Hemostasis Lab Testing Flashcards
What test measures the time required for anticoagulated whole blood to occlude a standard aperature (closure time)?
PFA-100
The aperture in PFA-100 is covered by 2 types of thin membranes, what are they and what are they used for?
Collagen and Epinephrine (Col/Epi)
-Sensitive to global platelet defects
Collagen and ADP (Col/ADP)
-Sensitive to Drug induced platelet defects (Aspirin)
Besides platelet dysfunction, what might cause a prolonged Closure Time (PFA-100)?
- Anemia (Hct <25%)
- Thrombocytopenia (<100)
What specimen type is used for Platelet Aggregometry and how is it prepared?
Platelet rich plasma
-slow centrifugation of whole blood
What Agonists are used in Platelet Aggregometry? (5)
- ADP
- Epinephrine
- Arachidonate
- Collagen
- Ristocetin
Platelet Aggregometry - Curve:
- Biphasic
- What causes the secondary wave?
- ADP (Low Dose)
- Epinephrine
-Platelet degranulation
Platelet Aggregometry - Curve:
-Monophasic (primary aggregation only)
- ADP (High Dose)
- Collagen
- Ristocetin
What is the most common cause of an Abnormal Agrregometry? What Agonists is used?
Medication
-Decreased aggregation with Arachidonate
Abnormal Aggregometry in Glanzmann Thrombasthenia.
-Poor response to ALL agents EXCEPT Ristocetin
What causes an Absent Secondary phase with Epinephrine and ADP (Low)?
- Storage pool defects
- Aspirin
What Abnormality can you see in myeloproliferative neoplasms?
-Poor response to Epinephrine
What Abnormal Aggregometry pattern is the Hallmark dor von WIlledbrand Disease? what other syndrome has this pattern?
Response to everything EXCEPT Ristocetin
-Bernard-Soulier syndrome
Activated Clotting Time (ACT):
- Use
- Setting
- Specimen type
- Point of care test to monitor high dose Heparin therapy
- Cardiopulmonary bypass surgery
- Whole blood
Activated Partial Thromboplastin Time (aPTT):
-What is added to citrated plasma
- Phospholipid
- Contact activator of F12 (silica, kaolin, etc)
- Excess calcium
*Time to clot is formation is the aPTT
Prolongation of the aPTT is caused by?
- Factor deficiency
- Inhibitor
Which pathways/factors are tested in aPTT?
Intrinsic Pathway
-12,11,9,8
Common Pathway
-5,10,2,1
Prolongation of both PT and aPTT is caused by what factor deficiencies?
Common Pathway
-1,2,5,10
A factor generally must be what percentage to cause prolonged aPTT?
30%
Elevation of what factor may shorten the aPTT?
F8 (VIII)
What factor is involved with an INcreased PT and a Normal aPTT? (clinical considerations;4)
Factor 7 (FVII)
- Liver disease
- Vit. K deficiency
- Warfarin
- Inherited factor deficiency
If mixing study fails to correct the aPTT, what should be suspected?
-Inhibitor
If mixing study corrects the aPTT, what should be suspected?
-Factor deficiency
What inhibitor shows immediate correction but prolongation of the incubated aPTT over time?
Anti-Factor8 (VIII) antibody.
aPTT is used to monitor what?
Heparin therapy (unfractionated heparin)
In circumstances where the aPTT is unreliable, what assay should be used to monitor Heparin therapy?
Factor Xa assay
The anticoagulant (3.2% trisodium citrate) in collection tubes, ~0.5 mL, is intended to result in a whole blood to anticoagulant of ___, and a ratio of plasma to anticoagulant of ___, assuming a normal hematocrit (35-55%).
- 9:1 (whole blood:anticoagulant)
- 5:1 (plasma: anticoagulant)
How does a high hematocrit (>55%) affect the aPTT?
- Less plasma
- sample over coagulated
- Clotting time prolonged
What assay can be used to monitor either unfractionated or low molecular weight heparin?
Anti-Xa assay (Heparin antifactor Xa assay)
How is the Anti-Xa assay set up?
Patient plasma is added to known amount of factor Xa with excess antithrombin
What is the MOA of the Anti-Xa assay?
- Heparin from patient plasma stimulates antithrombin to inhibit factor Xa
- Quantity of the residual factor Xa is measured with a chromogenic substrate
- Residual Xa is subtracted from the initial Xa to determine the anticoagulant concentration
T/F: The anti-Xa assay is not affected by underfilled collection tubes and is unaffected by abnormal factor levels.
True
What assay is performed to determine the titer of anti-fVIII antibody?
Bethesda assay (factor VIII inhibitor assay, anti-fVIII antibody assay)
What factor generates D-dimer?
-Mechanism>
Factor XIII
-Covalently linking the D regions of fibrin molecules
What dissolves fibrin clots?
Plasmin
*Incapable of breaking up D-dimers
What does the presence of D-dimers indicate?
Fibrin has been formed and then degraded
When are D-dimers and fibrin degradation products (FDPs) increased? (5)
- Thrombosis
- Significant bleeding
- A. fib
- CHF
- Cirrhosis
What factor assays are PTT based? (4)
8, 9, 11, 12
- FVIII
- FIX
- FXI
- FXII
What factor assays are PT based? (3)
2, 7, 10
- FII
- FVII
- FX
What factor assay can be either PT or PTT based?
5 (FV)
Choice of factor assay depends upon screening test findings:
-Prolonged aPTT, Normal PT (4)
8, 9, 11, 12
- FVIII
- FIX
- FXI
- FXII
Choice of factor assay depends upon screening test findings:
-Normal aPTT, Prolonged PT (1)
*what should also be considered?
7 (FVII)
*1,2,5,10 (common pathway), because PTT is insensitive to mild to moderate common factor deficiencies. Thus can sometimes produce a prolonged PT with normal PTT
Choice of factor assay depends upon screening test findings:
-Prolonged aPTT, Prolonged PT
1,2,5,10 (common pathway)
T/F: The lower the fibrinogen, the longer the clotting time.
True
How is the Prothrombin Time (PT) set up?
A source of Tissue Factor and phospholipid (thromboplastin) is added to Citrated plasma with excess Calcium
-The time to clot formation is the PT
What causes prolongation of the PT?
- Factor 7 deficiencies
- Factors 2,5,10 or Fibrinogen (common factor deficiencies)
- Inhibitors
PT or aPTT, which is more sensitive to common pathway deficiencies (F2,5,10)?
PT
The PT forms the basis of INR, which is used to monitor what?
Warfarin (coumadin) therapy
What is the Chromogenic Factor X assay useful for?
*different than Anti-Xa assays)
Monitoring warfarin in the presence of:
- Lupus anticoagulant
- Hirudin
- Argatroban
For the Thrombin Time (TT), thrombin is added to patient plasma and the time to clot formation is the TT. What causes a prolongation of the TT?
- Fibrinogen deficiencies
- Defective fibrinogen (dysfibrinogenemia)
- Inhibitors (Heparin, Hirudin, Argatroban, or FDPs)
If the TT is prolonged, the presence of Heparin can be confirmed by what? (2)
- Reptilase time is normal in presence of Heparin
- 1:1 mix will fail to correct in presence of Heparin
