Section 3 Vascular/Plt Testing Flashcards
Purpose of capillary fragility (tourniquet) test
- Evaluates vascular integrity
- Used to test for Dengue viral infection
Capillary fragility test procedure
- Examine arm and back of hand for pre-existing petechiae
- Apply BP cuff
- Apply pressure midway between systolic and diastolic pressures
- Leave cuff on for 5 min
- Remove cuff and wait 5-10 min
- Count petechiae on forearm half inch before cuff and just above wrist, may also use back of hand
Total adult blood volume
4-6 L
Plasma components
Water, proteins, salts, hormones
EDTA tube principle
EDTA chelates calcium needed for blood to clot (anti-coagulant function)
Potential issues with EDTA tube
- EDTA clumpers
- Platelet satellites
- Cold platelet antibodies
Most commonly used tube in hemostasis
Sodium citrate light blue top tube
Sodium citrate tube
- Binds calcium
- Must have full tube 1 part citrate 9 parts blood
Sodium citrate tube CBC report
- Only WBC and plts
- Multiply all values by 1.1 df
PPP vs PRP
PPP = platelet poor plasma
PRP = platelet rich plasma
Both EDTA and sodium citrate tubes show abnormally low platelet counts. What is happening?
Cold platelet antibodies
How do you handle a patient’s blood sample with 55% < Hct < 65%, in relation to anticoag added?
Remove 0.1 ml citrate anticoag from 3 ml tube and don’t perform 1.1 df calc
How do you handle a patient’s blood sample with Hct > 65%?
Use formula to calculate for amount of citrate anticoag to add
Plt < 50 X 10^3 implications
May have issues with surgery
Plt < 10 X 10^3 implications
May have spontaneous bleeding
OHSU critical values
- Plt < 30 X 10^3/mm^3
- Plt > 1000 X 10^3/mm^3
Platelet effectiveness
More dependent on function than numbers
Describe platelet inhibition
Endothelial cells produce PGI2, which reverses platelet activation
Platelet activation can’t be reversed after alpha granule release
How do you measure immature platelet fraction (IPF)?
- Use fluorescent stains and flow cytometry
- More immature, more fluorescence
- Reflects reticulated platelets (containing RNA) in peripheral blood
Meaning of low to normal IPF
- Decreased production
- Aplastic anemia, leukemia, BM suppression, drug effect
Meaning of increased IPF
- Platelet destruction
- ITP, TTP, DIC, drug effect…etc
Platelet function overall steps
- Tissue injury
- Adhesion to collagen
- Shape change
- Platelet aggregation
- Secretion
- Primary hemostatic plug
Purpose of bleeding time test
Evaluates platelet function and numbers only, not dependent on coag cascade
Bleeding time reference range
2-9 min
Describe the analyzer that replaced the bleeding time test
- 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
Closure time (PFA-100) purpose
Screens platelets for ability to adhere and aggregate under in vitro capillary flow conditions
What affects plt activation?
- RBC and plt counts
- Times may be prolonged with Hct < 35% or plt < 150k
What are the normal, plt defect/vWF disease, and aspirin closure times for COL/ADP?
What are the normal, plt defect/vWF disease, and aspirin closure times for COL/EPI?
Describe optical aggregometry (light transmittance)
- 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
Principle of aggregometry
What mediates secondary aggregation in aggregometry?
Release reaction (granules dumped into solution)
Show primary and secondary aggregation
List platelet agonists (aggregating agents)
- ADP
- Epinephrine/norepinephrine
- Collagen
- Thrombin
- Arachidonic acid
- Ristocetin
Which agonists are mostly biphasic?
- ADP
- Epinephrine/norepinephrine
- Thrombin
- Arachidonic acid
- Ristocetin
Single phase with lag phase plt agonist
Collagen
Why is ristocetin associated with primary agglutination instead of aggregation like the other agonists?
Because it uses vWF to stick plts together via GpIb instead of fibrinogen via GpIIb/IIIa
List factors that affect plt aggregation
- pH (8.0 best)
- Temp (37C)
- Stirring constant
- Time at least 30 min
- Cuvette and stir bar size/shape
Which patient lifestyle factors increase plt aggregation?
- Exercise
- Stress
- Obesity
- High fat diet
- Smoking
- Diabetes mellitus
Which patient factors decrease plt aggregation?
- Alcohol
- Aspirin and other anti-inflammatory drugs
Principle of whole blood aggregometry (impedance)
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
Purpose of platelet luminaggregometry
Gives clearer measure of plt secretion so a perfect biphasic curve isn’t necessary
Principle of platelet luminaggregometry
- 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
