Abstract
Introduction: One of the key mechanisms affecting mortality and morbidity in intensive care unit (ICU) patients is oxidative stress and the accompanying antioxidant defense system. The Platelet Mass Index (PMI) has been proposed as a novel parameter associated with both disease severity and inflammation. This study sought to explore the association between platelet mass index (PMI) and the levels of total oxidant status (TOS), total antioxidant status (TAS), and oxidative stress index (OSI) in patients admitted to the intensive care unit.
Materials and Methods: This prospective study included 152 patients hospitalized in the ICU and 60 healthy individuals as the control group. Blood samples were analyzed to determine TOS, TAS, procalcitonin (PCT), ferritin, C-reactive protein (CRP), mean platelet volume (MPV),white blood cell count (WBC) and platelet count (PLT). Platelet mass index (PMI) was calculated using PLT and MPV values, while OSI was calculated using TOS and TAS results. The obtained data were analyzed statistically.
Results: Among ICU patients, levels of PMI, CRP, TOS, and OSI were elevated, while PLT and TAS levels were reduced compared to the control group. No significant clinical correlation was observed between PMI and the other measured variables.
Conclusion: PMI may serve as a simple and easily calculable biomarker reflecting oxidative stress levels in ICU patients. These findings suggest that PMI could be used as a supportive parameter for evaluating oxidative stress in intensive care practice.

Key words: Platelet Mass Index, total oxidant status, total antioxidant status, oxidative stress index