Having one kidney not an independent risk factor in contrast CT

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 - Safety First

Common sense assumptions backed by ACR guidelines deem one-kidney patients a higher risk for kidney injury from iodinated contrast media, but a study published ahead of print in Radiology suggests the heightened caution is unwarranted.

Jennifer McDonald, PhD, of Mayo Clinic and colleagues retrospectively analyzed outcomes of propensity-matched patients who underwent contrast-enhanced CT at Mayo from 2004 to 2013.

The solitary-kidney cohort comprised 247 patients; 691 patients had both their kidneys.

All underwent an IV contrast-enhanced abdominal, pelvic or thoracic CT scan and had at least two prescan (24 hours prior) serum creatinine (SCr) results and at least one postscan (24–72 hours postscan) SCr result.

McDonald and team found the rate of contrast-induced nephropathy—acute kidney injury (AKI) following the administration of iodinated contrast media—similar between the two groups when compared by creatinine clearance: 

Solitary kidney cohort: AKI definition increase in serum creatinine [SCr] level ≥ 0.5 mg/dL odds ratio = 1.11 [95 percent confidence interval {CI}: 0.65, 1.86], P = .70

Bilateral kidneys cohort: AKI definition increase in SCr level ≥ 0.3 mg/dL or 50 percent over baseline odds ratio = 0.96 [95 percent CI: 0.41, 2.07], P = .99

The rate of emergent dialysis, while rare across the board, was also similar between cohorts.

Additionally, although the rate of mortality was higher in the solitary kidney group, a chart review showed that most deaths owed to cancer—and none was caused by AKI.

In their study discussion, the authors note that their propensity-matched cohort drew from a largely inpatient population that is probably at higher risk than outpatient populations for contrast-induced nephropathy.

“However, this decreased risk in the outpatient population would result in lower rates of AKI, emergent dialysis and mortality compared with the inpatient population and would require a substantially larger sample size to be sufficiently powered to compare solitary and bilateral kidney groups," wrote McDonald and colleagues. "We acknowledge the lack of power in our study and emphasize the need for additional studies.”

That said, the authors conclude that contrast-enhanced CT protocols can be safely guided “by means of image optimization rather than contrast-induced nephropathy risk in patients with a solitary kidney.”