Higher SII was associated with a greater ascending aortic diameter and with the presence of AAD after adjustment for the measured covariates, but the adjusted difference was modest, discrimination was weak, body size could not be accounted for, and the findings do not support SII as a standalone diagnostic marker for ascending aortic dilatation.
Key Findings
Results
In unadjusted comparisons, several blood markers and all five inflammatory indices were higher in patients with ascending aortic dilatation (≥40 mm) than in those without, while C-reactive protein did not differ.
251 adults who underwent thoracic CT angiography were grouped by maximum tubular ascending aortic diameter: <40 mm (n = 158) and ≥40 mm (n = 93).
Platelet and neutrophil counts, creatinine and all five inflammatory indices were nominally higher in the dilated group (all p < 0.05).
C-reactive protein did not differ between groups.
Results
In the primary adjusted linear model, higher SII was associated with greater ascending aortic diameter.
Each 100-unit increase in SII was associated with a 0.59 mm greater diameter (HC3 95% CI 0.28 to 0.90; β = 0.197; p < 0.001).
This corresponds to approximately 1.6 mm across the interquartile range of SII.
The model explained 26.9% of the variance.
Inference used heteroscedasticity-consistent (HC3) standard errors.
Results
Higher SII was associated with higher odds of ascending aortic dilatation in the secondary logistic model.
Odds ratio per 100 units of SII was 1.34 (95% CI 1.17 to 1.53; p < 0.001).
AAD was defined by a 40 mm threshold of maximum tubular ascending aortic diameter.
Results
SII showed weak discrimination for ascending aortic dilatation.
Area under the curve for SII was 0.658 (95% CI 0.590 to 0.726).
The sample-derived cut-off gave a positive likelihood ratio of 1.38.
The 2.5–97.5th percentile interval for the cut-off on bootstrap internal validation was 305 to 579, indicating an unstable cut-off.
Results
The exploratory correlation analyses did not survive multiple-testing correction, and there was no evidence of effect modification by sex.
None of the 75 correlations survived false discovery rate adjustment.
The SII-by-sex interaction was not significant (p = 0.621).
Methods
The study has important limitations, notably the absence of body size data, so residual confounding cannot be excluded.
Height and weight were not recorded, so models could not be adjusted for body size.
Design was single-centre, retrospective and cross-sectional, with 251 patients (mean age 53.1 ± 16.7 years; 160 men).
Cross-sectional design precludes conclusions about causality or temporal direction.
Conclusions
The authors conclude that SII is associated with aortic size but does not support use as a standalone diagnostic marker.
The adjusted difference in diameter was described as modest and discrimination as weak.
Association was observed after adjustment for the measured covariates only.
What This Means
This study looked at whether a simple number calculated from routine blood tests, called the systemic immune-inflammation index (SII), relates to the size of the ascending aorta (the first part of the body's main artery, leaving the heart). The researchers reviewed records of 251 adults who had a chest CT angiography scan, and compared those whose ascending aorta measured 40 mm or more (dilated) with those below 40 mm.
The research suggests that higher SII was linked to a somewhat wider ascending aorta. Each 100-unit increase in SII went with about 0.59 mm larger diameter after accounting for other measured factors, and also with higher odds of having a dilated aorta. However, SII was not good at telling patients with and without dilatation apart (AUC 0.658), and the cut-off value it suggested was unstable when tested by resampling. Other correlations explored in the study did not hold up after statistical correction for multiple testing.
Importantly, height and weight were not available, so body size, which strongly affects aortic size, could not be accounted for. The study also looked at one centre at one point in time, so it cannot show that inflammation causes aortic widening. The authors conclude these results do not support using SII on its own as a test for ascending aortic dilatation.
Yılmaz S, Nahir M, Çelik A. (2026). Association of the Systemic Immune-Inflammation Index with Ascending Aortic Diameter and Dilatation: A Retrospective Cross-Sectional Study.. Medicina (Kaunas, Lithuania). https://doi.org/10.3390/medicina62101892