BUN is an abbreviation for Blood Urea Nitrogen. This is a waste product from the liver and it is processed or removed by the kidneys. In cases of heart failure, kidney failure, or dehydration, this parameter "tends to rise". The texts do not say, how high the value rises before one of these conditions is suspect. Korie's levels have a tendency to be in the lower half of the range, or below 18. BUN can also be elevated by a high protein diet but Korie's diet is low protein which would explain the low values. A low BUN value may indicate pancreas and/or adrenal inactivity.