Major Database May Underestimate AKI Prevalence

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SAN DIEGO—A large surgical database may be missing many cases of acute kidney injury (AKI), according to a recent study.

An analysis of data from the American College of Surgeons' National Surgical Quality Improvement Program (ACS NSQIP) revealed that 93.2% of patients who did not meet the NSQIP criteria for AKI—an increase in serum creatinine of at least 2 mg/dL or acute renal failure necessitating dialysis—actually met one of the primary criteria for the RIFLE AKI ‘risk' category—an increase in serum creatinine of more than 50% or of at least 3 mg/dL in seven days.

Azra Bihorac, MD, Assistant Division Chief for Research in the Division of Critical Care Medicine at the University of Florida in Gainesville, and his colleagues examined data from 47,801 patients in the ACS NSQIP who had major surgery between 2000 and 2008. The ACS NSQIP is a prospective, peer-controlled, validated database designed to quantify 30-day, risk-adjusted outcomes for patients undergoing major surgical procedures.

The researchers excluded patients with category 5 chronic kidney disease on admission, baseline estimated glomerular filtration rate of below 65 mL/min/1.73 m2, patients with a transplant, trauma, or burn, and those with a serum creatinine clearance below 2 mg/dL, leaving a study population of 27,841 patients.

ASQIP identified 701 (2.5%) as having AKI, but 10,228 (36.7%) met the RIFLE AKI criteria, Dr. Bihorac reported at the Society for Critical Care Medicine's 2011 annual meeting. Thus, the NSQIP missed 93.2% of cases. Twenty-two percent of the overall patient group was in the RIFLE risk category, 9% in RIFLE injury, and 4% (993) in RIFLE failure.

All but three of the 701 people with AKI based on the NSQIP criteria were in the RIFLE failure category; the remaining three were in the RIFLE injury category.

Dr. Bihorac and her colleagues also demonstrated that the RIFLE criteria much more accurately discriminate between patients who are likely to die and suffer other delirious outcomes due to having AKI than do the ACS NSQIP criteria.

Other major societies also have AKI definitions that are widely divergent from those of RIFLE. For example, the American College of Surgeons' Committee on Trauma defines AKI after trauma as an increase in serum creatinine to above 3.5 mg/dL. The Society of Thoracic Surgeons' National Cardiac Surgery database defines AKI as serum creatinine above 2 mg/dL, a doubling of peak postoperative serum creatinine, or a requirement for dialysis.

Dr. Bihorac said she believes the findings from her study support the need for a change in these societies' guidelines. “These definitions all miss the earlier-stage and most prevalent forms of AKI,” she said.

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