Glomerular Filtration Predicts Mortality After AAA Repair

BY Mark S. Lesney

CHICAGO -- Glomerular filtration rate is a better indicator than serum creatinine for subclinical renal dysfunction and for predicting postoperative mortality after abdominal aortic aneurysm repair, said Ali Azizzadeh, M.D., at the Vascular Annual Meeting.

Renal disease is a known risk factor for mortality after aneurysm repair. Renal dysfunction is traditionally evaluated preoperatively using serum creatinine as a surrogate marker for at-risk patients. However, serum creatinine level is affected by muscle mass, hydration status, and glomerular filtration rate (GFR), making it questionable as the best indicator of renal function, said Dr. Azizzadeh, medical director of the vascular laboratory at Memorial Hermann Hospital, Houston.

Dr. Azizzadeh, along with colleagues at the Washington University in St. Louis, conducted a retrospective study of 398 patients (340 of whom were men) who underwent endovascular abdominal aortic aneurysm repair using the AneuRx device between 1999 and 2004.

Patients were divided into quartiles based on preoperative GFR: I (7-44), II (45-60), III (61-79), and IV (80 or more), using the Cockcroft and Gault equation, which relies on age, body weight, and serum creatinine to calculate GFR. For women, the calculated GFR is multiplied by a factor of 0.85, based on the assumption of less muscle mass per body weight.

The investigators estimated survival using the Kaplan-Meier method and compared the results with an accepted criterion of abnormal renal function (serum creatinine more than 1.7 mg/dL). Survival at 48 months was 58%, 67%, 86%, and 82% for GFR quartiles I-IV, respectively, with quartile I being significantly worse than the other three throughout the follow-up period.

GFR proved a highly significant predictor of mortality compared with creatinine, which failed to reach significance. Overall, a 2% reduction in mortality was shown for every point increase in GFR.

"There was only one patient in the entire study who had an abnormal creatinine but a normal GFR," Dr. Azizzadeh said. "This was probably due to the very large body mass of this patient. We found that 18% of patients had an abnormal creatinine, compared with 83% who had an abnormal GFR."

Thus, GFR is more sensitive than creatinine for detecting subclinical renal disease, and "it is a more accurate predictor of perioperative and long-term mortality following endovascular aortic aneurysm repair," he said.

Patients should have GFR screening before abdominal aortic aneurysm repair, and high-risk patients should be informed of their risk status. "These patients may most benefit from the use of alternative contrast agents and periprocedural renal protection techniques," Dr. Azizzadeh concluded.