M.R. Gradow, C.L. Chapman, S.M. Holt, H.N. Medved, J.A. Yep, W.A.B. Howells, S.C. Brazelton, C.T. O’Connell, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM

University of Oregon, Eugene, OR, USA

(Award Winner)

Hypohydration increases hospitalizations for acute kidney injury (AKI) during extreme heat events. A barrier to accurate self-monitoring of hydration status includes the impracticality of invasive methods. The 8-point urine color scale is a non-invasive assessment with potential use as a low-cost screening tool for elevated AKI risk during prolonged hypohydration. The AKI risk score (AKIrisk) has a U.S. Food and Drug Administration approved indication to screen for the risk of developing moderate-to-severe AKI. AKIrisk is calculated from the product of urinary insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 ([IGFBP7∙TIMP-2]). PURPOSE: To determine the diagnostic accuracy of the 8-point urine color scale in assessing AKIrisk in healthy young males and females during prolonged mild hypohydration. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females, 11 males; 21(3) years] completed 24 hours of fluid deprivation to induce hypohydration or 24 hours normal fluid consumption to remain euhydrated. Protocols were separated by ³72 hours. Spot morning urine samples were collected immediately following each 24-hour protocol. Urine color was assessed using a validated 8-point visual scale by three independent investigators. AKIrisk was determined by urinary [IGFBP7∙TIMP-2] >0.3 (ng∙ml-1)2∙1000-1 via enzyme-linked immunosorbent assay. Contingency analyses were performed to calculate positive and negative predictive values for urine color ≥3, ≥4, and ≥5 a.u. in predicting AKIrisk. Data are presented as mean with 95% confidence intervals. RESULTS: Fisher’s exact test revealed an association between AKIrisk >0.3 (ng∙ml-1)2∙1000-1 and urine color ≥3 (P<0.0001), but no association with urine color ≥4 or ≥5 a.u. (P≥0.1327). The positive predictive value and negative predictive value for urine color ≥3 a.u. in predicting AKIrisk >0.3 (ng∙ml-1)2∙1000-1 were 0.91 (0.72, 0.98) and 0.73 (0.52, 0.87). CONCLUSION: These data indicate that values of three or greater on the 8-point urine color scale have excellent positive predictive value for AKIrisk and lend preliminary support for the utility of the color scale as a rudimentary screening tool during prolonged mild hypohydration.

Supported by NIH R01HL144128 and F32HL164021.

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