Tehran University of Medical Sciences International Journal of Occupational Hygiene 2008-5109 17 2 2025 12 09 96 107 Elham Akhlaghi Pirposhteh Department of Occupational Health and Safety Engineering, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran Mohammad Javad Jafari Safety Promotion and Injury Prevention Research Center (SPIPRC), Shahid Beheshti University of Medical Sciences, Tehran, Iran Soheila Khodakarim Department of Biostatistics, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran Atefeh Mohammadinejad Department of Occupational Health and Safety Engineering, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran 2025 03 17 2025 05 11 Background: Iran’s hot and arid climate, combined with frequent exposure to heat-generating industrial processes, presents significant occupational health concerns. These environmental conditions may influence white blood cell (WBC) levels and their functions in response to heat stress. This study investigates the relationship between the Wet Bulb Globe Temperature (WBGT) index and WBC levels among workers in a foundry setting. Methods: This descriptive-analytical study was conducted on 55 male workers from two sections of a foundry: the cast iron section (35 participants) and the CNC section (20 participants). Blood samples were collected from all participants. Heat stress was assessed using the WBGT index. Intervening parameters—such as noise, lighting, and metabolic rates—were measured for each work group. Data analysis was performed using SPSS version 16. Results: In the case group, a decrease in total WBC count and lymphocyte levels was observed, along with an increase in neutrophil levels and the neutrophil-to-lymphocyte ratio. No significant relationship was found between heat stress and the composition of other WBC types, including basophils, monocytes, and eosinophils. Correlation analysis revealed strong associations between the WBGT index and total WBC count (R² = 0.93), neutrophils (R² = 0.85), lymphocytes (R² = 0.81), and overall WBC composition (R² = 0.82). Conclusion: Chronic exposure to heat stress may lead to significant alterations in WBC levels, potentially weakening and suppressing the immune system. The blood parameters examined in this study can serve as biomarkers affected by heat stress and merit further investigation. https://ijoh.tums.ac.ir/index.php/ijoh/article/view/680 https://ijoh.tums.ac.ir/index.php/ijoh/article/download/680/865