Reflex Testing

Question 1

Mixing Studies:

- principle of the test

Answer 1

If PT/APTT are normal stop but if either or both are prolonged and can’t be explained by disease, or drugs then mixing studies will be ordered.
- Determines if results are due to either factor deficiency or inhibitor to coagulation

Question 2

Mixing Studies:

- testing procedure

Answer 2

1. Determine which part of cascade is affected…possible factors
2. Rule out heparin contamination
3. Mix patient plasma with Pooled Normal Plasma (PNP)
4. Proceed with confirmatory testing

Question 3

Mixing Studies:

- interpretation of results

Answer 3

After ruling out heparin contamination, and mixing with PNP:

• correction: suspect a factor deficiency
• No correction- suspect an inhibitor

Question 4

How do you determine the presence of Heparin

Answer 4

Add Protamine Sulfate or Hepzyme to the patients plasma and re-run abnormal test:

• if tests are normal - stop the increase was due to heparin
• if tests are still prolonged - proceed

Question 5

How do you determine if there are Deficient Factors

Answer 5

Make a mixture of 50% patient: 50% PNP and run the mixtures.

• If mixture immediately corrects the abnormal results to within 10% of normal suspect a factor deficiency
• If mixture does not correct suspect inhibitor (circulating anticoagulant)

Question 6

How do you determine if presence of a circulating anticoagulant

Answer 6

If (50:50) mixture does not correct, suspect an inhibitor (circulating anticoagulant)

• Specific factor inhibitors or
• LLAs (lupus-like anticoagulants)

Question 7

Factor Assay:

- principle

Answer 7

The degree to which the patient plasma corrects (or fails to correct) a specific factor deficient substrate…is compared to a reference curve/standard curve

Question 8

functional Fibrinogen Assay:

- principle

Answer 8

(modification of the TCT)
- When “excess” thrombin is added to “dilute” patients plasma, the time required for a clot to form is inversely proportional to the fibrinogen concentration (less fibrinogen would be slow to clot / more fibrinogen would be quick to clot)

Question 9

What are the two classifications of circulating anticoagulants?

Answer 9

1. Specific factor inhibitors

2. LLA’s (lupus-like anticoagulants)…aka non-specific inhibitors or antiphospholipid antibodies

Question 10

Specific Factor Inhibitors:

- definition

Answer 10

antibody that destroys a specific factor in progressive, time-consuming fashion

Question 11

Specific Factor Inhibitors:

- occurence

Answer 11

• secondary to factor infusions used in Hemophilia A and B treatment (approximately 30%)
• secondary to transfusion
• spontaneously

Question 12

Specific Factor Inhibitors:

-lab results (screening and mixing studies)

Answer 12

Screening: 
- Normal PT 
- Prolonged APTT 
Mixing studies: 
- PNP does NOT correct (times will get progressively longer with extended incubation)

Question 13

Specific Factor Inhibitors:

- confirmatory test(s)

Answer 13

Bethesda titer (to quantify inhibitor)

Question 14

Lupus-like Anticoagulants:

- definition

Answer 14

Antiphospholipid antibodies, also called LLAs, are blood proteins that appear following a viral infection or during the course of a chronic inflammatory condition like arthritis (e.g. lupus) or cancer

Question 15

Lupus-like Anticoagulants:

- occurrence

Answer 15

• Detectable in 1-2% of people, but usually disappear with 6 weeks
• Those whose LLAs do not disappear present with a 30% risk of thrombosis

Question 16

Lupus-like Anticoagulants:

- Lab results (screening and Mixing study)

Answer 16

Screening: 
- Prolonged PT
- Prolonged APTT 
Mixing Studies: 
- PNP does NOT correct 
- Times do NOT get progressively longer with extended incubation

Question 17

Lupus-like Anticoagulants:

- confirmatory tests

Answer 17

• Platelet neutralization test (PNT)

- Dilute Russell’s Viper Venom Test (dRVVT)

Question 18

Lupus-like Anticoagulants:

• In vitro effects of LLA’s?
• In vivo?

Answer 18

In vitro: Inhibit the assembly of prothrombinase complex (Xa, Va, calcium, and PL)
In vivo: No effect

Question 19

Method to screen for a suspected deficiency of Fletcher Factor

Answer 19

Rerun APTT and extend incubation to 15 minutes (instead go the usual 3-5 minutes) If abnormal time “partially corrects” think of PK deficiency
- WHY: allows time for “feedback mechanism” to help correct abnormal clotting time

Question 20

Typical results for deficiency of Fletcher Factor

Answer 20

If abnormal time “partially corrects” think of PK deficiency
- WHY: allows time for “feedback mechanism” to help correct abnormal clotting time

Question 21

Test that is used to confirm a Factor XIII deficiency

Answer 21

Urea Solubility Test

Question 22

What are the expected test results for a vascular disorder:

• Platelet Count
• PT
• APTT
• BT

Answer 22

• Platelet Count: N
• PT: N
• APTT: N
• BT: AbN

Question 23

What are the expected test results for a Fibrinolytic disorder (acquired) :

• Platelet Count
• PT
• APTT
• BT

Answer 23

• Platelet Count: AbN
• PT: AbN
• APTT: AbN
• BT: AbN

Question 24

What are the expected test results for a quantitative platelet disorder:

• Platelet Count
• PT
• APTT
• BT

Answer 24

• Platelet Count: AbN
• PT: N
• APTT: N
• BT: AbN

Question 25

What are the expected test results for a qualitative platelet disorder : - Platelet Count - PT - APTT - BT

Answer 25

- Platelet Count: N - PT: N - APTT: N - BT: AbN

Question 26

What are the expected test results for a Factor disorder: - Platelet Count - PT - APTT - BT

Answer 26

- Platelet Count: N - PT: AbN (dependent on factor def.) - APTT: AbN (dependent on factor def.) - BT: N