Rapid reversal of acute kidney injury and hospital outcomes: a retrospective cohort study.

Background: Acute kidney injury (AKI), defined as an increment in serum creatinine level of 0.3 mg/dL or greater in 48 hours, is associated with poor outcomes. The prognosis associated with an increased creatinine level, either on admission or that develops in the hospital (ie, AKI), that rapidly returns to normal is not known.

Study Design: Retrospective cohort study.

Setting & Participants: 6,033 patients admitted to medical wards of a community teaching hospital between 2005 and 2007.

Predictor: AKI was defined as an increase in serum creatinine level of 0.3 mg/dL or greater within 48 hours. Increased serum creatinine level on admission was defined as serum creatinine greater than1.2 mg/dL on hospital admission in patients who did not subsequently meet criteria for AKI. Patients with a serum creatinine level of 1.2 mg/dL or less who had no increase of 0.3 mg/dL or greater within 48 hours during their hospital stay served as controls.

Outcomes & Measurements: Mortality, length of stay, intensive care unit transfer, and discharge destination were outcomes of interest.

Results: Of 6,033 patients, 735 had AKI. Of these, 443 (60%) had serum creatinine levels that subsequently decreased by 0.3 mg/dL or greater within 48 hours and 197 returned to normal levels within 48 hours. Overall, patients with AKI had significantly greater mortality rates (14.8%) than patients without AKI with increased serum creatinine levels on admission (2.5%) and controls (1.3%; P < 0.001). Patients with AKI with a serum creatinine level that returned to normal within 48 hours had substantially greater mortality rates (14.2%) than those who initially presented with an increased serum creatinine level on admission and subsequent serum creatinine level decrease of 0.3 mg/dL or greater to normal within 48 hours (2.5%; P < 0.01).

Limitations: Sample sizes of subgroups were small. Causes of AKI and increases in serum creatinine levels on admission were not assessed.

Conclusions: An increase in serum creatinine level of 0.3 mg/dL or greater during 48 hours of hospitalization predicts outcomes even if the value returns to normal. Patients who present to the hospital with an increased creatinine level that returns rapidly to normal have outcomes approaching those with serum creatinine levels consistently in the normal range.