Diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive acute kidney injury risk following physical work in the heat

Abstract

Occupational heat stress increases the risk of acute kidney injury (AKI). This study presents a secondary analysis to generate novel hypotheses for future studies by investigating the diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive AKI risk following physical work in the heat in unacclimatized individuals. Unacclimatized participants (n = 13, 3 women, age: ∼23 years) completed four trials involving 2 h of exercise in a 39.7 ± 0.6 °C, 32 ± 3% relative humidity environment that differed by experimental manipulation of hyperthermia (i.e., cooling intervention) and dehydration (i.e., water drinking). Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Positive AKI risk was identified when the product of concentrations insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7∙TIMP-2] exceeded 0.3 (ng∙mL⁻¹)²∙1000⁻¹. Peak absolute core temperature had the acceptable discriminatory ability (AUC = 0.71, p = 0.009), but a relatively large variance (AUC 95% CI: 0.57–0.86). Mean body temperature, urine specific gravity, urine osmolality, peak heart rate, and the peak percent of both maximum heart rate and heart rate reserve had poor discrimination (AUC = 0.66–0.69, p ≤ 0.051). Mean skin temperature, percent change in body mass and plasma volume, and serum sodium and osmolality had no discrimination (p ≥ 0.072). A peak increase in mean skin temperature of >4.7 °C had a positive likelihood ratio of 11.0 which suggests clinical significance. These data suggest that the absolute value of peak core temperature and the increase in mean skin temperature may be valuable to pursue in future studies as a biomarker for AKI risk in unacclimatized workers.

Keywords:

• Exercise
• heat strain
• heat stress
• dehydration
• hypohydration
• AKI biomarker

Acknowledgments

We thank the volunteers who participated in this study. Conception and design: C.L.C., B.D.J., D.P.H., and Z.J.S.; performed experiments: C.L.C., Z.J.S.; analyzed data: C.L.C.; interpreted results of experiments: C.L.C., B.D.J., D.P.H., and Z.J.S.; prepared figures: C.L.C.; drafted manuscript: C.L.C.; edited and revised manuscript: C.L.C., B.D.J., D.P.H., and Z.J.S.; approved final version of manuscript: C.L.C., B.D.J., D.P.H., and Z.J.S.

Data availability

The data that support the findings of this study are available from the corresponding author, Z.J.S, upon reasonable request.

Ethics approval

This study was approved by the Institutional Review Board (STUDY00001746) at the University at Buffalo in accordance with the Declaration of Helsinki, except for registration in a database. Informed written consent was obtained from all participants prior to inclusion in this study.

Disclosure statement

Z.J.S. has received consultant fees from Otsuka Holdings Co., Ltd. Otherwise, no other potential conflicts of interest, financial or otherwise, are declared by the authors.

Disclaimer

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Army, the Department of Defense, or the U.S. government.

Additional information

Funding

This research was supported by awards from the U.S. Centers for Disease Control and Prevention (R01-OH-011528 to Z.J.S.), the Carl V. Gisolfi Memorial Fund from the American College of Sports Medicine (17-00580 to C.L.C.), and the Mark Diamond Research Fund from the University at Buffalo (SP-19-04 to C.L.C.).