Mechanism of Acute Kidney Injury in Mild to Moderate Heat-related Illness.

Objectives: This study focuses on mild-to-moderate severity cases to examine the triggers initiating kidney injury.

Materials: Patients aged ≥18 years with suspected heat-related illnesses at the Juntendo University Hospital Emergency and Primary Care Center between July and September 2020 and June and August 2022 were included.

Methods: Blood samples were obtained during their visit, and the patients were categorized into two groups based on their cystatin-based estimated GFR (eGFRcys) values: a kidney injury group (eGFRcys < 60 mL/min/1.73 m²) and a non-kidney injury group (eGFRcys ≥ 60 mL/min/1.73 m²). Inflammation, coagulation, and skeletal muscle damage markers were compared between the groups, and markers related to the early development of kidney injury were examined.

Results: Thirty-five patients were diagnosed with heat-related illnesses, and 10 were diagnosed with kidney injury. White blood cell count was higher in the kidney injury group (P < 0.01), whereas the levels of CRP and Interleukin-6 showed no significant difference between the groups. No statistically significant differences in coagulation markers were observed. In contrast, myoglobin, a marker of skeletal muscle damage, showed elevated levels in the kidney injury group (r = -0.80, P < 0.01) and demonstrated a stronger association with early kidney injury than creatine kinase (r = -0.38, P < 0.05).

Conclusions: The predominant mechanism of acute kidney injury in mild to moderate heat-related illnesses appears to be tubular damage caused by myoglobin. Measuring myoglobin levels is essential to identify and exclude patients at risk of acute kidney injury due to heat-related illnesses.