The Vascular System Part 2 Flashcards
Why is EDTA the preferred anticoagulant in platelet system counts?
It prevents clumping of platelets in most patients
What anticoagulant is used in automated platelet counts?
EDTA
What manual method is used for platelet counts?
Unopette Method
What anticoagulant is used in the unopette method?
ammonium oxalate is used as the diluting fluid; it lyses RBCs and platelets are mostly left behind
What kind of microscopy is used in the Unopette method?
Phase microscopy retards the wavelength and gives platelets a dark contrast; very hard to see with a light microscope
What should you do when you notice that no platelets are seen when performing a differential directly from a fingerstick?
check the edges and tail on low power of the smear for platelet clumps
What is the formula for the estimated platelet count?
average number of platelets x 20,000 (make sure you’re in OIF of 200 RBCs)
What is the normal range for platelet counts?
150-450 x 10^3/cumm or 150-450 x 10^9 L (in SI units)
How will a hemolyzed sample affect an electronic platelet count?
decrease RBCs, decrease HCT, H and H not in balance
What should you do if you have a hemolyzed specimen?
Redraw the specimen or a manual Unopette method if ONLY a platelet count is ordered
How do Platelet clumps affect an electronic platelet count?
Causes falsely low results
How can a valid count be obtained if platelet clumps exist?
Redraw specimen with sodium citrate and multiplly the count by 1.1 for a valid count (because blood:anticoagulant ratio different)
How do giant platelets affect an electronic platelet count?
cause falsely low platelet counts
How can a valid platelet count be obtained if giant platelets exist?
Performed manual Unopette method for a valid count because they are greater than the threshold for the instrument
This test is defined as the time it takes for a standardized wound to stop bleeding and is concerned with both the # of platelets and their ability to form a viable platelet plug
Bleeding time (BT or TBT-Template Bleeding Time)
What is the normal reference range for Bleeding Time?
2-10 minutes
What six clinical conditions lead to an increased Bleeding Time result?
Thrombocytopenia, aspirin, vWD, Bernard-Soulier Syndrome, Glanzmann’s thrombasthenia, and afibrinogenemia
This is the more accurate test than the BT test where platelet adhesion and aggregation following vascular injury are stimulated in vitro.
Platelet Function Analyzer (PFA-100)
Describe how the PFA-100 is performed.
Test cartridges are coated with platelet agonists and WB is aspirated through a microscopic cut in the catilage membrane. The time required to occlude the apearature is noted.
What is considered the gold standard for platelet function testing?
Platelet Aggregation
How is platelet aggregation performed?
Platelet agonists/activating agents added to platelet rich plasma causing platelets to clump together, undergo shape change, and release granular contents. Clumping causes a clearing and patterns of light transmittance are charted and analyzed.
List six common agonists used in platelet aggregation studies.
ADP (most common), arachidonic acid, collagen, epinephrine, ristocetin, and thrombin
This wave of aggregation is reversible and is a direct cause of adding ADP to PRP and causes platelet clumping.
Primary
This wave of aggregation is irreversible where alpha and dense bodies release factors.
Secondary
What does the ADP aggregation curve look like with aspirin ingestion?
Do not get release factor so only primary curve is present.
What does the arachidonic acid curve look like with aspirin ingestion?
absent platelet aggregation, No curve at all
What does the ristocetin curve look like in vWD?
Flat line because you need vWF to have aggregation.
ONLY _____ aggregation has primary and secondary curves.
ADP
This drug inhibits both the release reaction and secondary wave of aggregation.
Aspirin
What enzyme is inactivated by aspirin?
cyclo-oxygenase
What hormone/final product is blocked with aspirin?
Thromboxane A2 (TXA2)
How long does inactivation due to aspirin last?
for entire life of platelet 8-12 days
