Question 1

A prolonged PTT is corrected when mixed with normal plasma and tested immediately and after a 2-hour incubation. Which test (or tests) should be performed next?

Accepted Answer

A prolonged PTT that corrects upon mixing with normal plasma suggests a deficiency in a clotting factor. To identify which factor is deficient, factor VIII and IX assays should be performed. The Bethesda titer is used to detect inhibitors to clotting factors, high phospholipid PTT is used to evaluate lupus anticoagulant, and anti-Xa assay is used to monitor heparin therapy. None of these tests are indicated in this particular scenario.

Question 2

A patient's platelet count drops 4 days after being placed on heparin. Select the correct interpretation.

Accepted Answer

A drop in platelet count after initiation of heparin therapy can be a sign of heparin-induced thrombocytopenia (HIT), which is a potentially serious adverse reaction that requires prompt intervention. However, there are also benign, limited forms of thrombocytopenia that can occur with heparin use. To differentiate between HIT and benign thrombocytopenia, an immunoassay for heparin-dependent anti-platelet factor 4 (PF4) antibodies is recommended. Performing a bleeding time or evaluating for qualitative platelet disorders would not be sufficient to distinguish between these two conditions.

Question 3

Which of the following is an acceptable sample for testing on a photo-optical clot-detecting instrument?

Accepted Answer

Plasma collected using a 9:1 ratio of whole blood to 3.2% sodium citrate is the recommended sample for testing on a photo-optical clot-detecting instrument as it contains an anticoagulant (sodium citrate) that prevents clot formation during the test. Lipemic plasma and hemolyzed plasma can interfere with the accuracy of the test results, while serum does not contain the necessary anticoagulant.

Question 4

Which of the following would likely have a normal PT?

Accepted Answer

Factor VIII deficiency affects the intrinsic pathway, which is measured by the activated partial thromboplastin time (aPTT), not the prothrombin time (PT). PT measures the extrinsic and common pathways of coagulation.

Question 5

A patient sample has normal platelet aggregation patterns for all agonists except that no reaction occurs with ristocetin. Ristocetin agglutination is not corrected with exogenous VWF. What condition is most likely?

Accepted Answer

The lack of platelet aggregation with ristocetin and the fact that exogenous VWF does not correct the agglutination suggests a deficiency or dysfunction of the platelet GPIb-V-IX receptor, which is a characteristic of Bernard-Soulier syndrome. VWD, storage pool disorders, and aspirin use would not specifically affect the platelet response to ristocetin.

Question 6

Patients with which of the following would have a normal PT?

Accepted Answer

Factor IX deficiency, also known as Hemophilia B or Christmas disease, primarily affects the intrinsic pathway of the coagulation cascade. Prothrombin time (PT) measures the extrinsic and common pathways, which are not directly affected by Factor IX deficiency. Therefore, patients with Factor IX deficiency would have a normal PT but an abnormal activated partial thromboplastin time (aPTT).

Question 7

The bleeding time result will be normal and thus of no value to perform in patients who have:

Accepted Answer

Bleeding time primarily assesses platelet function and the initial phase of clot formation, not specific clotting factors like Factor VIII. Factor VIII deficiency, as seen in Hemophilia A, affects the intrinsic coagulation pathway and would not typically alter bleeding time results.

Question 8

Which of the following will cause spuriously prolonged clot-based coagulation tests?

Accepted Answer

An evacuated 3.2% sodium citrate tube filled to 50% capacity will have an incorrect blood-to-anticoagulant ratio, leading to spuriously prolonged clot-based coagulation tests.

Question 9

How often must the partial thromboplastin time (PTT) reference interval be determined?

Accepted Answer

The PTT reference interval should be determined with each new lot of reagent to ensure that the reagent is not affecting the results.

Question 10

A platelet aggregation study shows diminished response to all agonists except for a small response to arachidonic acid and full response to ristocetin. Which condition is most likely?

Accepted Answer

Glanzmann thrombasthenia is characterized by a diminished response to all agonists except for a normal response to ristocetin, which matches the description given. This condition is due to a deficiency or dysfunction of the platelet glycoprotein IIb/IIIa complex, which is crucial for platelet aggregation.

Question 11

Which of the following is an acceptable sample for a prothrombin time (PT) test?

Accepted Answer

The answer of Which of the following is an acceptable...

Question 12

A patient admitted to the hospital with thrombosis is given the standard heparin dosage. Twenty-four hours after the heparin is started, the PTT is 38 seconds (reference range, 25 to 37 seconds). Both normal and abnormal controls are within their limits. Which of the following is most likely?

Accepted Answer

A prolonged PTT can be a sign of inadequate anticoagulation therapy. If both normal and abnormal controls are within their limits, a laboratory error is unlikely. Heparin-induced thrombocytopenia is associated with a decrease in platelet count, but this information is not provided in the question stem. Switching to LMWH may be considered, but the question stem does not provide enough information to make this determination. Low antithrombin levels can lead to a higher heparin requirement, resulting in a longer PTT despite standard dosing.

Question 13

A patient is stabilized on warfarin with an international normalized ratio (INR) of 2.7. He develops pneumonia and is admitted to the hospital. His appetite is depressed and he is placed on broad-spectrum antibiotic agents. At 1 week after the admission, his INR is 5.0. What is the most likely interpretation?

Accepted Answer

The most likely interpretation of the elevated INR is that the patient's vitamin K levels have been reduced, either due to the pneumonia or antibiotic treatment, leading to increased effects of warfarin. The patient should be given vitamin K to reverse the anticoagulant effects of warfarin. Giving more warfarin or ruling out heparin administration is unlikely to be helpful in this situation. A clotted specimen is also unlikely given the circumstances.

Question 14

Which of the following is necessary for normal platelet aggregation?

Accepted Answer

The answer of Which of the following is necessary for...

Question 15

How often must controls be run for the PT and PTT?

Accepted Answer

Controls for PT (Prothrombin Time) and PTT (Partial Thromboplastin Time) tests must be run at least once per 8-hour shift to ensure the accuracy and reliability of the testing process. This frequency ensures that the testing system is consistently performing as expected throughout the day.

Question 16

What is the test commonly used to monitor the high heparin doses used in cardiac bypass surgery?

Accepted Answer

PTT (partial thromboplastin time) is the test commonly used to monitor the high heparin doses used in cardiac bypass surgery. Heparin is an anticoagulant that prevents blood clots from forming during surgery. PTT measures the time it takes for blood to clot and is used to adjust the heparin dosage during surgery to maintain an appropriate level of anticoagulation. Prothrombin time (PT) measures the time it takes for blood to clot and is used to monitor warfarin therapy (a different type of anticoagulant). Thrombin clotting time and fibrinogen levels are not commonly used to monitor heparin therapy in cardiac bypass surgery.

Question 17

Which of the following is good practice in regard to phlebotomy on patients with hemostasis testing ordered?

Accepted Answer

Using a 20- or 21-gauge needle is recommended for phlebotomy, especially for hemostasis testing, to ensure adequate blood flow and minimize the risk of hemolysis or clotting within the collection tube.

Question 18

Which of the following is acceptable practice regarding collection of blood when using a syringe and winged needle set?

Accepted Answer

Evacuated tubes must be placed in a rack when filling to prevent breakage and to ensure proper mixing of additives. Option A is not acceptable practice as blood collected in a syringe should be transferred to the appropriate tubes at the time of collection. Option C is not a requirement unless specific testing guidelines indicate the need for discarding the first portion of the blood collected. Option D is not acceptable practice as it can cause hemolysis and contamination of the sample.

Question 19

Which of the following conditions would have a normal PTT?

Accepted Answer

Factor VII is not involved in the intrinsic pathway, which is measured by PTT. Lupus anticoagulant and heparin therapy prolong PTT, while fibrinogen of 50 mg/dL decreases the amount of available fibrin in the clotting cascade and can lead to prolonged PTT.

Question 20

A patient has a hematocrit of 65%. Which of the following is true related to coagulation testing?

Accepted Answer

A hematocrit of 65% indicates an increased number of red blood cells and a decrease in plasma volume. This can affect coagulation testing as the ratio of anticoagulant to blood in the collection tube is altered. To compensate for this, the tube must be recollected using a ratio of 0.34 mL of sodium citrate to 4.5 mL of blood. This ensures that the correct ratio of anticoagulant to blood is maintained, and accurate coagulation testing can be performed.

Quiz 45: Laboratory Evaluation of Hemostasis