Characteristics of runners meeting acute kidney injury criteria following a 161‐km ultramarathon

The incidence of acute kidney injury (AKI) associated with ultramarathon running is varied partially because onsite measurement of serum creatinine concentration (Cr) is rarely performed at races due to logistical challenges. We conducted a prospective observational study using blood samples from volunteer athletes before and immediately after the Leadville Trail 100 Run in August 2014. The goals of our study were to determine the incidence of those meeting the AKI criteria immediately following the ultramarathon race and to evaluate the utility of using medical equations to back‐calculate creatinine levels for runners without known baseline creatinine levels and to identify possible risk factors for developing AKI. We were able to collect pre‐race and post‐race blood samples on 64 and 84 volunteers, respectively. AKI was defined as a Cr increase (≥1.5 times or ≥0.3 mg/dl from baseline). Of the 37 runners for whom we had both pre‐ and post‐race blood samples, 18 (49%) met the criteria for AKI. Using two different methods of back‐calculating baseline estimated creatinine (a fixed eGFR [estimated glomerular filtration rate] and an aged‐based eGFR), 6 (16%) and 22 (59%) of 37 runners met the criteria for AKI, respectively. We found that there is no accurate way to estimate baseline Cr in this population.