Apoptotic cells undergo an ordered series of molecular and morphologic changes, including caspase activation, chromatin condensation and destruction, destruction of the nuclear envelope, and membrane "blebbing." The classic and still gold-standard test is electron microscopy (see figure at right), says John Reed, an apoptosis researcher and president and CEO of the Burnham Institute for Medical Research in La Jolla, Calif. But as most labs don't have EM technicians on staff, researchers often use surrogate assays instead.
In the illustration in this Flash diagram, we highlight six common approaches to measuring apoptosis. But, stresses Reed, "You need to be cautious of how you interpret." Other than caspase activation, none of these tests indicates apoptosis so much as cell death in general. Reed's recommendations: run multiple assays, and watch your kinetics.