The actress, who plays Dr. April Kepner, described the May 7 episode as "huge", "sad" and "intense".
© ABC
"Everyone bawled their way through the table read for the finale," she told E! Online.
"It's left really unsettled. We don't know what's going to happen to a lot of our characters."
Drew previously hinted that the finale - titled 'Flight' - will be "on par" with the two-part season six finale, 'Sanctuary' / 'Death and All His Friends', which featured a dramatic shooting at Seattle Grace Hospital.
"It will affect everyone, but [this time] it happens outside of the hospital," she explained.
Grey's Anatomy airs on Thursdays at 9/8c on ABC. The eighth season finale airs on May 17 in the US.
