Creatinine clearance must be checked to reduce CIN

Many elderly patients scheduled for contrast-enhanced CT scans who have no reported risk factors may still be at risk of contrast-induced nephropathy (CIN). While measuring the creatinine levels is standard, it may be better to assess creatinine clearance as well, according to researchers at the VA North Texas Health Care System.

Dr. Mithilesh Kumar and Dr. Andre Duerinckx retrospectively reviewed the charts of 561 consecutive patients during a six-month period. The data consisted of responses to a questionnaire about hypertension, diabetes, renal disease, chemotherapy, serum creatinine levels, and estimated creatinine clearance.

Most patients were male (532), and the average age was 64 years. Nearly 60% of patients reported no known risk factors.

Fifteen percent (86) of patients had creatinine levels greater than 1.4 mg/dL and 12% (66) had levels greater than 1.5 mg/dL. Of these patients, 16% and 13%, respectively, reported no history of risk factors.

The numbers are similar for creatinine clearance. Thirteen percent of all patients had a clearance of less than 50 mL/min and 25% had clearance less than 60 mL/min. Nearly 19% and 22%, respectively, of these patients reported no risk factors.

Using a cutoff of 50 and 60 mL/min creatinine clearance, 20% of patients with no clinical risk factor would have been at increased risk of CIN. A cutoff of 1.4 and 1.5 mg/dL for patients with no risk factors would have placed 20% and 14% of them, respectively, at risk for CIN.

Creatine clearance takes into account a patient's weight and age. A person who is elderly and thin can have very low creatinine clearance even with nearly normal creatinine levels, said Duerinckx, now the director of MR, CT, and vascular imaging for Forsyth Radiological Associates in Winston-Salem, NC.

"These data allowed us to better negotiate with all the providers in the hospital, to show them that taking creatinine levels and creatinine clearance is a very reasonable thing to do," he said. "We should take joint responsibility as providers to do this as early as possible so we do not inconvenience the patients at the time of the CT scan."

The purpose is not just patient convenience but also to ensure healthy throughput in the CT suite, Duerinckx said. Oftentimes, patients scheduled for contrast-enhanced CT scans will not have creatinine tests. They must then go to the lab, where results can take up to three hours.

"With these data, it will be easier to get referring physicians to collaborate. They tend to minimize the potential of creatinine levels and clearance. With this hard data we can show them it is not an insignificant number of patients who could be put at risk," he said.