Here is what the University of Rochester Medical Center's Health Encyclopedia says about the BUN level:
"On its own, the BUN level does little to tell your provider for sure about your kidney (renal) function. But when it is measured along with creatinine levels, your provider can look at how these 2 levels compare to help find out your kidney function. If this ratio is higher or lower than normal, you may have some type of kidney problem."
So, you could presume your doctor did look at the ratio and everything was fine, or you could call in and ask what the ratio is supposed to be and how yours stacks up, or just call in and ask if any further investigation is warranted.
If it helps, a doctor will almost always do further investigation any time the numbers suggest it.