Systemic inflammatory indices SIRI, AISI, and PWR are associated with sarcopenic obesity in middle-aged and older chinese adults: a cross-sectional study

Chronic low-grade inflammation is implicated in sarcopenic obesity (SO); however, the relevance of routinely available blood cell inflammatory indices in SO remains unclear. This study aimed to examine the association between these indices and SO. This cross-sectional study included 1,009 participants aged ≥ 50 years. SO was defined by the presence of both sarcopenia (defined based on sex-specific muscle mass percentage cutoffs: muscle mass < 39.3% for men or < 33.9% for women) and obesity defined as body mass index (BMI) ≥ 28 kg/m², body fat percentage (PBF) ≥ 30% for men or ≥ 40% for women, visceral fat area (VFA) ≥ 100 cm², or waist circumference (WC) ≥ 80 cm for women and ≥ 90 cm for men. Inflammatory indices, including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), platelet-to-white blood cell ratio (PWR), systemic immune-inflammatory index (SII), systemic inflammation response index (SIRI), and aggregate inflammation systemic index (AISI), were calculated from routine blood tests. Multivariable logistic regression models were used to examine the associations between these indices and SO, with adjustments for potential confounders. When the WC classification was used, risk of SO was significantly associated with SIRI (OR = 1.361, 95% CI: 1.057–1.753; P = 0.017) and AISI (OR = 1.248, 95% CI: 1.022–1.524; P = 0.029), but inversely associated with PWR (OR = 0.621, 95% CI: 0.390–0.988; P = 0.040). Similar modest associations were observed under the VFA classification. Under the BMI ≥ 28 kg/m² definition, SIRI (OR = 1.539, 95% CI: 1.133–2.092; P = 0.006) and AISI (OR = 1.374, 95% CI: 1.066–1.771; P = 0.014) remained significantly associated with SO, with effect sizes in the modest-to-moderate range. However, no significant associations were observed when SO was defined using PBF, suggesting that inflammatory indices may be more closely related to central rather than generalized adiposity. The association between systemic immune inflammation indices and SO varied according to the obesity classification method. Given the cross-sectional design, these findings reflect associations rather than causality. SIRI, AISI, and PWR may have potential value in risk stratification, particularly under WC, VFA, or BMI ≥ 28 kg/m² definitions. Prospective studies with external validation are needed to confirm their clinical utility.