Accuracy of Estimated Creatinine in Multistage Ultramarathon Runners

Abstract

Introduction-Ultramarathon running is increasing in popularity worldwide, as is the growing body of research on these athletes. Multiple studies have examined acute kidney injury through estimated baseline creatinine (Cr) and glomerular filtration rate (GFR). Values are estimated through an age-based formula of GFR and the modification of diet in renal disease (MDRD) equation. However, the accuracy of this practice in a cohort of healthy athletes is unknown.Methods-A prospective analysis of the first 40-km (25-mi) stage of 6-stage 250-km (155-mi) multistage ultramarathons in the Sahara, Namibia, Atacama, and Gobi Deserts. Runners had prerace measured baseline Cr compared to estimated values through age-based estimated GFR and back calculation of Cr through the MDRD equation.Results-Forty-eight participants (27% female, age 39 §10 y) had Cr values analyzed. The mean measured Cr was 0.99 §0.17, which was 11% higher than an estimated Cr of 0.88 §0.14 (P<0.01). Estimated age-based GFR was 95.9 §5.8 mLÁmin ¡1 compared to GFR based on measured Cr and MDRD of 86.1 §14.6 (P<0.001).Conclusions-Estimated values of GFR and Cr by standard age-based values and MDRD equation were significantly inaccurate, which would overinflate the incidence of acute kidney injury. Future studies should devise a new model for estimation of baseline Cr that is validated in this population.

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

“…This work demonstrates a basic methodological issue with estimation of baseline eCr (estimated Cr) in healthy runners for use in determining post‐race AKI. This problem has been previously commented upon 7,10,11,31‐33 . We used two different methods, which showed overestimation and underestimation of the number of runners meeting AKI criteria.…”

“…As it is impractical to obtain baseline blood samples on all runners before a race, there are many different ways that have been used to estimate the baseline Cr or GFR. Most studies on ultramarathon runners have used an age‐based estimation of GFR (100 mL/min for individuals ≤40 years of age and 140‐age for individuals >40 years of age) 10,11,19,30 . Then the baseline Cr was back‐calculated by rearrangement of the modified diet in renal disease (MDRD) equation:…”

“…Most equations for estimating GFR are based on the general population and hospitalized individuals 6‐9 . There is a lack of data on the normal GFR range among healthy ultramarathon runners 10 . AKI is relatively common in ultramarathon competitors, with documented incidence being 25%‐80% 10‐14 .…”

“…There is a lack of data on the normal GFR range among healthy ultramarathon runners 10 . AKI is relatively common in ultramarathon competitors, with documented incidence being 25%‐80% 10‐14 . Fluid and electrolyte disturbances, hemolysis and skeletal muscle damage can occur during long‐distance running and a combination of dehydration, heat stress, muscle injury, and non‐steroidal anti‐inflammatory drugs (NSAIDs) use may all contribute to the development of AKI 15‐18 .…”

Changes in Water Soluble Uremic Toxins and Urinary Acute Kidney Injury Biomarkers After 10- and 100-km Runs

“…Another problem is that the baseline values of creatinine, before kidney injury, are unknown. So-called back calculation is not precise and seems to be highly inadequate in exercising persons [11]. Therefore, diagnosis of AKI cannot be based on relative changes of creatinine level, which is the most rational and consistent with KDIGO [7].…”