Hello Sir! BUN(blod urea nitrogen) is a normal product of breakdown of proteins
both in diet as well as body.As the normal kidneys excrete urea efficiently so it rarely exceeds 20 in patients without any kidney disease.The levels can rise when the ability of the kidneys to excrete urea is impaired or when protein breakdown is increased.The levels of BUN vary with age and in children normal levels are 5to 18mg/dL.Creatinine
is also a waste product which is excreted by the kidneys, so levels of creatinine are also carried on along with the BUN. Since in your case creatinine is within normal range and this test is more accurate than the BUN .So nothing much to worry .Have a nice day!