Introduction: We assessed whether postoperative day-1 (POD-1) complete blood count (CBC) test parameters, including red cell distribution width (RDW), mean platelet volume (MPV), plateletcrit (PCT), platelet-to-lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR), could identify patients with gastric leaks after laparoscopic sleeve gastrectomy (LSG)., Methods: Patients with postoperative gastric leaks (n=36) and patients with no complications who were selected by age-sex-BMI matching (n=254) were included in the study. The levels of RDW, MPW, PCT, PLR, and NLR were compared between groups in univariate analyses. Receiver operating characteristic (ROC) curve analysis was run for CBC parameters with a P-value<0.05 in univariate analyses. The area under the curve (AUC) was evaluated, and a cutoff value was determined. Sensitivity, specificity, likelihood ratio (LR), positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated., Results: The level of PCT was significantly lower, while levels of PLR and NLR were significantly higher in patients with postoperative gastric leaks as compared with those without (P<0.05). The AUC of both PCT and PLR was <0.750, while the AUC of NLR was 0.911. NLR cutoff at 3.6 yielded 80% sensitivity, 92% specificity, and an LR of 10. In the study cohort, PPV of 59%, NPV of 97%, and an accuracy of 90% were found., Conclusions: Our results suggest that NLR at POD-1, with a cutoff value of 3.6, is a useful indicator of postoperative gastric leak who underwent LSG. We recommend the use of this easily calculated parameter in clinical practice., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)