I had a partial nephrectomy in 2008. My lab results were normal for bun and creatinine however bun/creatinine ratio was high (25). Should I be concern?

No. Many times the ratio is high but relative to the individual values a low normal creatinine and a high normal BUN will show an abnormal ration but would be normal individual numbers. The benefit ais thta it makes one look at the numbers more carefully but is not used for a diagnosis.