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
