Proteinuria and Bilirubinuria as Potential Risk Indicators of Acute Kidney Injury during Running in Outpatient Settings

Background and objectives: The purpose of this study was to explore which urinary markers could indicate acute kidney injury (AKI) during prolonged trail running in outpatient settings. Materials and Methods: Twenty-nine experienced trail runners (age 39.1 ± 8.8 years, weight 71.9 ± 11 kg, height 171.9 ± 8.3 cm) completed a 35 km event (cumulative positive ascend of 1815 m, altitude = 906 to 1178 m.a.s.l.) under a temperature of 25.52 ± 1.98 °C and humidity of 79.25 ± 7.45%). Two participant groups (AKI = 17 and No-AKI = 12) were made according to AKI diagnosis criteria based on pre- and post-race values of serum creatinine (sCr) (an increase of 1.5 times from baseline). Blood and urinalysis were performed immediately pre- and post-race. Results: Pre- vs. post-race differences in sCr and sBUN were found in both AKI and No-AKI groups (p < 0.01). Differences in post-race values were found between groups (p = 0.03). A total of 52% of AKI runners presented significant increases in proteinuria (χ(2) = 0.94, p = 0.01) and 47% in bilirubinuria (χ(2) = 0.94, p = 0.04). Conversely, No-AKI participants presented no significant increases in urine markers. Conclusions: These study’s findings may suggest the potential use of urinalysis as an accessible alternative in the outpatient setting to early identify transitional AKI until a clinical confirmation is performed.