Objectives

This study aimed to evaluate hematological inflammatory indices in patients with knee osteoarthritis and to investigate their association with radiographic disease severity. It also assessed whether these indices may have adjunctive value in distinguishing early-stage from late-stage osteoarthritis.

Methods

This retrospective study included 2176 patients diagnosed with knee osteoarthritis between January 1, 2023, and July 1, 2025. Patients aged 50–90 years with primary knee osteoarthritis and an available complete blood count (CBC) were included. Age, gender, Kellgren–Lawrence (KL) stage, neutrophil, lymphocyte, monocyte, and platelet counts were recorded. Neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), monocyte to lymphocyte ratio (MLR), systemic immune inflammation index (SII), systemic inflammation response index (SIRI), and pan-immune inflammation value (PIV) were calculated. Receiver operating characteristic (ROC) analysis and multivariable binary logistic regression adjusted for age and gender were performed.

Results

NLR (p < 0.001), MLR (p < 0.001), SII (p < 0.001), SIRI (p < 0.001), and PIV (p < 0.001) were significantly higher in patients with late-stage osteoarthritis, whereas PLR did not differ significantly between groups (p = 0.061). ROC analysis showed that NLR, MLR, SII, SIRI, and PIV had statistically significant but poor to modest discriminatory ability for late-stage osteoarthritis. Although SIRI showed the highest AUC among the evaluated indices, its performance remained within the modest range, and none of the markers demonstrated clinically meaningful discriminatory ability. In multivariable binary logistic regression analysis adjusted for age and gender, NLR, MLR, SII, SIRI, and PIV remained associated after adjustment for age and gender with late-stage osteoarthritis.

Conclusion

NLR, MLR, SII, SIRI, and PIV were associated with greater radiographic severity in knee osteoarthritis. Among the investigated biomarkers, SIRI, PIV, and SII showed relatively better discriminatory performance than the other indices; however, the overall ability of all markers to distinguish early-stage from late-stage osteoarthritis was limited. These findings suggest that CBC-derived inflammatory indices may serve as inexpensive adjunctive markers of radiographic severity, but they should not be used as stand-alone tools in clinical decision-making.