Elevated Monocyte-to-Lymphocyte and Platelet-to-Lymphocyte Ratios Are Associated with Disease Activity and Pain in Fibromyalgia: A Cross-Sectional Study

<b>Objective:</b> This study aimed to evaluate blood count-derived inflammatory indices-the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), and the systemic immune-inflammation index (SII)-in patients with fibromyalgia and to explore their association with disease activity and pain severity. <b>Methods:</b> A cross-sectional study was conducted with 85 fibromyalgia patients and 84 age- and sex-matched healthy controls. Demographic, clinical, and laboratory data were recorded. Inflammatory indices were calculated from blood counts. Disease activity and functional status were assessed with the Fibromyalgia Impact Questionnaire (FIQ), Health Assessment Questionnaire (HAQ), and pain severity with the Visual Analog Scale (VAS). <b>Results:</b> Compared to controls, the fibromyalgia group had significantly higher BMI, PLR, MLR, and NLR (all <i>p</i> < 0.05), and lower lymphocyte levels. PLR and MLR moderately discriminated fibromyalgia (AUC = 0.623 and 0.661, respectively), suggesting limited diagnostic utility when used alone. MLR and BMI were independently associated with fibromyalgia in multivariate analysis. Disease duration showed significant positive correlations with PLR (r = 0.167), MLR (r = 0.228), FIQ (r = 0.773), HAQ (r = 0.589), and VAS at rest and movement (r = 0.584 and r = 0.601; all <i>p</i> < 0.05). PLR, MLR, and NLR were also positively correlated with VAS scores, while SII showed no significant associations. FIQ was strongly correlated with pain severity and HAQ with VAS during movement. <b>Conclusions:</b> Blood count-derived indices, particularly PLR and MLR, are elevated in fibromyalgia and are associated with disease duration, severity, and pain. Although PLR and MLR were higher in fibromyalgia patients, their discriminatory ability was limited and should be interpreted cautiously, indicating that their diagnostic specificity is low, as these ratios primarily reflect nonspecific inflammatory processes.