Hi Mary, I would start by calling the Mayo Clinic where he is a patient. You'll find all the numbers here: http://mayocl.in/1mtmR63
Ask if he as a current Mayo Clinic patient with nephrology, does he need to submit a new appointment request by phone or through the patient portal. I would also ask if it is better in his case to have his doctor submit the referral for pulmonology or to self refer.