Abstract
PURPOSE: Hypertension is a major global health problem and one of the most common chronic conditions managed in primary care. Increasing evidence indicates that chronic low-grade inflammation plays a key role in the development of hypertension. The systemic immune-inflammation index (SII), calculated from routine complete blood count parameters, reflects the balance between immune and inflammatory activity. This study aimed to investigate the association between systemic immune-inflammation index and hypertension and to evaluate its potential value as a screening and risk stratification biomarker in primary care. METHODS: This retrospective case–control study included 655 hypertensive patients and 669 healthy controls aged ≥ 18 years. Individuals with acute or chronic infections, malignancy, autoimmune, or rheumatologic diseases were excluded. SII was calculated using the formula platelet × neutrophil / lymphocyte. Statistical analyses were performed using the Mann–Whitney U test, multivariate logistic regression, and receiver operating characteristic (ROC) curve analysis. RESULTS: A total of 1.324 participants were analyzed. Median SII values were significantly higher in hypertensive patients compared with healthy controls (536.9 vs. 381.3, p < 0.0001). ROC analysis identified an optimal SII cut-off value of 520.45 for predicting hypertension (AUC = 0.73; 95% CI: 0.70–0.76), with 52.4% sensitivity and 83.6% specificity. Individuals with an SII value above 520.45 had a significantly higher likelihood of having hypertension. When the reference group was defined as SII ≤ 520.45, the odds of hypertension were 7.3-fold higher in individuals with SII > 520.45 (OR = 0.137, B = − 1.986, 95% CI: 0.099–0.191; p < 0.0001). Notably, SII levels were significantly higher in newly diagnosed hypertensive patients compared with those previously diagnosed (p < 0.001), suggesting a stronger inflammatory response at early disease stages. No significant difference in SII values was observed between the “Hypertension only” and “Hypertension with comorbidity” groups (p = 0.596), suggesting that elevated SII levels may be primarily associated with hypertension itself rather than the presence of additional comorbidities. CONCLUSIONS: SII levels are significantly elevated in patients with hypertension. Although its low sensitivity limits its use as a standalone screening tool, SII may serve as a specific and easily accessible adjunctive marker for risk stratification in primary care settings.