Platelet Aggregation Results in Increased Transmittance as Measured by a Platelet Aggregometer
Platelet aggregation results in increased light transmittance as measured by a platelet aggregometer. This is the correct answer (option A) based on the principles of optical aggregometry.
Principles of Light Transmission Aggregometry (LTA)
Light transmission aggregometry is the gold standard method for assessing platelet function and works on the following principles:
- Baseline measurement: Initially, platelet-rich plasma (PRP) appears turbid/cloudy, which blocks light transmission
- During aggregation: When platelets aggregate after addition of an agonist, the solution becomes clearer
- Measurement principle: As platelets clump together, more light passes through the sample
- Result interpretation: Increased light transmission (transmittance) indicates platelet aggregation
Technical Details
- LTA measures the change in optical density of a platelet suspension 1
- The platelet aggregometer detects this as increased light transmission through the sample 1
- Standard agonists used include ADP, collagen, arachidonic acid, and ristocetin 1
- Normal platelet aggregation with ADP shows <50% aggregation with 5 μM ADP, while high on-treatment platelet reactivity shows >50-70% aggregation 2
Why Other Options Are Incorrect
- Option B (Decreased transmittance): This is incorrect because aggregation causes platelets to clump together, reducing turbidity and increasing light transmission
- Option C (Increased absorbance): This is incorrect because absorbance decreases during platelet aggregation as fewer particles are available to absorb light
- Option D (Increased light scatter): This is incorrect because while individual platelets scatter light, aggregated platelets form larger complexes that allow more direct light transmission
Clinical Applications of Platelet Aggregometry
Platelet aggregometry is used in various clinical scenarios:
- Diagnosis of inherited platelet function disorders 1
- Monitoring antiplatelet therapy effectiveness 1
- Assessing platelet hyperreactivity as a risk factor for thrombotic events 3
- Quality control of platelet concentrates for transfusion 3
Pre-analytical Considerations
For accurate results, specific conditions must be maintained:
- Blood collection using 0.106 M trisodium citrate as anticoagulant 2
- Discard first 2-5 mL of blood during collection 2
- Allow 15-30 minutes resting time before centrifugation 2
- For platelet-rich plasma, centrifuge at 120-200g for 10-15 minutes 2
- Allow an additional 30 minutes resting time before assay performance 2
Platelet aggregation testing remains a cornerstone of platelet function assessment, with increased light transmittance being the fundamental principle underlying this diagnostic approach.