You might want to give it a few days and drink water to avoid dehydration.
Dehydration can elevate BUN because urea moves freely in and out of cells
and is not osmotically active so with dehydration the transit time is
increased in the renal tubules and more BUN is reabsorbed yielding a high
BUN/creatinine ratio.
Normally the kidneys excrete the urea in proportion to the blood level and
any kidney damage decreases the clearance.
An increase protein load creates more urea and blood is a good source of
protein so GI bleeding increases the BUN/Creat ratio pretty high and is a
tip off to GI bleeding and modest elevations are usually just high protein
diets. This is termed prerenal azotemia.
People can have a normal BUN in the face of renal failure when the muscle
mass or dietary protein is very low. In this case the creatinine is really
what you look at and again muscle mass is important so the creatinine
clearance is more indicative than any single laboratory parameter.
A calculated glomerular filtration rate is usually included with creatinine
levels based on a person with normal mass etc.and any deviations from ideal
mass then a measured creatinine clearance is mandatory.