Stress index (glucose-to-potassium ratio) as a predictor of outcome in traumatic brain injury: systematic review and meta-analysis

Background Traumatic brain injury (TBI) is a major cause of death and disability. The glucose-to-potassium ratio (GPR), or stress index (SI), reflects stress hyperglycemia and hypokalemia and may improve early prognostication beyond clinical and radiologic scores. Methods We performed a PRISMA-guided systematic review and meta-analysis of observational cohort studies in adults (≥18 years) with CT-confirmed TBI reporting admission glucose and potassium and their association with mortality or functional/“poor outcome.” Random-effects models pooled odds ratios (ORs) for dichotomous outcomes and mean differences (MDs) for continuous GPR values; heterogeneity was assessed with I 2 . Prespecified subgroup analyses were conducted by sample size (>500 vs. < 500), with sensitivity analyses (leave-one-out; fixed vs. random) and funnel-plot inspection to explore robustness and small-study effects. Results Three studies (4,550 patients) contributed to the primary comparison of high versus low GPR and mortality. High GPR was associated with increased odds of death (pooled OR 11.97, 95% CI 2.68–53.37; p = 0.001; I 2 = 88%). Across four studies, patients with poor outcomes had higher admission GPR than those with good outcomes (pooled MD 16.82, 95% CI 12.70–20.94; p < 0.00001; I 2 = 61%). In five studies evaluating GPR as a prognostic predictor, the pooled adjusted OR for adverse outcome was 2.10 (95% CI 1.51–2.93; p < 0.0001; I 2 = 37%). Effects were larger in small single-center cohorts and more moderate, but significant, in the large registry-based study; sample size explained much of the between-study heterogeneity. Funnel-plot asymmetry suggested possible small-study effects/publication bias. Conclusion Elevated admission GPR/SI is associated with increased mortality and poor outcome in adult TBI and may capture early systemic stress. As a bedside metric derived from routine laboratory tests, it is a promising adjunct for early risk stratification. However, heterogeneity, small-study effects, and observational evidence warrant cautious interpretation; large multicenter prospective studies are needed to validate standardized thresholds and incremental value over existing prognostic models.