Coagulation Flashcards
(47 cards)
What are the requirements for specimen collection for routine coagulation studies?
Anticoagulant: Light blue top tube with 3.2% buffered sodium citrate.
Purpose: Binds calcium to inhibit coagulation while preserving coagulation factors.
Fill requirement: Must be filled to the proper line to maintain a 9:1 ratio of blood to anticoagulant.
Order of draw: Collected after blood culture tubes and before any other tubes.
Why is the order of draw important when collecting coagulation specimens and CBCs?
Coagulation tests (light blue top) must be drawn before CBC (lavender top EDTA tube).
EDTA in the CBC tube can interfere with coagulation test results if drawn first.
How is a coagulation specimen processed in the lab, and what are PPP and PRP?
Processing: Spun at 3000 rpm for 15 minutes to separate plasma.
PPP (Platelet-Poor Plasma): Used for coagulation testing to avoid interference from platelets (which act as a phospholipid source).
PRP (Platelet-Rich Plasma): Contains higher platelet concentration, not suitable for coagulation tests.
For how long can a PT specimen be left in the lab without spinning? What about PTT? Why?
PT can be left up to 24 hours, and PTT can be left up to 4 hours. This is because the coagulation factors tested in PT are more stable than those in PTT.
How does a short draw affect PT and APTT results?
It falsely prolongs both PT and APTT.
How long is a PT specimen valid after collection, and at what temperatures?
Room temperature (15-25°C): Up to 24 hours
Refrigerated (2-8°C): Up to 24 hours
Frozen (-20°C): Up to 2 weeks
How long is a PTT specimen valid after collection, and at what temperature?
It is stable at room temperature (15-25°C) for up to 4 hours.
Why does PT have longer stability compared to PTT?
The coagulation factors tested in PT are more stable than those tested in PTT.
What is INR, and how is it calculated?
INR (International Normalized Ratio) is the standardized method of reporting PT (Prothrombin Time) to account for variations between labs. It is calculated using the formula:
(Patient PT / Mean Normal PT)^ISI, where ISI (International Sensitivity Index) is provided by the reagent supplier.
What information is needed to calculate INR, and where do you find it?
You need:
Patient PT (from the test result).
Mean Normal PT (determined by the lab).
ISI (provided by the reagent supplier for each lot).
When do you need to re-calculate INR for the analyzer?
Recalculate when:
A new lot of Thromboplastin reagent is used.
The mean normal PT value changes.
Which clinical conditions cause both PT and PTT to be prolonged?
DIC (Disseminated Intravascular Coagulation) and Liver Disease.
Which conditions cause only PT to be prolonged?
Factor VII deficiency or Factor VII inhibitors.
Which conditions cause only PTT to be prolonged?
Hemophilia A/B/C, acquired FVIII inhibitor, VWD (Von Willebrand Disease), and Antiphospholipid syndrome.
Does FXIII deficiency prolong the PTT? Why or why not?
No, because FXIII is not part of the intrinsic pathway measured by the PTT.
Can VWD prolong the PTT? Explain.
Yes, if FVIII is significantly low, since VWF stabilizes FVIII. Low FVIII affects the intrinsic pathway (measured by PTT).
For patients on anticoagulant therapy, what is the risk when results are not within the therapeutic range? What is special about FXII?
The risk is bleeding uncontrollably. FXII is unique because its deficiency does not cause bleeding, as it can be bypassed as a contact factor by direct activation of FXI by thrombin.
What are mixing studies, and how are they interpreted? What follow-up actions are taken based on the results?
Principle: Mixing studies are performed when PT/PTT results are unexpectedly prolonged without a clear history. They differentiate between factor deficiencies and inhibitors.
Interpretation & Follow-Up:
If results remain prolonged after mixing: Suggests an inhibitor → follow up with an inhibitor assay (e.g., DRVVT).
If results normalize after mixing: Suggests a factor deficiency or factor antibody. Incubate for 1-2 hours at 37°C:
If results stay normal: Factor deficiency → perform factor assays.
If results become prolonged: Factor antibody → perform factor antibody assays.
What is the concentration of factor required for normal activity?
50%.
What determines the severity of hemophilia?
The severity of the genetic mutation causing the factor deficiency and the level of activity of the deficient clotting factor.
How are patients on unfractionated heparin therapy monitored, and why?
They are monitored using aPTT and platelet count. aPTT ensures the patient is in the therapeutic range (avoiding overdose/bleeding risks), and platelet count checks for Heparin-Induced Thrombocytopenia (HIT).
How are patients on LMWH therapy monitored, and why is monitoring often unnecessary?
LMWH is typically not monitored due to its safety and predictable dosing. If needed, a FXa assay can be used.
How is a patient on Coumadin monitored? Why?
They are monitored using the PT results because FVII is affected the earliest (it has the shortest half-life) and therefore gives the fastest information on the effectiveness of the drug dosage.
What does aspirin do?
It stops platelets from aggregating at the point of plaque formation and causing arterial thrombosis by irreversibly acetylating a platelet enzyme needed to produce thromboxane A2 (which is a platelet agonist).
