Objective: To assess whether GFR measurement using 4-phase CT urography is reliable in patients with GFR below 60 ml/min/1.73 m², as compared with iohexol clearance (reference method): - Unbiased (mean difference between CT-measured GFR and iohexol clearance not different from zero). - and accurate: at least 50% and 80% of GFR values measured by CT urography within 10% and 20% of biological clearance values for iohexol clearance.
Method: Single-center interventional study. After performing a 4-phase CT urography (or 3-phase CT scan, with the addition of a 4th phase for research purposes), performed for clinical indications as part of the patient's care, and using iohexol as a contrast agent, patients will undergo a biological measurement of iohexol clearance, based on serum and urine samples taken over 4 periods of 1 hour, between 3 and 7 hours after the CT scan. No iohexol will be reinjected to measure GFR. The CT scan images will be segmented by the investigator to determine the CT-measured GFR.
The inclusion criteria are: - Patients older than 18 years of age - Having given written consent to participate in the study. - Patient referred to the medical imaging department of the Henri Mondor University Hospital for a 3-phase or 4-phase abdominal CT scan. - With an estimated GFR according to CKD-EPIcreat2009 \< 60 ml/min/1.73m² - Hospitalized or outpatient. - Affiliated with French national health insurance.
The exclusion criteria are: - Patients with hip implants, due to artifacts that make quantification of the contrast agent in the bladder unreliable. - Lack of health insurance - Patients under legal protection.
