My kidney function test show low levels of urea, 13.00 mg/dl.

Not a problem: The reference range for urea is the level for most folks who are not obviously sick. Low serum urea is never a problem. If you're obviously sick with something else, it may provide a clue -- but probably not. I hope you're not restricting dietary protein for some reason. "treat the person, not the numbers" -- but i'm glad you're asking and remaining proactive.