Preoperative Systemic Immune-Inflammation Index, Neutrophil-to-Lymphocyte Ratio and Platelet-to-Lymphocyte Ratio for Predicting Postoperative Complications in Acute and Emergency Abdominal Surgery: A Systematic Review

Abstract

Background: Emergency laparotomy carries substantially higher morbidity and mortality than elective abdominal surgery, and established prognostic tools such as POSSUM, P-POSSUM and the National Emergency Laparotomy Audit (NELA) risk model, although well validated, require multiple physiological and intraoperative variables that are not always available at the time an operative decision must be made [1,2]. Ratios derived from the routine complete blood count — the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and systemic immune-inflammation index (SII, calculated as platelet count × neutrophil count / lymphocyte count) — have been proposed as inexpensive, immediately available adjuncts for perioperative risk stratification [3,4].
Objective: To synthesise the published evidence on the association between preoperative SII, NLR and PLR and postoperative complications and mortality in patients undergoing emergency general and abdominal surgery, and to relate these findings to established surgical risk-prediction tools.
Methods: A literature synthesis was undertaken with reference to the PRISMA 2020 framework [5]. Records were identified through structured searches of PubMed/MEDLINE, Scopus, Embase and Cochrane CENTRAL using combinations of inflammatory-marker terms (SII, NLR and PLR) and emergency/acute abdominal surgery terms. Eligible studies reported preoperative NLR, PLR and/or SII in adults undergoing emergency or acute-care general surgical procedures, with a postoperative complication, morbidity or mortality endpoint. Study quality was independently appraised by two reviewers using the Newcastle-Ottawa Scale (NOS) [6], with disagreements resolved by discussion and consensus. Because of heterogeneity in populations, outcome definitions, marker timing and cut-offs, findings were synthesised narratively rather than pooled in meta-analysis.
Results: Ten primary observational studies met the eligibility criteria for the qualitative synthesis, spanning emergency abdominal surgery, appendicectomy, acute-care surgery and emergency subgroups within abdominal surgical cohorts, with sample sizes ranging from 102 to 570 patients. Additional reviews and meta-analyses were used only for background and contextual comparison and were not treated as included primary studies. Reported discriminative performance for postoperative complications was inconsistent: area-under-the-curve (AUC) values for SII and NLR ranged from approximately 0.55 to 0.72 across studies, with several cohorts reporting significant independent associations after multivariable adjustment and at least one large cohort (n = 570) finding no independent association for NLR (AUC 0.55–0.60). Elevated preoperative NLR was more consistently associated with infective and septic complications than with the full spectrum of Clavien-Dindo ≥III morbidity. Evidence for SII specifically in emergency (as opposed to elective oncological) general surgery remains limited to a small number of cohorts.
Conclusion: SII, NLR and PLR are inexpensive, readily available markers that show a biologically plausible but inconsistent association with postoperative complications after emergency abdominal surgery. Current evidence does not support their use as stand-alone replacements for validated multivariable risk scores such as NELA or POSSUM; they may instead have value as low-cost adjuncts within composite risk models. Adequately powered, prospectively registered multicentre cohort studies with standardised outcome definitions and pre-specified cut-offs are needed before these indices can be recommended for routine perioperative risk stratification in emergency general surgery.