Participants were recruited from nephrology and infectious disease clinics at Mt Sinai Hospital and St Vincent’s Medical Center in New York, Tufts Medical Center in Boston and University of Alabama at Birmingham, as well as from HIV community centers in Boston, Massachusetts. Eligible patients included those who were older than 18 years of age, on stable ART for at least three months, with confirmed HIV status and an HIV viral load and CD4 count within 6 months of recruitment. Patients were excluded if they were pregnant, had an allergy or other contraindication to use of iohexol or iodine, recent acute kidney injury, had cognitive or physical impairments or were on cimetidine. Patients were recruited who were and who were not on tenofovir as well as those with higher levels of serum creatinine.