There are a number of ways in which blood tests could be abnormal after a kidney transplant. The risks would depend on some of those answers and it's impossible to give an intelligent opinion without more specifics.
In general, It doesn't hurt to get your local physician in communication with someone experienced in diving medicine.
DAN can assist in such referrals.
I'd be happy to tell you what I know about diving medicine and a particular problem, but with health problems and individuals, the devil is truly in the details, and a careful consultation is probably the best way for you to get accurate advice tailored to your individual health problem.
I don't know of any reason medically that would automatically disqualify a kidney transplant recipient from diving, but there are a lot of factors to consider based on medications, the cause of the original kidney disease, and your health in other respects.
I know this is a very nonspecific answer, but it's the best advice I can give.
Hoping to see you either diving or snorkeling,
John Reinertson