cea levels and kidney failiure after treatment???

My dad was diagnosed with stage II rectal last nov. He had chemo/rad for 1 month, then surgery, then 5 months of chemo ending in August. He then was unable to get a good night of sleep due to urinating every hour. The dr. determined enlarged prostate. A couple weeks later he ended up in the hospital with kidney failure and congestive heart failure all due to the enlarged prostate. He was catheterized for 3 weeks. This past Wednesday he had his cea levels checked. The dr. called and wanted him to have a pet b/c his cea is elevated. They say it could be cancer again or b/c of the kidney failure (kidney dr. says his kidneys are not back to normal yet). We are definately freaking out b/c when he was in the hospital they did a ct, ultrasound, and chest x-ray which showed nothing.
Does anyone have any experience or comments on this? We go to the dr. on monday to find out. It is so unbelievable to think the cancer is already back (when no lymph nodes were involved). Is the cea level very accurate? Please Help!