Systemic immune-inflammation index: a novel tool for hypertension management in primary care

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. 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. 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. 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.