Barbara. I'm sure one of the moderators will move this to the introduction section but for your question I found these on-line from a Neph site. Good luck and you have found one great group. We have loads of information and lots of support.
An elevated BUN can be due to many reasons. Some of the common causes are:
1. Dehydration
2. Steroid therapy
3. Blood in the intestines
4. High protein intake in diet
5. Congestive heart failure