I agree w/ Ellie May, 38 is not that high and could be just dehydration, I pray it's just that.
My last Yorkie was 10yr when an ultrasound revealed she had one kidney that was not normal in size. I freaked out!!! She was put on k/d that day and her BUN was never below 40ish her creatine (SP) was also elevated. I want to say that creatine points more towards KIDNEY FUNCTION..
She lived to almost 15yr, the last 2 mo of her life (when i found this site

) her BUN was over 100 sometimes over 160ish. She was given SQ fluids daily, but that didn't even make a difference at the end.
I learned about Azodyl (after I joined YT) and researched the heck out it, i finally ordered it and recieved it the day before we put her to rest. I wish i just ordered it from day one, who knows maybe it could of made a difference. From what I've read and researched people have had good results.
If in fact it turns out that his kidneys are "bad" please get your baby on it, your baby is so young that it may make a difference.
My doctor never heard of it until i printed it out and brought it in to him...Some Dr. just aren't aware.
THANK GOD FOR YT!!!!
Please keep us updated!!