Objective To investigate the correlation between systemic immune inflammation index (SII) and carotid plaque in middle-aged patients with essential hypertension (EH).

Methods  A total of 4 782 middle-aged patients with EH who received carotid ultrasound examination at the Health Management Center of the First Affiliated Hospital of Anhui Medical University between January and December 2023 were selected and divided into the non-plaque group (n=3 570) and the plaque group (n=1 212) according to the results of carotid ultrasound. The general clinical and laboratory information was collated and subsequently compared between the two groups. Furthermore, the plaque detection rate and plaque characteristics (including plaque acoustic characteristics and the number and sites of occurrence) were analysed according to the SII tertile groups. Multivariate logistic regressions were used to analyse the impact of SII on carotid plaque in middle-aged patients with EH. Subgroup analyses were conducted with interaction effects investigating.

Results  The SII level in the plaque group was significantly higher than that in the non-plaque group (459.99±164.19 vs 389.47±140.99, t=−13.372, P＜0.001). The SII level was significantly higher in patients with homogeneous hypoechoic or inhomogeneous echo plaques than in patients with homogeneous strong echo or isoechoic plaques (495.64±169.61 vs 428.43±152.57, t=−7.262, P＜0.001). Furthermore, the SII level was significantly elevated in cases of bilateral or multiple plaques compared to cases of unilateral single ones (500.24±189.13 vs 425.18±129.50, t=−7.936, P＜0.001). The SII tertile grouping analysis demonstrated a gradual increase in the carotid plaque detection rate from the low to high tertile group (16.8% vs 23.7% vs 35.5%, χ²=152.043, P＜0.001). Among patients with plaques, the proportion of homogeneous strong or isoechoic plaques exhibited a gradual decline from the first to the third tertile group of SII (70.4%, 52.9%, and 45.0%, respectively), while the proportion of homogeneous hypoechoic or inhomogeneous plaques exhibited a gradual increase (29.6%, 47.1%, and 55.0%, respectively), and the difference was statistically significant (χ²=47.166, P＜0.001). In addition, the proportion of unilateral single plaques gradually decreased (62.9%, 59.8%, and 45.1%, respectively), while the proportion of bilateral or multiple plaques gradually increased (37.1%, 40.2%, and 54.9%,respectively), with a statistically significant difference (χ²=31.430, P＜0.001). After adjusting for confounding variables, multivariate logistic regression analyses demonstrated that for every one standard deviation (150.36) increase in the SII, the odds ratio (95% confidence interval) OR (95%CI) for the presence of carotid plaques was 1.533 (1.428–1.645). In comparison to the first tertile of SII, the risk of carotid plaque presence significantly increased in the second and third tertiles (P for trend＜0.001),with ORs (95%CI) of 1.361 (1.131–1.638) and 2.538 (2.122–3.035), respectively. Further subgroup analyses revealed that the significant association between SII and carotid plaques remained consistent across multiple subgroups, and interaction tests did not yield meaningful results (all P＞0.05).

Conclusion  Elevated SII level is an influencing factor for carotid plaque in middle-aged patients with EH, and is correlated with the number and stability of plaque.