Suicide and suicide attempts continue to be an important public healthcare concern (Benton, 2022; Mpofu et al., 2023). It has been reported by the World Health Organization that suicide attempts amount to approximately 16 million, and each year, an estimated 800.000 people die as a result of suicide attempts health (Organization, 2018). Suicide is the second most common cause of death between the ages of 10–24 (Lindsey et al., 2019; Sheftall et al., 2022; Yard et al., 2021). Suicide and suicide attempt is a complex concept that cannot be explained by one single reason and is very difficult to predict (Benton, 2022). It has been reported that more than one factor such as biological, genetic, environmental factors, familial factors, gender, age, personality traits, culture, geography, medical diseases, mental diseases, addictions, and psycho-social stress factors play roles in the etiology of suicide and suicide attempts (Turecki and Brent, 2016).

The role of inflammation has been investigated in the pathophysiology of suicide attempts in recent years. The measurement of cytokines in plasma and cerebrospinal fluid (CSF) of people who have attempted suicide is the most commonly used method to examine inflammatory processes in this field. (Lindqvist et al., 2009; Miná et al., 2015). However, most of these measurements are costly or difficult to use for routine examination purposes. For this reason, peripheral inflammation parameters have been investigated in recent years to evaluate the pathophysiology and severity of psychiatric patients. Neutrophil/Lymphocyte Ratio (NLR), Monocyte/Lymphocyte Ratio (MLR), Platelet/Lymphocyte Ratio (PLR), Basophil/Lymphocyte Ratio (BLR), Eosinophil to Lymphocyte Ratio (ELR), Neutrophil/Albumin Ratio (NAR), and Systemic Inflammation Index (SII), Red Cell Distribution Width (RDW), RDW-Standard Deviation (RDW-SD), RDW-Coefficient of Variation (RDW-CV), Mean Platelet Volume (MPV), Plateletcrit (PCT), and Platelet Distribution Width (PDW) parameters are used to evaluate peripheral chronic inflammation. Also, leukocyte (neutrophil, eosinophil, monocyte, basophil, lymphocyte), erythrocyte, and platelet counts evaluated by complete blood count might be used as inflammation markers (Kara et al., 2019).

It has been shown that peripheral chronic inflammation plays roles in the etiology of many mental diseases such as Bipolar Affective Disorder (BAD), Major Depressive Disorder (MDD), schizophrenia, and substance use disorder, and is associated with some clinical parameters (Demir et al., 2021; Kaya et al., 2023; Özsoy et al., 2021; Taşci and Özsoy, 2023). There is a study in the literature reporting that NLR values were increased in patients who attempted suicide (Ayhan et al., 2019). In the literature, peripheral inflammation parameters have been the most emphasized in recent years in the studies conducted to investigate the etiology of mental disorders (Demir et al., 2021; Kaya et al., 2023; Özsoy et al., 2021; Taşci and Özsoy, 2023). It has been shown that peripheral chronic inflammation plays roles in the etiology of many mental diseases such as Bipolar Affective Disorder (BAD), Major Depressive Disorder (MDD), schizophrenia, and substance use disorder, and is associated with some clinical parameters (Demir et al., 2021; Kaya et al., 2023; Özsoy et al., 2021; Taşci and Özsoy, 2023). There is a study in the literature reporting that NLR values were increased in patients who attempted suicide (Ayhan et al., 2019).

Under stressful situations, the physiological response of leukocytes such as inflammation is an increase in the number of neutrophils and a decrease in the number of lymphocytes. In a study investigating the relationship between inflammation parameters and possible biomarkers of suicide, it was found that dysregulation of HPA axis activity affects inflammatory pathways and thus increases the risk of suicide (Berardelli et al., 2020). There are also studies showing a frequent connection between inflammatory parameters and psychological distress, hopelessness and demoralization (Costanza et al., 2022). Also, the sympathetic nervous system is activated in the presence of chronic stress, platelets increase and endothelial permeability is induced. When such a permeability occurs, neutrophils and macrophages emerge and cause peripheral inflammation. It was reported in previous studies that elevated MLR values are associated with the overexpression of immunological genes that increase the production of monocyte-related cytokines and consequently activate microglia as a marker of neuroinflammation (Zheng et al., 2022). Also, as a biomarker, the importance of the NAR Index in the presence of inflammation has increased in recent years in predicting prognosis along with SII, which combines neutrophil, platelet, and lymphocyte counts, as a new marker reflecting the balance between immune and inflammatory states. SII was used as a marker of subclinical inflammation and prognosis in some previous studies (Zhang et al., 2019). Hemoglobin, hematocrit, White Blood Cell, erythrocyte, RDW, RDW-CV, RDW-SD, MPV, and PDW values are less investigated parameters to evaluate inflammation. Thrombocytosis and/or increase in platelet volume indicates platelet reactivity. Reactive platelets also play roles in inflammation (Yuri Gasparyan et al., 2011). Platelet activity and reactivity are evaluated with MPV and PDW. PDW value is more specific than MPV in showing platelet activity. RDW is usually reported as two different values (RDW-CV and RDW-SD). Recent studies focus on the relationship between RDW, RDW-SD, and RDW-CV and the chronic inflammatory process (Seretis et al., 2013).

It is of great importance to determine the possible risk factors of suicidal behavior, which is a public health problem today, and to take measures to prevent suicidal behavior. As stated in the literature, this study was planned to be conducted with the hypothesis that there may be changes in inflammatory parameters in individuals who have attempted suicide. Additionally, no study has been found in which all these chronic inflammation parameters were evaluated together. Based on this information, the purpose of the present study was to compare and evaluate the peripheral inflammation markers (the number of white blood cells, hemoglobin, hematocrit, platelet, and leukocyte subgroups) and NLR, MLR, PLR, BLR, ELR, SII, NAR, MPV, PDW, PCT, RDW, RDW, SD and RDW-CV indices in patients who attempted suicide with healthy controls.