When I didn't hear from my step mom since yesterday afternoon and through the night, I figured no news was good news, and I had a certain calm about me as I fell asleep. Sure enough, this morning when I went to visit my dad in the hospital, good news awaited me. My step mom was there -- her son had come to take over during the night so she could go home to sleep -- and we were able to talk at length since my dad was fast asleep. His kidney function was back to normal! The urologist had indeed discovered there was a blockage due to an enlarged prostate (a normal thing that happens in many older men), and that he could perform minor laser surgery to correct it. The catheter had by-passed the blockage, making is possible for his urine to be fully expelled, and therefore allowing his kidneys to return to normal.
His surgery was scheduled for Monday morning. In the meantime he will remain in the hospital, I assume because they don't want to take the risk that his catheter might get pulled out, since without the catheter, his kidneys would begin to fail again.