Timing of Recovery From Moderate to Severe AKI and the Risk for Future Loss of Kidney Function.

Rationale & Objective: The extent of recovery of kidney function following acute kidney injury (AKI) is known to be associated with future chronic kidney disease. Less is known about how the timing of recovery affects the rate of future loss of kidney function.

Study Design: We performed a retrospective cohort study examining the independent association between the timing of recovery from moderate to severe AKI and future loss of kidney function.

Setting & Participants: 47,903 adult US veterans with stage 2 or 3 AKI who recovered to within 120% of baseline creatinine level within 90 days of peak injury.

Exposure: The timing of recovery of kidney function from peak inpatient serum creatinine level grouped into 1 to 4, 5 to 10, 11 to 30, and 31 to 90 days.

Outcome: A sustained 40% decline in estimated glomerular filtration rate below that calculated from the last serum creatinine level available during the 90-day recovery period or kidney failure (2 outpatient estimated glomerular filtration rates<15mL/min/1.73m, dialysis procedures > 90 days apart, kidney transplantation, or registry within the US Renal Data System).

Analytical Approach: Time to the primary outcome was examined using multivariable Cox proportional hazards regression.

Results: Among 47,903 patients, 29,316 (61%), 10,360 (22%), 4,520 (9%), and 3,707 (8%) recovered within 1 to 4, 5 to 10, 11 to 30, and 31 to 90 days, respectively. With a median follow-up of 42 months, unadjusted incidence rates for the kidney outcome were 2.01, 3.55, 3.86, and 3.68 events/100 person-years, respectively. Compared with 1 to 4 days, recovery within 5 to 10, 11 to 30, and 31 to 90 days was associated with increased rates of the primary outcome: adjusted HRs were 1.33 (95% CI, 1.24-1.43), 1.41 (95% CI, 1.28-1.54), and 1.58 (95% CI, 1.43-1.75), respectively.

Limitations: Predominately male population, residual confounding, and inability to make causal inferences because of the retrospective observational study design.

Conclusions: The timing of recovery provides an added dimension to AKI phenotyping and prognostic information regarding the future occurrence of loss of kidney function. Studies to identify effective interventions on the timing of recovery from AKI are warranted.