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DIAGNOSTIC ACCURACY OF URINE COLOR IN PREDICTING ACUTE KIDNEY INJURY RISK SCORE DURING PROLONGED HYPOHYDRATION

Abstract

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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