Platelet Aggregation Measurement

Specimen

citrated platelet-rich plasma is continuously stirred in a platelet aggregometer with a light beam passed through the suspension
platelet aggregation in response to added chemical stimulus is then monitored by changes in light transmittance.
a discoid to spheroidal shape change is seen as an initial decrease in transmittance & the subsequent platelet clumping allows more light to pass thus is recorded as an increase in light transmittance
some instruments are equipped with a 2nd channel to measure release of ATP from platelet dense granules
this is accomplished by addition of firefly luminescence substrate & enzyme (luciferin & luciferase) to the platelet-rich plasma
released ATP functions as a cofactor for light emission by luciferase
the emitted light is recorded by a 2nd photodetector
reagents used to stimulate platelet aggregation include:

Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 705