Acute Kidney Injury Predisposes Elderly to Organ Failure
By Crystal Phend
MINNEAPOLIS, 23 nov 2008 -- Older adults who suffer an acute injury to the kidneys -- from trauma, surgery, or illness -- are at dramatically increased risk of later end stage renal disease (ESRD).
Patients who've suffered an injury and had no prior chronic kidney problems were 13 times more likely to develop ESRD than those who had not suffered an acute kidney injury (95% confidence interval 10.6 to 16.0), according to Allan J. Collins, M.D., of the U.S. Renal Data System Coordinating Center and the University of Minnesota, and colleagues.
The risk was 54% higher for those who suffered an acute kidney injury than for those with chronic kidney disease but no acute injury (hazard ratio 8.43), the researchers reported online in the Journal of the American Society of Nephrology.
Although acute kidney injury has generally been considered self-limiting, these findings, based on information from the Medicare database, suggested that episodes of acute problems may accelerate progression of renal disease, they said.
"Close medical follow-up of kidney function in elderly patients who have experienced acute kidney injury is warranted," Dr. Collins wrote.
But it's difficult to separate out the effects of acute kidney injury and chronic kidney disease, noted co-author Areef Ishani, M.D., also of the University of Minnesota and U.S. Renal Data System Coordinating Center.
Some of the risk may have been misattributed to acute injury if the administrative data missed chronic kidney disease among those with acute injury, he said.
Even if this were the case, though, the findings are clear that patients with acute kidney injury are at high risk, Dr. Ishani said.
In the researchers' analysis of a random 5% sample of Medicare beneficiaries in 2000, the incidence of acute kidney injury was 3.1% and 12.0% had baseline chronic kidney disease.
Acute kidney injury was also seen in 25.2% of ESRD patients based on records of the U.S. Renal Data System, a registry of end-stage patients treated at all renal dialysis units and transplant facilities.
Among the 233,803 patients 67 or older who were hospitalized for acute kidney injury without any prior injury or end stage renal disease, 5.3 per 1,000 developed end stage disease over the next two years.
The likelihood of initiating ESRD treatment through two years of follow up was:
6.96% for those with acute kidney injury overall
3.68% for those with only acute injury
2.54% for those with only chronic kidney disease
14.29% for patients with both acute and chronic kidney damage
0.25% for those with neither kind of kidney damage
After adjustment for chronic kidney disease and other factors like age, gender, diabetes, race, gender, and hypertension, patients with acute kidney injury were 6.74 times more likely to develop ESRD than those who had not had an injury.
When the two types of kidney damage were considered simultaneously, patients with only acute kidney injury were at 13-fold risk compared with 8.43-fold risk among those with only chronic kidney disease, a more than 50% difference.
Notably, patients who had pre-existing chronic kidney disease and sustained acute kidney injury "showed a striking multiplicative effect" on risk of ESRD compared with patients with neither diagnosis (HR 41.19).
The researchers cautioned, though, that the Medicare claim codes used to assess kidney conditions may have high specificity but low sensitivity, which would make the findings reliable but underestimate the complete impact of both acute and chronic kidney damage, especially among women and patients older than 75.
But if more severe acute kidney injury episodes were more likely to be documented in the codes, the observed association would have been potentially inflated, they added.
The databases used also did not allow adjustment for severity of acute or chronic kidney conditions, they said.
Although acknowledging that the increased incidence of ESRD associated with acute kidney injury may have been truly driven by underlying advanced chronic kidney disease, the investigators said the findings suggested that acute damage "may be an important factor contributing to the high incidence of ESRD in the United States."
The study was performed under contract with the National Institute of Diabetes and Digestive and Kidney Diseases.
The researchers reported no conflicts of interest.