Section 3 Vascular/Plt Testing

Question 1

Purpose of capillary fragility (tourniquet) test

Answer 1

• Evaluates vascular integrity
• Used to test for Dengue viral infection

Question 2

Capillary fragility test procedure

Answer 2

1. Examine arm and back of hand for pre-existing petechiae
2. Apply BP cuff
3. Apply pressure midway between systolic and diastolic pressures
4. Leave cuff on for 5 min
5. Remove cuff and wait 5-10 min
6. Count petechiae on forearm half inch before cuff and just above wrist, may also use back of hand

Question 3

Total adult blood volume

Answer 3

4-6 L

Question 4

Plasma components

Answer 4

Water, proteins, salts, hormones

Question 5

EDTA tube principle

Answer 5

EDTA chelates calcium needed for blood to clot (anti-coagulant function)

Question 6

Potential issues with EDTA tube

Answer 6

• EDTA clumpers
• Platelet satellites
• Cold platelet antibodies

Question 7

Most commonly used tube in hemostasis

Answer 7

Sodium citrate light blue top tube

Question 8

Sodium citrate tube

Answer 8

• Binds calcium
• Must have full tube 1 part citrate 9 parts blood

Question 9

Sodium citrate tube CBC report

Answer 9

• Only WBC and plts
• Multiply all values by 1.1 df

Question 10

PPP vs PRP

Answer 10

PPP = platelet poor plasma
PRP = platelet rich plasma

Question 11

Both EDTA and sodium citrate tubes show abnormally low platelet counts. What is happening?

Answer 11

Cold platelet antibodies

Question 12

How do you handle a patient’s blood sample with 55% < Hct < 65%, in relation to anticoag added?

Answer 12

Remove 0.1 ml citrate anticoag from 3 ml tube and don’t perform 1.1 df calc

Question 13

How do you handle a patient’s blood sample with Hct > 65%?

Answer 13

Use formula to calculate for amount of citrate anticoag to add

Question 14

Plt < 50 X 10^3 implications

Answer 14

May have issues with surgery

Question 15

Plt < 10 X 10^3 implications

Answer 15

May have spontaneous bleeding

Question 16

OHSU critical values

Answer 16

• Plt < 30 X 10^3/mm^3
• Plt > 1000 X 10^3/mm^3

Question 17

Platelet effectiveness

Answer 17

More dependent on function than numbers

Question 18

Describe platelet inhibition

Answer 18

Endothelial cells produce PGI2, which reverses platelet activation
Platelet activation can’t be reversed after alpha granule release

Question 19

How do you measure immature platelet fraction (IPF)?

Answer 19

• Use fluorescent stains and flow cytometry
• More immature, more fluorescence
• Reflects reticulated platelets (containing RNA) in peripheral blood

Question 20

Meaning of low to normal IPF

Answer 20

• Decreased production
• Aplastic anemia, leukemia, BM suppression, drug effect

Question 21

Meaning of increased IPF

Answer 21

• Platelet destruction
• ITP, TTP, DIC, drug effect…etc

Question 22

Platelet function overall steps

Answer 22

1. Tissue injury
2. Adhesion to collagen
3. Shape change
4. Platelet aggregation
5. Secretion
6. Primary hemostatic plug

Question 23

Purpose of bleeding time test

Answer 23

Evaluates platelet function and numbers only, not dependent on coag cascade

Question 24

Bleeding time reference range

Answer 24

2-9 min

Question 25

Describe the analyzer that replaced the bleeding time test

Answer 25

- Platelet function analyzer (PFA) tests primary hemostasis in artificial vessel simulating the in vivo process of plt adhesion, activation, and aggregation - Tests whole blood - Test cartridges with collagen/ADP or collagen/epinephrine

Question 26

Closure time (PFA-100) purpose

Answer 26

Screens platelets for ability to adhere and aggregate under in vitro capillary flow conditions

Question 27

What affects plt activation?

Answer 27

- RBC and plt counts - Times may be prolonged with Hct < 35% or plt < 150k

Question 28

What are the normal, plt defect/vWF disease, and aspirin closure times for COL/ADP?

Answer 28

Question 29

What are the normal, plt defect/vWF disease, and aspirin closure times for COL/EPI?

Answer 29

Question 30

Describe optical aggregometry (light transmittance)

Answer 30

- It's a reference method where aggregating agent is added to PRP (PPP is used as blank) - Plasma becomes clearer (**decreased** turbidity) as platelets aggregate, so light transmitted **increases**

Question 31

Principle of aggregometry

Answer 31

Question 32

What mediates secondary aggregation in aggregometry?

Answer 32

Release reaction (granules dumped into solution)

Question 33

Show primary and secondary aggregation

Answer 33

Question 34

List platelet agonists (aggregating agents)

Answer 34

- ADP - Epinephrine/norepinephrine - Collagen - Thrombin - Arachidonic acid - Ristocetin

Question 35

Which agonists are mostly biphasic?

Answer 35

- ADP - Epinephrine/norepinephrine - Thrombin - Arachidonic acid - Ristocetin

Question 36

Single phase with lag phase plt agonist

Answer 36

Collagen

Question 37

Why is ristocetin associated with primary agglutination instead of aggregation like the other agonists?

Answer 37

Because it uses vWF to stick plts together via GpIb instead of fibrinogen via GpIIb/IIIa

Question 38

List factors that affect plt aggregation

Answer 38

- pH (8.0 best) - Temp (37C) - Stirring constant - Time at least 30 min - Cuvette and stir bar size/shape

Question 39

Which patient lifestyle factors **increase** plt aggregation?

Answer 39

- Exercise - Stress - Obesity - High fat diet - Smoking - Diabetes mellitus

Question 40

Which patient factors **decrease** plt aggregation?

Answer 40

- Alcohol - Aspirin and other anti-inflammatory drugs

Question 41

Principle of whole blood aggregometry (impedance)

Answer 41

Add aggregating agent to whole blood and plts adhere to electrode and one another, which **impedes the DC current**, thus increase in impedance is directly proportional to platelet aggregation

Question 42

Purpose of platelet luminaggregometry

Answer 42

Gives clearer measure of plt secretion so a perfect biphasic curve isn't necessary

Question 43

Principle of platelet luminaggregometry

Answer 43

- Thrombin used to induce plt secretion - As ATP is released with secretion, it oxidizes luciferin-luciferase to generate cold chemiluminescence directly proportional to ATP conc