Objective: Examine whether the acute kidney injury (AKI) commonly observed among ultramarathon participants places the individual at risk for subsequent AKI of worse magnitude.
Setting: Western States Endurance Run.
Participants: Race finishers with postrace blood studies.
Independent variable: Acute kidney injury after 1 race.
Main outcome measures: Extent of AKI in subsequent race.
Results: Among 627 finishes in which serum creatinine values were known, 36.2% met "risk" or "injury" criterion with this group characterized by having faster finish times, greater body weight loss during the race, and higher postrace serum creatine kinase and urea nitrogen concentrations when compared with those not meeting the criteria. We identified 38 runners who had undergone postrace blood analyses at multiple races among which 16 (42.1%) met the risk or injury criterion at the first race. Of those 16 runners, 12 (75%) met the criteria at a subsequent race, an incidence that was higher (P = 0.0026) than the overall 36.2% incidence. For most (56.2%) of the 16 runners meeting the criteria at the first race, the subsequent race caused less increase in serum creatinine concentration and decrement in estimated glomerular filtration rate than the first race.
Conclusions: Mild AKI is common in 161-km ultramarathons, but there was no evidence that previous AKI caused greater renal dysfunction from a subsequent exercise stimulus of similar magnitude. This offers some reassurance to runners and their physicians that mild to moderate AKI in the setting of an ultramarathon is not cumulative or without complete recovery of kidney function when stressed.