Norifumi Kudeken
The prognostic nutritional index (PNI), calculated from serum albumin and lymphocyte count, is a simple immunonutritional marker originally proposed for surgical risk assessment. It has since been applied across multiple fields, but no comprehensive review has synthesized the evidence. This review aims to summarize current knowledge on PNI across oncology, cardiology, nephrology, infectious and respiratory diseases, geriatrics, and perioperative medicine. A narrative review was conducted using PubMed and Web of Science up to August 2025. Relevant studies and meta-analyses were identified, focusing on PNI as a predictor of mortality, complications, or treatment outcomes across specialties. Low PNI consistently predicts poor outcomes in cancer, including postoperative complications and reduced survival. In cardiology, PNI is linked to mortality in heart failure, acute myocardial infarction, and stroke. In nephrology, low PNI correlates with mortality in chronic kidney disease and dialysis patients. PNI also predicts severity and mortality in pneumonia and COVID-19, and is associated with frailty, delirium, and mortality in elderly populations. In perioperative care, PNI predicts complications and survival across surgical specialties. Comparisons with other indices (GNRI, CONUT, NRI) show context-dependent performance, with PNI remaining the most practical due to simplicity. PNI is a robust, low-cost, and widely applicable prognostic tool. However, limitations include variable cut-off values, susceptibility to acute-phase changes, and lack of interventional validation. Standardization and prospective trials are required before PNI can be fully integrated into clinical guidelines.