Background Both albumin and phosphate are important biomarkers, with albumin reflecting nutritional status and inflammation, while phosphate plays a vital role in cellular metabolism and signaling. The phosphate-to-albumin ratio (PAR) integrates these two parameters, potentially serving as a composite marker linking nutritional and metabolic dysfunction in sepsis. This study examines the association between PAR and 28-day mortality in Vietnamese septic patients. Methods A retrospective observational study was conducted on patients with sepsis or septic shock admitted to the intensive care unit of a tertiary hospital in Vietnam. Serum phosphate and albumin level were collected within the first 24 h of diagnosis to calculate PAR. The primary outcome was 28-day mortality. Results A total of 333 septic patients were evaluated, with a mean age of 67.7 ± 17.6 years, and 62.8 % were male. The median PAR was significantly higher in non-survivors compared to survivors (5.42 vs. 3.85, p < 0.001). The area under the receiver operating characteristic curve (AUC) for PAR in predicting mortality was 0.66 (95 % CI: 0.60–0.72, p < 0.001). In multivariate logistic regression analysis, PAR remained an independent predictor of 28-day mortality (OR: 1.114, 95 % CI: 1.021–1.215, p = 0.015). Conclusion The phosphate-to-albumin ratio is an accessible, novel biomarker that reflects both nutritional and metabolic disturbances in septic patients and independently predicts 28-day mortality. Further research is needed to validate this finding.
