&#10;A) Once every 6 months&#10;B) Once every week&#10;C) Once a year&#10;D) Once a month

Accepted Answer

Patients stabilized on warfarin therapy should be monitored closely with regular blood tests, usually every 4-6 weeks initially and then at least once a month thereafter. This is to ensure that the patient's blood is within the desired therapeutic range and to adjust the dose if necessary. Thus, the best option is D, once a month.

Question 11

Direct thrombin inhibitors include lepirudin and argatroban; they:&#10;A) Require binding to antithrombin to provide their anticoagulant effect&#10;B) Are usually monitored using the PT.&#10;C) Are used when a patient develops heparin-induced thrombocytopenia&#10;D) Bind all serine proteases

Accepted Answer

The answer of Direct thrombin inhibitors include lepirudin and argatroban;...

Question 12

Low-molecular-weight heparin (LMWH):&#10;A) Is essentially as effective therapeutically as unfractionated heparin (UFH)&#10;B) Has the same anti-thrombin effect as UFH&#10;C) Can be monitored using the PTT.&#10;D) Has a shorter in vivo half-life than UFH

Accepted Answer

The answer of Low-molecular-weight heparin (LMWH):&#10;A) Is essentially as effective...

Question 13

Why is it important to monitor patients who are receiving anticoagulant therapy?&#10;A) Drugs are expensive.&#10;B) Prophylactic and therapeutic dosage ranges are unknown.&#10;C) Patients commonly abuse these drugs.&#10;D) Clinical consequences for overdosing or underdosing are significant.

Accepted Answer

The answer of Why is it important to monitor patients...

Question 14

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

Accepted Answer

The answer of Elevated urinary levels of 11-dehydrothromboxane B₂ identify...

Question 15

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 B₂are now easy to perform and widely available.

Accepted Answer

The answer of Which of the following is true related...

Question 16

What anticoagulant therapy is monitored using the ecarin clotting time (ECT)?&#10;A) Unfractionated heparin&#10;B) Warfarin&#10;C) LMWH&#10;D) Direct thrombin inhibitors

Accepted Answer

The answer of What anticoagulant therapy is monitored using the...

Question 17

All of the following serine proteases are bound and inhibited by antithrombin except:&#10;A) Xa&#10;B) IXa&#10;C) VIIa&#10;D) XIa

Accepted Answer

The answer of All of the following serine proteases are...

Deck 46: Monitoring Antithrombotic Therapies