Employee experienced shift change in his hearing. Audio base line was set in 2000. He was tested on 11/5/2012 and a shift was discoverd in left & right ears. Shift was determined to be occupational. He was retested on 11/6/12. Shift in left ear remained. Right ear shift no longer present. Baseline for left ear will be reset. Scheduled to see ENT on 11/21/12.