6-CFDA has been used to differentiate viable cells from apoptotic cells. Live cells that are not apoptotic accumulate 6-carboxyfluorescein but do not accumulate annexin. CFDA enters cells and is hydrolyzed more slowly than FDA. CFDA and FDA hydrolysis obey Michaelis-Menten kinetics with Km values of around 19 and 2 µM, respectively.