Reflex Testing Flashcards
Mixing Studies:
- principle of the test
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
Mixing Studies:
- testing procedure
- Determine which part of cascade is affected…possible factors
- Rule out heparin contamination
- Mix patient plasma with Pooled Normal Plasma (PNP)
- Proceed with confirmatory testing
Mixing Studies:
- interpretation of results
After ruling out heparin contamination, and mixing with PNP:
- correction: suspect a factor deficiency
- No correction- suspect an inhibitor
How do you determine the presence of Heparin
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
How do you determine if there are Deficient Factors
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)
How do you determine if presence of a circulating anticoagulant
If (50:50) mixture does not correct, suspect an inhibitor (circulating anticoagulant)
- Specific factor inhibitors or
- LLAs (lupus-like anticoagulants)
Factor Assay:
- principle
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
functional Fibrinogen Assay:
- principle
(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)
What are the two classifications of circulating anticoagulants?
- Specific factor inhibitors
2. LLA’s (lupus-like anticoagulants)…aka non-specific inhibitors or antiphospholipid antibodies
Specific Factor Inhibitors:
- definition
antibody that destroys a specific factor in progressive, time-consuming fashion
Specific Factor Inhibitors:
- occurence
- secondary to factor infusions used in Hemophilia A and B treatment (approximately 30%)
- secondary to transfusion
- spontaneously
Specific Factor Inhibitors:
-lab results (screening and mixing studies)
Screening: - Normal PT - Prolonged APTT Mixing studies: - PNP does NOT correct (times will get progressively longer with extended incubation)
Specific Factor Inhibitors:
- confirmatory test(s)
Bethesda titer (to quantify inhibitor)
Lupus-like Anticoagulants:
- definition
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
Lupus-like Anticoagulants:
- occurrence
- 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
Lupus-like Anticoagulants:
- Lab results (screening and Mixing study)
Screening: - Prolonged PT - Prolonged APTT Mixing Studies: - PNP does NOT correct - Times do NOT get progressively longer with extended incubation
Lupus-like Anticoagulants:
- confirmatory tests
- Platelet neutralization test (PNT)
- Dilute Russell’s Viper Venom Test (dRVVT)
Lupus-like Anticoagulants:
- In vitro effects of LLA’s?
- In vivo?
In vitro: Inhibit the assembly of prothrombinase complex (Xa, Va, calcium, and PL)
In vivo: No effect
Method to screen for a suspected deficiency of Fletcher Factor
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
Typical results for deficiency of Fletcher Factor
If abnormal time “partially corrects” think of PK deficiency
- WHY: allows time for “feedback mechanism” to help correct abnormal clotting time
Test that is used to confirm a Factor XIII deficiency
Urea Solubility Test
What are the expected test results for a vascular disorder:
- Platelet Count
- PT
- APTT
- BT
- Platelet Count: N
- PT: N
- APTT: N
- BT: AbN
What are the expected test results for a Fibrinolytic disorder (acquired) :
- Platelet Count
- PT
- APTT
- BT
- Platelet Count: AbN
- PT: AbN
- APTT: AbN
- BT: AbN
What are the expected test results for a quantitative platelet disorder:
- Platelet Count
- PT
- APTT
- BT
- Platelet Count: AbN
- PT: N
- APTT: N
- BT: AbN
What are the expected test results for a qualitative platelet disorder :
- Platelet Count
- PT
- APTT
- BT
- Platelet Count: N
- PT: N
- APTT: N
- BT: AbN
What are the expected test results for a Factor disorder:
- Platelet Count
- PT
- APTT
- BT
- Platelet Count: N
- PT: AbN (dependent on factor def.)
- APTT: AbN (dependent on factor def.)
- BT: N
