Lecture 16 Hemostasis Testing Flashcards
For proper collection concerns, what happens if the tourniquet is on for greater than 1 minute?
Hemoconcentration and increased fibrinolytic activity.
How can repeated probing looking for a vein affect coagulation test results?
Tissue fluid from repeated probing will decrease coagulation results as TF3 is responsible for activating extrinsic and intrinsic pathways.
Why is it needed to draw a discard tube in “request lines”?
Lines to administer medication and that can be used to draw blood often contain heparin to prevent clotting and will elevate coagulation results. Therefore a discard tube is needed to be drawn to remove heparin + blood in the lines prior to collection of blood.
What is important in the order of draw for coagulation testing?
No chance of Heparin contamination.
Why are hemolyzed samples not acceptable for coagulation testing?
Hemolysis leads to increase of phospholipids which then accelerates coagulation process leading to decreased coagulation times.
Why are icteric or lipemic samples not acceptable for coagulation testing?
Icteric or lipemic samples can alter times in instruments using photometric methods.
Why are 3.2% Sodium Citrate tubes preferred for coagulation studies?
- Chelates calcium so sample will not clot and consume clotting factors.
- Best preserves labile factors V and VIII.
- Best for platelet function tests.
- Most sensitive to the effects of heparin anticoagulation therapy.
Why is 3.8% Sodium Citrate tubes not recommended for coagulation studies?
Chelates too much of the calcium.
Why is it important to fully fill the sodium citrate tube for coagulation studies?
If not in proper ratio of blood to anticoagulant, excess anticoagulant will react with reagent calcium and produces elevated results.
What effect will having a Hct > 0.55 such as in polycythemia do to coagulation test results?
Falsely increase times.
What is done to correct of a high Hct > 0.55 for coagulation testing?
Need to adjust anticoagulant.
1. Remove anticoagulant, used formula to calculate proper volume of Na Citrate.
2. (0.00185)(vol. of whole blood)(100%-Hct) = req’d anticoagulant in mL.
3. Remove excess anticoagulant (0.5 mL - required) and recollect blood in the modified tube.
Why is it important to ensure that specimens for coagulation testing remained capped?
Uncapping samples adversely affects factors by increasing pH and falsely increasing PT and APTT times.
At what temperature should samples be stored at and why?
Samples should be stored at room temp (18-24C) as refrigeration will activate Factor VII, destroy platelet activity by activation and cause precipitation of large vWF multimers.
What would happen if the coagulation blood sample was stored above 24C?
Heat causes deterioration of labile factors V and VIII, falsely increasing results.
What is the time frame from collection to testing for PT/INR testing?
24 hours
What is the time frame from collection to testing for APTT testing and why? and what can they not contain?
Can be uncentrifuged or centrifuged samples, but must be tested within 4 hours from time of collection to reduce deterioration of labile factors V and VIII.
Cannot contain unfractioned heparin (UFH)
If APTT samples contain UFH, how should they be processed?
Samples containing UFH must be centrifuged within 1 hr from time of collection and tested within 4 hrs. Plasma may remain on packed cells.
Why do samples containing UFH need to centrifuged within 1 hr from collection?
Centrifugation within 1 hr is performed to reduce the effect of heparin neutralization by platelet granule Platelet Factor 4 (PF4) by stopping platelet contact with RBCs.
Why is it critical to centrifuge samples? What should the plasma platelet count be?
Samples should be spun at a speed and for a time to remove RBCs and platelets (this removes excess phospholipids that can affect coagulation results;
Plasma platelet count should be <10x10^9/L.
What is done if sample cannot be processed within the required time frame?
- Sample must be centrifuged within 1 hr of collection.
- Transfer sample avoiding buffy coat (platelets) with plastic pipette into plastic tube. Do not use glass as this will activate the intrinsic system.
- Sample is sealed, frozen and can be stored for 2 weeks at -20C or longer periods at -70C.
- Thaw frozen sample rapidly before testing at 37C to prevent deterioration of factors, mixed and tested within 1 hr.
What are methods for validating laboratory coagulation results?
- Instrument calibration.
- Quality control (internal and external)
- Recognition of erroneous results and follow-up.
- Delta checks
- Proper electronic/paper recording of results.
What are some preanalytical considerations to be aware of to avoid erroneous lab results (e.g. interferences)?
- Tube properly filled.
- Signs of interference (hemolysis, lipemic, icteric, etc.)
- Check for clot in sample. Small clots may shorten times due to partial activation of factors while a fully clotted sample causes markedly elevated results.
- Phone for patient background (Liver disease, medication, heparin therapy, lupus inhibitor, antibiotics, etc.).
What follow-up can be done to avoid erroneous results?
Further testing (1:1 mixing studies, etc.)
What are some post analytical consideration after testing?
- Recognition of stat and critical results and proper phoning.
- Proper validation and release of records to wards.
- Proper storage of all samples and tested materials.
Why do we perform coagulation testing?
- To detect factor deficiencies in extrinsic and intrinsic pathways of coagulation.
- Monitor anticoagulant therapy for people with thrombotic conditions.
- Detect platelet qualitative defects.
What drug that is used as an anticoagulant therapy is also an active ingredient in rat poisin?
Warfarin
What are some brand names for Warfarin?
Coumadin and Jantoven.
Warfarin is the generic name.
Where does warfarin originate from?
Warfarin is part of a group of plant-based compounds called coumarins.
Why is heparin used for in patients?
To treat thrombotic conditions.
Why is the Prothrombin Time Test a one step test?
The PT reagent contains everything required to initiate and complete clotting in the extrinsic and common pathway.
What does the PT test measure?
Directly in measures the time for coagulation which is indicative of factors VII, X, II and I.
What is in the PT reagent?
Thromboplastin –> Lyophilized rabbit brain which provides Tissue Factor, phospholipids, and calcium.
What does INR stand for?
International normalization ratio.
Derived from the PT result.
Why is the INR calculated?
- Various PT reagents differ in sensitivity to changes in Vitamin K clotting factors even though plasma Warfarin concentration are the same. This made interpretation of patient’s anticoagulant status difficult.
- Different PT results occur with different reagent lot numbers methods, instrumentation and vary from lab to lab.
- INR was developed as a way to standardize results which would be consistent from lab to lab.
What is the formula for INR?
INR = (Patient PT / Mean PT for lab)^ISI
ISI value is from WHO testing for that manufacturer.
What is the reference range for INR?
0.9 to 1.1
What does ISI stand for?
International Sensitivity Index (ISI)
How is the ISI value derived?
ISI is measured by WHO in comparison to their reference reagent thromboplastin. When companies manufacture a new lot of PT reagent they send a sample of their reagent to WHO to determine this value.
ISI (WHO) = 1.0 (gold standard).
What does it mean if the ISI is greater than 1.0?
Reagents > 1.0 for ISI are less sensitive to factors depleted by Coumadin.
What is the implication of using the INR?
Therapy can be monitored regardless of where analysis is being done providing consistent INR results from region to region and lab to lab.
What is the ideal ISI value?
PT reagent should ideally be close to ISI of 1.0 to be sensitive to detect small levels of factor depletion due to oral anticoagulant activity.
Can INR values be trusted early in Warfarin treatment? When can you trust them?
No, early in Warfarin treatment affected factors have different half lives.
After 3 days factor levels have stabilized, clinical management will be easier to achieve.
Are INR values affected by heparin?
No INR is not usually impacted by the presence of heparin, unless levels are really high.
Some reagents have a heparin neutralizer in them.
