Measurement of apoptotic cells by flow cytometry (tunnel assay)

Apoptotic cells were originally recognized by their characteristic morphology. Since then, a series of biochemical changes have been described. However, it has yet to be established whether any of these changes unequivocally identify an apoptotic cell. In any study of apoptosis, it is important that the presence, or absence, of apoptotic cells is confirmed by morphological examination.