Assessment and Comparison of Markers of Inflammation and the Systemic Immune–Inflammation Index in Patients with Major Depressive Disorder and Healthy Controls at SMS Medical College, Jaipur: An Observational Case–Control Study

Background: Major depressive disorder (MDD) is increasingly recognized as a disorder with neuroimmune components, where low-grade systemic inflammation may influence neurotransmission, neuroendocrine function, and neuroplasticity. Cell count–derived indices such as the neutrophil-to-lymphocyte ratio (NLR), platelet-tolymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), and systemic immune-inflammation index (SII) are inexpensive and clinically scalable surrogate markers of systemic inflammatory status. Evidence regarding these markers in major depressive disorder has been inconsistent; meta-analytic studies suggest that NLR is often elevated in depression, whereas findings for PLR and MLR remain variable and inconclusive. Methods: An observational case control study was done at the Psychiatric centre, SMS medical college, Jaipur, Rajasthan, India, during the period October 2024 and August 2025. Adults aged 18-60 years who had MDD according to DSM-5-TR were recruited consecutively (screened n=72; analyzed n=65). Healthy controls after screening by Mini-interview of International Neuropsychiatry Interview (MINI, version 7.0.2) (screened n=85; analyzed n=65). Participants who had systemic illnesses, were pregnant, or taking anti-inflammatory, immunomodulatory and antibiotic medications were excluded. Absolute neutrophil count (ANC), absolute lymphocyte count (ALC), absolute monocyte count (AMC), ESR, NLR, PLR, MLR and SII were determined from peripheral blood. Group comparisons were conducted using appropriate parametric/non-parametric metrics testing procedures (α=0.05) Results: A total of 130 participants were included in the analysis (65 MDD; 65 controls). Mean age in MDD (31.79±9.72) was higher as compared to controls (22.19±6.65; p=0.02). There was no difference in sex distribution (female 44 vs 43 p=0.99). MDD subjects had numerically higher ANC (5077±1856 vs 4503±2655), AMC (416±211 vs 333±309), NLR (2.54±1.64 vs 1.93±0.57) and ESR (21.51±19.10 vs 9.20±6.45). However, none of the inflammatory indices showed statistically significant between-group differences. Conclusion: In this sample collected at a hospital, various peripheral indicators of inflammation were trending towards an increase in MDD, but results were not statistically significant, possible reasons include limited statistical power, age mismatch between groups, and single-time-point sampling.