A 65-year-old man is evaluated during a follow-up visit for a preemptive living donor kidney transplant 6 months ago, with a postoperative course complicated by an episode of acute cellular rejection requiring antithymocyte antibody induction. He has done well since then. He has a 10-year history of chronic kidney disease due to diabetic nephropathy and a 35-year history of type 1 diabetes mellitus. Basal cell carcinoma was removed from his nose 2 years ago. Current medications are tacrolimus, mycophenolate mofetil, valganciclovir, and prednisone, 5 mg/d.

On physical examination, temperature is 37.0 °C (98.6 °F), blood pressure is 135/78 mm Hg, pulse rate is 80/min, and respiration rate is 14/min. BMI is 22. There is no lymphadenopathy. Actinic keratoses are present on the forehead. The lungs are clear. The abdomen is nontender without organomegaly. The kidney allograft in the left pelvis is nontender with a well-healed scar. There is no peripheral edema.

Laboratory studies show a serum creatinine level of 1.2 mg/dL (106.1 µmol/L).

In addition to age- and sex-appropriate screening, which of the following should this patient be evaluated for?