The Vascular System Part 2

Question 0

Why is EDTA the preferred anticoagulant in platelet system counts?

Answer 0

It prevents clumping of platelets in most patients

Question 1

What anticoagulant is used in automated platelet counts?

Answer 1

EDTA

Question 2

What manual method is used for platelet counts?

Answer 2

Unopette Method

Question 3

What anticoagulant is used in the unopette method?

Answer 3

ammonium oxalate is used as the diluting fluid; it lyses RBCs and platelets are mostly left behind

Question 4

What kind of microscopy is used in the Unopette method?

Answer 4

Phase microscopy retards the wavelength and gives platelets a dark contrast; very hard to see with a light microscope

Question 5

What should you do when you notice that no platelets are seen when performing a differential directly from a fingerstick?

Answer 5

check the edges and tail on low power of the smear for platelet clumps

Question 6

What is the formula for the estimated platelet count?

Answer 6

average number of platelets x 20,000 (make sure you’re in OIF of 200 RBCs)

Question 7

What is the normal range for platelet counts?

Answer 7

150-450 x 10^3/cumm or 150-450 x 10^9 L (in SI units)

Question 8

How will a hemolyzed sample affect an electronic platelet count?

Answer 8

decrease RBCs, decrease HCT, H and H not in balance

Question 9

What should you do if you have a hemolyzed specimen?

Answer 9

Redraw the specimen or a manual Unopette method if ONLY a platelet count is ordered

Question 10

How do Platelet clumps affect an electronic platelet count?

Answer 10

Causes falsely low results

Question 11

How can a valid count be obtained if platelet clumps exist?

Answer 11

Redraw specimen with sodium citrate and multiplly the count by 1.1 for a valid count (because blood:anticoagulant ratio different)

Question 12

How do giant platelets affect an electronic platelet count?

Answer 12

cause falsely low platelet counts

Question 13

How can a valid platelet count be obtained if giant platelets exist?

Answer 13

Performed manual Unopette method for a valid count because they are greater than the threshold for the instrument

Question 14

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

Answer 14

Bleeding time (BT or TBT-Template Bleeding Time)

Question 15

What is the normal reference range for Bleeding Time?

Answer 15

2-10 minutes

Question 16

What six clinical conditions lead to an increased Bleeding Time result?

Answer 16

Thrombocytopenia, aspirin, vWD, Bernard-Soulier Syndrome, Glanzmann’s thrombasthenia, and afibrinogenemia

Question 17

This is the more accurate test than the BT test where platelet adhesion and aggregation following vascular injury are stimulated in vitro.

Answer 17

Platelet Function Analyzer (PFA-100)

Question 18

Describe how the PFA-100 is performed.

Answer 18

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.

Question 19

What is considered the gold standard for platelet function testing?

Answer 19

Platelet Aggregation

Question 20

How is platelet aggregation performed?

Answer 20

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.

Question 21

List six common agonists used in platelet aggregation studies.

Answer 21

ADP (most common), arachidonic acid, collagen, epinephrine, ristocetin, and thrombin

Question 22

This wave of aggregation is reversible and is a direct cause of adding ADP to PRP and causes platelet clumping.

Answer 22

Primary

Question 23

This wave of aggregation is irreversible where alpha and dense bodies release factors.

Answer 23

Secondary

Question 24

What does the ADP aggregation curve look like with aspirin ingestion?

Answer 24

Do not get release factor so only primary curve is present.

Question 25

What does the arachidonic acid curve look like with aspirin ingestion?

Answer 25

absent platelet aggregation, No curve at all

Question 26

What does the ristocetin curve look like in vWD?

Answer 26

Flat line because you need vWF to have aggregation.

Question 27

ONLY _____ aggregation has primary and secondary curves.

Answer 27

ADP

Question 28

This drug inhibits both the release reaction and secondary wave of aggregation.

Answer 28

Aspirin

Question 29

What enzyme is inactivated by aspirin?

Answer 29

cyclo-oxygenase

Question 30

What hormone/final product is blocked with aspirin?

Answer 30

Thromboxane A2 (TXA2)

Question 31

How long does inactivation due to aspirin last?

Answer 31

for entire life of platelet 8-12 days