Author(s): PALIN, T., STACEY, M., WAINWRIGHT, B., SNAPE, D., ALLENBY-DILLEY, O., PARSONS, I., O'HARA, J., WOODS, D., Institution: LEEDS BECKETT, Country: UNITED KINGDOM, Abstract-ID: 2026

INTRODUCTION:
The kidney is subject to conflicting processes during adaptation to elevated altitude (diuresis and natriuresis) and environmental heat (water and sodium retention). Athletes and military personnel who are transported rapidly from lower, cooler locations to hotter, higher settings may experience reduced physical performance and increased risk of acute kidney injury (AKI). Liver fatty acid-binding protein (L-FABP) is a novel AKI marker that rises with the severity of organ injury (1) in the heat and is also released with hypoxia (2); values >12.5 ng/mL indicate increased AKI risk (1). We tested the hypothesis that, under the combined climatic challenge of increased altitude and heat, urinary L-FABP would be relatively increased.
METHODS:
Twenty-seven military personnel were deployed, by air then road, from sea level in the UK to increased altitude (1947 m) and heat (daytime wet bulb globe temperature, WBGT, 24.4 ± 1.98 °C) in Kenya. They were rested upon arrival (Day 0), then commenced seven days of structured, progressive acclimatisation. Fluids were taken ad libitum. Urine was sampled at rest on Day 0, 2 and 7, for measurement of specific gravity (SG) and Point-of-Care (POC) assay of L-FABP (Renischem, Tokyo). Heart rate (HR) and peripheral oxygen saturations (SpO2) were sampled and urinary measures repeated following exercise on Day 2 (50 min walking at 6 km/h, WBGT 21.5 °C) and Day 7 (100 min at 6 km/h, additional 10 kg load carriage, WBGT 24.8 °C).
RESULTS:
Resting urinary values did not change for SG, whereas L-FABP increased from Day 0 to Day 2 and Day 7 (1.0 [0.3, 2.1] vs 2.7 [0.7, 3.6] vs 1.8 [0.8, 4.3], P=0.002). From Day 2 to Day 7, post-exercise HR and SpO2 decreased significantly (89 ± 14 vs 77 ± 14 bpm, P<0.001, and 96 ± 2 vs 94 ± 1 %, P=0.021). Main effects of exercise were evident for SG, which increased significantly from pre-to-post (P=0.009), and for L-FABP, which showed a significant reduction (P=0.002). The impact of exercise on L-FABP was consistent with acclimatisation (P=0.836), whereas the rise in SG on Day 2 (P=0.002) was not observed on Day 7 (P=0.721), with post-exercise SG on Day 7 lower than on Day 2 (P=0.036). L-FABP did not exceed the AKI risk threshold.
CONCLUSION:
Short-term acclimatisation associated with increased renal stress at rest. Despite increasing duration of exercise, additional load and higher WBGT, the impact of exercise on SG diminished, suggested improved water/electrolyte handling as an adaptive mechanism. Assay of L-FABP at POC provided assurance that structured acclimatisation to altitude and thermal stress associated with a low risk of AKI.
REFERENCES:
1. Goto, et al. (2025) Liver fatty acid-binding protein point-of-care testing detects heat-induced organ damage: a pilot study in Japanese male self-defense force personnel. Sci Rep, 15: 7197.
2. Katagiri D, et al. (2023) Urinary L-Type Fatty Acid-Binding Protein Predicts Oxygen Demand of COVID-19 in Initially Mild Cases. Crit Care Explor. Mar 9;5:e0873.