1B Detecting and Evaluating Coagulation Inhibitors and Factor Deficiencies

3) Which of the following is considered one of the most common coagulation inhibitors? Lupus anticoagulant Anti-factor II Anti-factor V Anti-factor X

Lupus anticoagulant, also known as antiphospholipid antibody, is one of the most common coagulation inhibitors. Anti-factors II, V, and X are less common inhibitors.

14) A mixing study should be performed within what timeframe following the specimen collection? 4 hours 8 hours 24 hours 48 hours

4 hours

13) Which of the following would be acceptable as the "normal" plasma reagent to use in a mixing study? A single patient plasma with a normal PT/aPTT result. A pooled plasma of 2 patient plasmas having normal PT/aPTT results. A pooled plasma from at least 20 healthy donors having normal PT/aPTT results. A pooled plasma of 10 patient plasmas having normal PT/aPTT and 10 patient plasmas having abnormal PT/aPTT results.

A pooled plasma from at least 20 healthy donors having normal PT/aPTT results. An appropriate normal plasma would be prepared by pooling at least 20 plasmas from healthy donors having normal PT/aPTT results. A commercial product is also acceptable.

12) What may cause the following mixing studies results? aPTT Test = 133 sec. 1:1 Mix (Room Temp) = 33 sec. 1:1 Mix (Incubated for 90 min.) = 124 sec. Factor IX deficiency Factor XI deficiency A slow-acting coagulation inhibitor Factor VII deficiency

A slow-acting coagulation inhibitor. In this case, with the pre-incubation aPTT mixing study result "corrected" and the post-incubation aPTT mixing study result "not corrected", a coagulation inhibitor should be suspected. Both anti-factor VIII and lupus anticoagulant have been known to be slow-acting and can exhibit this result pattern. If a factor deficiency were present, there would not be a post-incubation prolongation.

4) Acquired hemophilia A may be the result of which of the following conditions? Anti-factor VIII inhibitor Factor VIII deficiency Warfarin therapy Thrombosis complications

Anti-factor VIII inhibitor. Patients with acquired hemophilia A suffer from a coagulation inhibitor, specifically against factor VIII. Inherited hemophilia A is caused by a deficiency in factor VIII. Neither warfarin therapy nor thrombosis complications can cause acquired hemophilia.

8) Which of the following tests is used to quantify a coagulation inhibitor? Prothrombin time Thrombin time Mixing study Bethesda assay

Bethesda assay The Bethesda assay measures the titer and activity of the antibody present in a patient's sample. Prothrombin time is an initial screening procedure for bleeding disorders and a test used for monitoring anticoagulant therapy. A thrombin time is used to detect heparin interference in an aPTT mixing study. A mixing study is performed to detect the presence of a factor deficiency or coagulation inhibitor but does not quantify the result.

10) Which of these factors may be deficient if both the PT and aPTT are prolonged? Factor II Factor VII Factor VIII Factor XI

Factor II If both the PT and aPTT are prolonged, one or more factors in the common pathway may be deficient. Factor II is in the common pathway along with factors I, V, and X. Factors VIII and XI are intrinsic pathway factors. If either of these factors were deficient, the aPTT would be prolonged, but the PT would be normal. Factor VII is monitored by the PT test. If factor VII were deficient, the PT would be prolonged, but the aPTT would be normal.

9) A patient has a prolonged non-therapeutic PT and a normal aPTT. The physician orders a PT mixing study. The results are as follows: PT Test = 32 sec. 1:1 Mix (Room Temp) = 22 sec. 1:1 Mix (Incubated for 90 min.) = 23 sec. Which factor may be present in abnormally low levels and causing the prolongation? Factor XI Factor VII Factor IX Factor VIII

Factor VII The only factor listed that could cause a prolongation of the PT test if the aPTT test is normal is factor VII. The PT test monitors factor VII along with the common pathway factors. However, the aPTT test is normal. Therefore, no factor in the common pathway would be deficient. Factors VIII, IX, and XI are all factors of the intrinsic pathway and are evaluated with the aPTT test.

2) Which of the following actions would be inappropriate for the investigation of an initially prolonged PT test? Check for clots in the sample Check patient history Check for anticoagulant therapy Immediately cancel the test and request a new sample

Immediately cancel the test and request a new sample The first steps in determining the cause of prolongation should always be to check the sample integrity, check the patient history for liver disease, and ensure the patient is not receiving anticoagulant therapy. Canceling the PT test without investigation of the cause of prolongation is not advised as the patient may have an underlying problem that garners further investigation from the laboratory.

11) What may prevent the detection of lupus anticoagulant in a plasma sample if the blood used for testing is not centrifuged for a sufficient time? Residual red blood cells in the plasma sample Increased platelets in the plasma sample Residual white blood cells in the plasma sample Centrifugation time would not affect the detection of lupus anticoagulant in a plasma sample

Increased platelets in the plasma sample. Increased platelets in the plasma could prevent the detection of lupus anticoagulant (antiphospholipid antibody). Platelet membranes contain a high content of lipids that can cause the antiphospholipid antibody to bind to the platelet membrane, thereby removing it from the plasma so that it is not detected. Blood specimens should be centrifuged for a sufficient time to ensure a residual platelet concentration of less than 10 x 109/L. Residual red or white blood cells do not contain a high content of lipids in their membranes and would not specifically affect the lupus anticoagulant test.

1) What minimum level of a particular factor will cause the aPTT test to become prolonged? Less than 40% Less than 70%

Less than 40% A prolonged aPTT test result will occur only if one or more factor levels that are measured by this test are less than 40% of the normal level.

5) PT = 12 sec. Ref range = 10-13 sec. aPTT = 24 sec. Ref range = 21-34 sec. What would be your next step? Perform a mixing study Report the results Request a redraw of the specimen Repeat the tests

Report the results The results of this PT and aPTT are in normal range. These results can be reported and are not indicative of the need to repeat, order a mixing study, or request a redraw.

7) True or False? Performing a thrombin time to detect heparin contamination in a patient's plasma is done to avoid performing mixing studies for aPTTs that would result in a false positive result.

TRUE. A thrombin time (TT) should be performed to rule out the presence of therapeutic heparin or the presence of a direct thrombin inhibitor.

6) When performing your mixing study, you aliquot your sample plasma and the pooled normal plasma to create your "mix". You then place the mix in a water bath to incubate for 90 minutes before testing your new mixed sample. What is the problem with the steps involved in the procedure above? You don't need to incubate your sample You have forgotten to add a reagent You have not run a PT or aPTT on the new mix before incubating You have incubated too long

You have not run a PT or aPTT on the new mix before incubating In this case, the step missing is the first run of the PT or aPTT test after the mix but before the incubation step. The procedure is not missing a reagent as only the patient plasma and pooled normal plasma are involved in the mixing study procedure. The incubation time is correct, as it is recommended to incubate for 60-120 minutes.