Urinalysis definately needed to check for crystals, stones & bacterial infections. Also at his age the urine specific gravity should be looked at as a guage for kidney function.
Was there a Thyroid hormone T4 level checked in the blood work? Sometimes that is a separate test.
The howling & fur pulling could be indicating Thyroid issues, which are treatable.
Avoid biting when a simple growl will do
The Spirit Lives As Long As Someone Who Lives Remembers You - Navaho Saying
Vindication ~ For all those pets who became sick or lost their lives from tainted pet food