platelet swirling platelet swirling platelet swirling is a noninvasive method for testing the quality of platelet-rich plasma (prp). platelet swirling is caused by light diffraction due to the alignment of normal disc-shaped platelets. these discs align light that is diffracted, creating a cloud- or swirl-like appearance. platelet swirlingpurposetesting the quality of platelet-rich plasma results of a platelet swirling test are recorded as positive or extensive swirl, moderate or intermediate swirl, and absent or negative swirl.