Question 1

A thrombin time test was performed and the resulting clotting time exceeded the reference range. A 1:1 mixing study with normal pooled plasma was done that corrected the result to the normal range. Which abnormality is suspected?

Accepted Answer

The correction of the clotting time to the normal range after a 1:1 mixing study with normal pooled plasma suggests a deficiency in a clotting factor, in this case, fibrinogen deficiency. This is because the addition of normal plasma provides the deficient factor (fibrinogen), thereby correcting the clotting time.

Question 2

Which is the anticoagulant of choice for samples to be tested in the PT test?

Accepted Answer

Sodium citrate, 3.2%, is the anticoagulant of choice for samples to be tested in the PT test as it preserves clotting factors and inhibits the coagulation cascade by binding to calcium ions. This ensures that the patient's actual clotting time can be accurately determined in the laboratory.

Question 3

If fibrin is discovered in a citrated plasma sample, the following test(s) will not be affected and can still be run:

Accepted Answer

Fibrin presence indicates clotting, which affects all coagulation tests like PT, APTT, and Thrombin time, making them unreliable.

Question 4

In the fibrinogen activity assay, a prolonged clotting time obtained when testing patient plasma indicates:

Accepted Answer

Prolonged clotting time in the fibrinogen activity assay indicates a decreased amount of fibrinogen in the patient's plasma, usually below 50 mg/dL. This could be due to various conditions such as liver disease, DIC, or genetic deficiencies. Increased fibrinogen levels would result in a shorter clotting time. Pregnancy does not directly affect the fibrinogen levels, although they do increase slightly during pregnancy.

Question 5

The reptilase test will be abnormally prolonged:

Accepted Answer

The reptilase test is specifically designed to measure fibrinogen levels in the blood, independent of heparin presence, vitamin K effects, or recent thrombosis. It will be prolonged in conditions of hypofibrinogenemia, where there is a deficiency of fibrinogen, a crucial clotting factor.

Question 6

The __________ is the assay used for the one-stage quantitative method for factors VIII, IX, XI, and XII?

Accepted Answer

The one-stage quantitative method for factors VIII, IX, XI, and XII is measured using the activated partial thromboplastin time (APTT) assay. This assay measures the time it takes for a clot to form when calcium and an activating agent are added to the patient's plasma. The APTT is a key test in the evaluation of coagulation disorders and is used to monitor the effectiveness of anticoagulant therapy.

Question 7

Which anticoagulant is used for samples to be tested in the reptilase test?

Accepted Answer

Sodium citrate, 3.2% is the best anticoagulant choice for reptilase test samples as it prevents clotting by binding to calcium ions, which are required for clotting reactions. Other anticoagulants can interfere with the test and lead to false results.

Question 8

What is the dilution buffer used in the determination of fibrinogen activity?

Accepted Answer

Owren's Veronal buffer is the dilution buffer commonly used in the determination of fibrinogen activity. Electrolyte buffer and Tris buffer may also be used, but Owren's Veronal buffer is the preferred choice as it provides the most accurate results.

Question 9

Fibrinogen can be quantitatively measured by a modification of the __________ because the latter clotting time of dilute plasma is inversely proportional to the concentration of fibrinogen.

Accepted Answer

The thrombin time (TT) is used to measure fibrinogen levels because the clotting time of dilute plasma is inversely proportional to the concentration of fibrinogen.

Question 10

In the one-stage quantitative assay for factors II, V, VII, and X the __________ is the test system used, with specific-factor-deficient plasmas added to normalize all other factors but the one being measured.

Accepted Answer

The one-stage quantitative assay, also known as the prothrombin time (PT) test, uses a test system with factor-deficient plasmas to normalize all other factors except the one being measured (in this case, factors II, V, VII, and X).

Question 11

To diagnose a cause, which steps should be taken if, when performing a thrombin time, the patient's average clotting time significantly exceeds the reference range?

Accepted Answer

Running the test using a 1:1 mixture of patient's plasma and normal plasma helps to determine if the clotting factor deficiency is due to a factor in the patient's plasma or if it is due to a inhibitor in the patient's plasma that is blocking clotting factors. If there is no improvement in the clotting time with the 1:1 mixture, then it is likely that the patient has a clotting factor deficiency. Running the test using a 1:5 mixture of patient's plasma and normal plasma may dilute the clotting factors too much and could potentially cause an incorrect result. Resulting the first clotting time would not provide additional information.

Question 12

The Clauss fibrinogen assay involves clotting dilutions of both patient's test plasma and calibration plasma with an excess of __________.

Accepted Answer

The Clauss fibrinogen assay involves adding an excess of thrombin to both patient's test plasma and calibration plasma to initiate clotting. The time taken for the clot to form is then measured and compared to that of the calibration plasma to determine the fibrinogen concentration of the patient's plasma.

Question 13

The __________ is the time required for thrombin to convert fibrinogen to an insoluble fibrin clot.

Accepted Answer

TT (thrombin time) measures the time it takes for thrombin to convert fibrinogen to an insoluble fibrin clot.

Question 14

The PT test is sensitive to the vitamin __________ factors and therefore useful as a means of monitoring oral anticoagulant therapy.

Accepted Answer

The PT test is dependent on vitamin K factors, specifically factors II, VII, IX, and X. Therefore, monitoring the results of the test can help determine the effectiveness of oral anticoagulant therapy, which works by inhibiting the activity of these vitamin K-dependent factors.

Question 15

In most one-stage quantitative assay method for factors VIII, IX, XI, and XII, a 1:10 dilution is considered __________ percent factor activity.

Accepted Answer

A 1:10 dilution is considered 100 percent factor activity. This means that the concentration of the factor in the diluted sample is expected to be 10 times lower than in the undiluted sample, but since the activity is proportional, the percentage of activity is the same. For example, if the undiluted sample has 100% factor activity, the diluted sample is expected to have 10% factor activity, but this still represents 100% of the factor's activity in the sample.

Question 16

In patients with __________, the PT is prolonged as a result of a change in the ratio of anticoagulant to plasma.

Accepted Answer

In polycythemia, the increased red blood cell mass can lead to a relative decrease in plasma volume, affecting the ratio of anticoagulant to plasma and prolonging the prothrombin time (PT).

Question 17

Reptilase hydrolyzes the fibrinopeptide __________ from the intact fibrinogen molecule in contrast to thrombin, which hydrolyzes fibrinopeptide __________ from fibrinogen.

Accepted Answer

Reptilase hydrolyzes the fibrinopeptide A from the intact fibrinogen molecule, while thrombin hydrolyzes fibrinopeptide A/B from fibrinogen.

Question 18

Stabilization of the fibrin clot depends on plasma factor __________, which converts hydrogen bonds to covalent bonds by transamination.

Accepted Answer

Stabilization of the fibrin clot depends on factor XIII, also known as fibrin-stabilizing factor, which cross-links fibrin monomers through the formation of covalent bonds by transamidation. Factors X, XI, and XII are involved in the clotting cascade, but not in the stabilization of the fibrin clot.

Question 19

The normal adult value for fibrinogen is approximately __________.

Accepted Answer

The normal adult value for fibrinogen is approximately 200-400 mg/dL. Fibrinogen is a blood plasma protein that's converted into fibrin in the blood clotting process.

Question 20

In performing a one-stage quantitative assay method for factor II, results are obtained from an activity curve made from dilutions of normal reference plasma and factor __________ plasma.

Accepted Answer

In a one-stage quantitative assay method for factor II, factor II-deficient plasma is used to create an activity curve by comparing it to dilutions of normal reference plasma. This allows for the determination of the activity of factor II in a sample by seeing how it compares to a known factor II deficiency.

Quiz 33: Coagulation Procedures