Question 1

Unfractionated heparin is commonly monitored by the:

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?

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?

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:

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?

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?

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?

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:

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?

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?

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:

Accepted Answer

Direct thrombin inhibitors, such as lepirudin and argatroban, are often used when a patient develops heparin-induced thrombocytopenia (HIT). They do not require binding to antithrombin to provide their anticoagulant effect and they do not bind all serine proteases. They are not usually monitored using the PT (prothrombin time), but rather the aPTT (activated partial thromboplastin time).

Question 12

Low-molecular-weight heparin (LMWH):

Accepted Answer

Low-molecular-weight heparin (LMWH) is essentially as effective therapeutically as unfractionated heparin (UFH). LMWH has a more predictable anticoagulant response, allowing for fixed dosing without the need for routine monitoring using the PTT, unlike UFH. Additionally, LMWH has a longer in vivo half-life compared to UFH, which contributes to its dosing advantages.

Question 13

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

Accepted Answer

Monitoring patients who are receiving anticoagulant therapy is important because clinical consequences for overdosing or underdosing are significant. Anticoagulant therapy helps prevent blood clots, but if the dosage is too low, clot formation can still occur and if the dosage is too high, bleeding can occur. Therefore, monitoring the patient's blood clotting ability is crucial to ensure that the dosage is appropriate for the patient's needs.

Question 14

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

Accepted Answer

Elevated urinary levels of 11-dehydrothromboxane B2 (11-dTXB2) indicate resistance to aspirin antiplatelet therapy.

Question 15

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

Accepted Answer

Aspirin is commonly used to prevent arterial thrombosis, which can lead to cardiovascular disease. There is no evidence to suggest that new studies have found aspirin to be ineffective, and while monitoring bleeding times is important in some cases, it is not necessary for all patients. There is no clear mention of a specific aspirin monitoring test being widely available.

Question 16

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

Accepted Answer

The ecarin clotting time (ECT) is a specific diagnostic test used to monitor the anticoagulant effect of direct thrombin inhibitors such as dabigatran. Therefore, the correct choice is D. Unfractionated heparin and LMWH are typically monitored using the activated partial thromboplastin time (aPTT) or anti-factor Xa assay. Warfarin is monitored using the international normalized ratio (INR).

Question 17

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

Accepted Answer

Antithrombin inhibits thrombin (IIa), factor Xa, factor IXa, and factor XIa. However, it does not inhibit factor VIIa, so the correct answer is C.

Quiz 46: Monitoring Antithrombotic Therapies

Unfractionated heparin is commonly monitored by the:

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

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?

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

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

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

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

Direct thrombin inhibitors include lepirudin and argatroban; they:

Low-molecular-weight heparin (LMWH) :

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

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

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

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

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

Quiz 46: Monitoring Antithrombotic Therapies

Unfractionated heparin is commonly monitored by the:

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

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?

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

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

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

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

Direct thrombin inhibitors include lepirudin and argatroban; they:

Low-molecular-weight heparin (LMWH) :

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

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

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

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

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

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