If abd. ultrasound & ct are negative and creatinine & bun are consistently normal or slightly below normal, how likely is it to have kidney disease?

Unlikely: The only other issue to be tested is urine for proteinuria, if that this negative you are very unlikely to have kidney disease.

Unlikely: At this moment you do not have kidney disease.

Urine test: I would ensure you have had a urine dipstick done. The first sign of kidney disease is on a urine test. But based on your test as you have mentioned there is not evidence of kidney disease? Why did you have these test done ? What was the trigger symptoms ?