Diagnostic accuracy of NLR, MLR, PLR, SII, and SIRI for predicting major adverse maternal outcomes in preeclampsia: A systematic review.

ObjectivePreeclampsia is a major contributor to maternal morbidity worldwide, and early identification of women at risk of major adverse maternal outcomes is essential. However, commonly used biomarkers are costly and poorly accessible. Complete blood count-derived inflammatory ratios are inexpensive and widely available, but their prognostic value remains unclear. Therefore, this study aimed to evaluate whether complete blood count-derived inflammatory ratios are associated with major adverse maternal outcomes (a diagnostic-prognostic question) and whether they can differentiate women with preeclampsia.MethodsWe conducted a Preferred Reporting Items for Systematic reviews and Meta-Analyses 2020-compliant systematic review of observational studies, prospectively registered in International Prospective Register of Systematic Reviews (CRD420251275277). We conducted an extensive search across Scopus, PubMed, Web of Science, and Lens.org for studies published between January 2015 and December 2025. Eligible studies enrolled women with preeclampsia and assessed at least one complete blood count-derived inflammatory ratio (neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, systemic immune-inflammation index, systemic inflammation response index, or delta neutrophil index ) in association with at least one major adverse maternal outcome. Risk of bias was assessed using Quality Assessment of Diagnostic Accuracy Studies-2 and certainty of evidence using Grading of Recommendations Assessment, Development and Evaluation. Owing to substantial heterogeneity in designs, ratios, cutoffs, timing, and outcomes, no meta-analysis was performed, and findings were synthesized narratively.ResultsFifteen studies comprising 11,224 participants were included, of whom 5950 were women with preeclampsia and 1700 were normotensive controls. The remaining participants formed other comparison groups within large screening or hospital cohorts. Neutrophil-to-lymphocyte ratio was the most consistently evaluated marker and demonstrated good-to-excellent discrimination for severe disease and multiorgan complications (area under the curve range: 0.70-0.99). An elevated neutrophil-to-lymphocyte ratio was associated with hemolysis elevated liver enzymes low platelets syndrome, eclampsia, acute kidney injury, and intensive care unit admission. Platelet-to-lymphocyte ratio showed inconsistent patterns, with lower values particularly reported in women with hemolysis elevated liver enzymes low platelets syndrome. Evidence for systemic immune-inflammation index and systemic inflammation response index was limited, and substantial heterogeneity in cut-off values was observed.ConclusionsComplete blood count-derived inflammatory ratios, particularly neutrophil-to-lymphocyte ratio, demonstrated potential as low-cost adjunctive markers of risk in women with preeclampsia. However, the evidence is limited by heterogeneity, predominantly retrospective designs, severity-only and composite outcomes, and sparse outcome-specific data. These ratios should not currently be used as standalone clinical decision tools, and prospective validation in high-burden settings is required before implementation.