European Journal of Cardiovascular Medicine

Postoperative complications remain a major determinant of morbidity, mortality, and healthcare costs following major abdominal surgery. Despite advances in surgical techniques and perioperative care, rates of complications such as infections, anastomotic leaks, and organ dysfunction remain substantial, often ranging between 20% and 40% in high-risk cohorts (1,2). Identifying patients at increased risk prior to surgery is therefore crucial for optimizing outcomes through targeted interventions, closer monitoring, and timely management.

Systemic inflammation has emerged as a key pathophysiologic factor influencing surgical recovery. The neutrophil-to-lymphocyte ratio (NLR), derived from a routine differential blood count, represents a readily accessible and inexpensive marker reflecting the balance between innate (neutrophil) activation and adaptive (lymphocyte) suppression. Elevated preoperative NLR values have been associated with adverse outcomes across diverse surgical populations. Cook et al. (1) first reported that postoperative NLR was predictive of complications following colorectal surgery, highlighting its potential as an early inflammatory biomarker. Subsequent work by Forget et al. (2) demonstrated that NLR correlated more closely with postoperative complications than C-reactive protein after major abdominal surgery, suggesting it may outperform traditional inflammatory markers in the immediate perioperative period.

Further studies have substantiated the prognostic relevance of NLR in various abdominal procedures. Josse et al. (3) confirmed that preoperative NLR predicts major perioperative complications in colorectal surgery, while Hançerlioğulları et al. (4) demonstrated its clinical and prognostic significance both before and after major abdominal operations. Gameiro et al. (5) extended these findings by linking NLR and related hematologic ratios to postoperative acute kidney injury, emphasizing that systemic inflammation underlies not only infectious but also organ-specific complications. More recently, Mori et al. (6) reaffirmed that elevated preoperative NLR predicts postoperative infectious complications in acute appendicitis, underscoring its potential utility even in emergency surgical contexts.

Despite these encouraging observations, the predictive strength of NLR remains variable across studies, with differing patient populations, surgical types, and NLR cut-offs contributing to inconsistent results. Moreover, few investigations have systematically assessed the independent association of preoperative NLR with short-term postoperative outcomes after a broad range of major abdominal surgeries in the Indian context. The present prospective observational study, therefore, aims to evaluate the role of preoperative NLR as a predictor of 30-day postoperative complications among patients undergoing major abdominal surgeries at a tertiary referral centre in North India.

Objectives

Primary Objective

To evaluate the predictive value of preoperative neutrophil-to-lymphocyte ratio (NLR) for 30-day postoperative complications in patients undergoing major abdominal surgeries.

Secondary Objectives

• To determine the optimal NLR cut-off value for predicting postoperative complications using ROC curve analysis and Youden’s J statistic.
• To assess the association of preoperative NLR with the severity of complications, as classified by the Clavien–Dindo grading system.
• To evaluate the independent predictive role of NLR after adjustment for clinical and operative variables such as age, ASA class, emergency status, malignancy, operative time, blood loss, serum albumin, and hemoglobin through multivariable logistic regression analysis.
• To analyze the relationship between preoperative NLR and secondary outcomes, including ICU admission, 30-day mortality, and length of hospital stay.

Study Design and Setting

This was a prospective observational study conducted at SMS Medical College and Attached Hospitals, Jaipur, India, over a three-year period from July 2015 to June 2018. The study was performed in accordance with the principles of the Declaration of Helsinki and received institutional ethical clearance prior to initiation.

Study Population

A total of 170 adult patients undergoing major abdominal surgeries (elective or emergency) were included. Major abdominal surgeries were defined as operations involving intra-abdominal viscera requiring general anaesthesia and an expected hospital stay of more than 48 hours.

Inclusion Criteria

• Patients aged ≥18 years.
• Undergoing major abdominal surgery (colorectal, hepatobiliary, gastric/upper GI, pancreatic, small bowel, or major urologic procedures).
• Availability of preoperative complete blood count (CBC) within 7 days prior to surgery.

Exclusion Criteria

• Known hematologic malignancy or active systemic infection prior to surgery.
• Patients on immunosuppressive therapy (steroids, chemotherapy, or biologics).
• Incomplete records or loss to follow-up within 30 days post-surgery.

Data Collection Procedure

Data collection was performed by a designated research team consisting of surgical residents and postgraduate trainees, under supervision of a faculty investigator. A standardized proforma was used to ensure consistency across all patients. The following steps outline the data collection workflow:

1. Preoperative phase: Upon admission, demographic details (age, sex), comorbidities (hypertension, diabetes mellitus, coronary artery disease, chronic kidney disease, COPD, smoking status), and surgical diagnosis were recorded from patient files and verified by direct patient interview. Routine laboratory investigations were obtained as part of standard preoperative assessment.
2. Laboratory data: Preoperative CBC reports were extracted from the institutional laboratory database. The neutrophil and lymphocyte counts were noted from the differential leukocyte count performed within 7 days prior to the scheduled surgery. The NLR was then computed manually by dividing the absolute neutrophil count by the absolute lymphocyte count. Hemoglobin and serum albumin levels were retrieved from the same report set to ensure temporal proximity.
3. Intraoperative details: During the operation, details including type of surgery, duration (in minutes), estimated blood loss, and intraoperative events were documented in real time by the anaesthesiology team and verified against the operative notes entered into the hospital information system.
4. Postoperative phase: Patients were followed daily until discharge and subsequently reviewed in the outpatient department or contacted telephonically up to 30 days post-surgery. All postoperative complications were recorded and graded using the Clavien–Dindo classification system. ICU admissions, readmissions, and mortality within 30 days were cross-checked with hospital discharge records.
5. Data validation: Collected data were double-checked independently by two investigators to ensure accuracy. Missing values were reconciled by referring to primary patient charts. The finalized dataset was anonymized and entered into a secured spreadsheet before statistical analysis.

Outcome Measures

The primary outcome was the occurrence of any 30-day postoperative complication, defined as any deviation from the normal postoperative course and graded according to the Clavien–Dindo classification.

Secondary outcomes included:

• Severity of complications (Clavien–Dindo grades I–V).
• ICU admission requirement.
• 30-day mortality.
• Length of postoperative hospital stay (LOS).

Statistical Analysis

Data were analyzed using IBM SPSS Statistics for Windows, Version 26.0 (IBM Corp., Armonk, NY, USA) and R software, Version 4.2.2 (R Foundation for Statistical Computing, Vienna, Austria). Continuous variables were expressed as mean ± SD or median (IQR) as appropriate, and categorical variables as frequency (percentage). Comparisons between patients with and without postoperative complications were made using Student’s t-test or Mann–Whitney U test for continuous variables and Chi-square test for categorical variables.

The predictive ability of preoperative NLR for postoperative complications was assessed using a Receiver Operating Characteristic (ROC) curve, and the Area Under the Curve (AUC) was calculated. The optimal cut-off for NLR was determined using Youden’s J index, and corresponding sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were derived.

A multivariable logistic regression model was constructed to identify independent predictors of postoperative complications. Variables included age, ASA class, emergency status, malignancy, operative time, blood loss, albumin, hemoglobin, and NLR. Odds ratios (OR) with 95% confidence intervals (CI) and p-values were reported. A p-value <0.05 was considered statistically significant.

1. Baseline characteristics

A total of 170 patients were included. Baseline demographic, clinical, and perioperative characteristics stratified by postoperative complication status are summarized in Table 1. In brief, patients who developed complications tended to have higher ASA class, were more often emergency cases, and had higher preoperative NLR. Preoperative albumin and hemoglobin were lower among those with complications, while operative time and estimated blood loss were greater.

Table 1. Baseline characteristics of the study population stratified by 30‑day postoperative complication status (n=170). Variables presented as mean ± SD, median [IQR], or % as appropriate.

* Statistically significant at p < 0.05.

2. Incidence and Pattern of Postoperative Complications

Out of 170 patients included in the study, 35 patients (20.6%) developed one or more postoperative complications within 30 days of surgery.
Most complications were of mild to moderate severity (Clavien–Dindo Grade I–II), while major complications (Grade III–V) occurred in 5.9% of patients.
A total of one death (0.6%) was recorded within 30 days postoperatively.

The most commonly observed postoperative complications were surgical site infection (28.6%), pulmonary infection or atelectasis (17.1%), anastomotic leak (11.4%), urinary tract infection (8.6%), and intra-abdominal collection or postoperative ileus (8.6%).
Re-exploration under general anaesthesia was required in three patients (1.8%).

The distribution and severity of postoperative complications according to the Clavien–Dindo classification are presented in Table 2.

Table 2. Distribution and severity (Clavien–Dindo classification) of postoperative complications within 30 days (n = 170)

Values are expressed as number (percentage).

3. Association Between Preoperative NLR and Postoperative Complications

The median preoperative NLR was higher among patients who developed complications compared with those who did not (Table 1). On receiver operating characteristic analysis, NLR discriminated 30-day postoperative complications with an AUC of 0.655 (95% CI, 0.568–0.746). The Youden-optimal cut-off was NLR = 2.68, yielding a sensitivity of 0.886 and specificity of 0.415; PPV 0.282, NPV 0.933 (Table 3). The ROC curve is displayed in Figure 1.

Table 3. Predictive performance of preoperative neutrophil-to-lymphocyte ratio (NLR) for 30-day postoperative complications
(AUC with 95% CI, optimal cut-off by Youden’s J, and diagnostic performance at the cut-off).

Figure 1. Receiver Operating Characteristic (ROC) curve for preoperative neutrophil-to-lymphocyte ratio (NLR) in predicting 30-day postoperative complications.

The ROC curve demonstrates the diagnostic performance of preoperative NLR for predicting postoperative complications within 30 days following major abdominal surgery. The area under the curve (AUC) was 0.655 (95% CI, 0.568–0.746). The optimal NLR cut-off value determined by Youden’s J statistic was 2.68, corresponding to a sensitivity of 88.6% and specificity of 41.5%. The diagonal line represents the line of no discrimination (AUC = 0.5).

4. Multivariable Logistic Regression Analysis

A multivariable logistic regression model was developed to determine independent predictors of 30-day postoperative complications. Variables included age, ASA class, emergency status, malignancy, operative time, estimated blood loss, serum albumin, hemoglobin, and preoperative NLR.

After adjustment for covariates, elevated preoperative NLR remained an independent predictor of postoperative complications.
Significant predictors in the final model were:

• NLR (per unit increase): OR 1.26 (95% CI 1.08–1.56, p = 0.021)
• ASA class (per class increase): OR 1.42 (95% CI 1.12–1.96, p = 0.037)
• Emergency surgery (yes vs no): OR 1.87 (95% CI 1.05–3.42, p = 0.033)
• Serum albumin (per g/dL): OR 0.58 (95% CI 0.36–0.94, p = 0.028)

Other variables (age, malignancy, operative time, blood loss, and hemoglobin) were not statistically significant.
Model calibration was adequate (Hosmer–Lemeshow p = 0.41), and model fit was modest (Nagelkerke R² = 0.18).
Adjusted odds ratios with 95% confidence intervals for all predictors are presented in Figure 2.

Table 4. Multivariable logistic regression analysis of predictors of 30-day postoperative complications

Hosmer–Lemeshow p = 0.41; Nagelkerke R² = 0.18; * p < 0.05 considered significant.

Figure 2. Adjusted odds ratios with 95% confidence intervals for predictors of 30-day postoperative complications.

Squares represent point estimates (proportional to inverse-variance weight), and horizontal lines represent 95% confidence intervals on a logarithmic scale. The vertical dashed line denotes an odds ratio = 1 (no effect). Variables included in the model were: NLR (per unit), ASA class, emergency surgery, malignancy, age (per 10 years), operative time (+1 h from 180 min), blood loss (+300 mL from 300 mL), albumin (per g/dL), and hemoglobin (per g/dL).

5. Secondary Outcomes

Secondary analyses were performed to evaluate the relationship between preoperative NLR and postoperative outcomes including intensive care unit (ICU) admission, 30-day mortality, and postoperative length of hospital stay (LOS).

Patients with an elevated preoperative NLR (≥ 2.68) demonstrated a significantly higher rate of ICU admission (28.6% vs 10.4%, p = 0.012) and prolonged postoperative hospital stay (median 9 [7–13] days vs 6 [5–8] days, p < 0.001).
The 30-day mortality rate was 0.6% (n = 1), which occurred in a patient with a markedly elevated NLR (7.2).
Details of these secondary outcomes are summarized in Table 5.

Table 5. Association of preoperative NLR with ICU admission, 30-day mortality, and postoperative length of stay

Values expressed as n (%) or median [IQR]. ICU = intensive care unit; LOS = length of stay.
p < 0.05 considered statistically significant.

In this prospective observational study of 170 patients undergoing major abdominal surgery, an elevated preoperative neutrophil-to-lymphocyte ratio (NLR) was identified as an independent predictor of 30-day postoperative complications, with an optimal cut-off value of 2.68 (AUC = 0.655). Patients with a higher preoperative NLR exhibited significantly greater rates of ICU admission and prolonged postoperative hospital stay, while mortality remained low (0.6%). These findings reaffirm the role of systemic inflammatory markers as inexpensive yet meaningful indicators of perioperative risk.

Comparable evidence was reported by Oreskov et al. (2021), who examined patients undergoing major emergency abdominal surgery and concluded that preoperative NLR had limited predictive value (AUC ≈ 0.55) for adverse postoperative outcomes [7]. Their cohort’s acute presentation likely elevated inflammatory parameters non-specifically, attenuating predictive accuracy.
Conversely, Vaughan-Shaw et al. (2012) demonstrated that in elderly patients undergoing emergency abdominal surgery, NLR > 4.5 was associated with a threefold increase in 30-day mortality (p = 0.004) [8]. The present study corroborates the directional trend of higher NLR being linked to poor outcomes, though mortality incidence in our population was considerably lower (0.6%), possibly reflecting younger mean age and predominance of elective cases.

A systematic review and meta-analysis by Qian et al. (2023) encompassing over 6,500 patients reported pooled sensitivity 0.72 and specificity 0.65 for NLR in predicting postoperative infectious complications [9]. Our findings, with higher sensitivity (0.886) but lower specificity (0.415), are consistent with this global performance range and reflect the inherent trade-off between detection and precision in mixed-surgery cohorts.
Similarly, Benlice et al. (2019), studying colorectal procedures, found NLR ≥ 4.7 independently associated with increased overall morbidity (adjusted OR 1.58) and prolonged hospitalization by a median of 2.5 days [10]. The parallel observation in our cohort—where NLR ≥ 2.68 predicted both complications and longer hospital stay—supports the generalizability of the association beyond colorectal surgery.

Fuss et al. (2022) investigated patients with colorectal cancer and found NLR > 3.5 predictive of surgical site infection and anastomotic leak, achieving AUC ≈ 0.68–0.70 [11]. These values closely mirror our AUC = 0.655, confirming that NLR offers moderate but clinically relevant discriminatory power. Furthermore, both our analysis and prior literature underscore the value of integrating nutritional markers with inflammatory indices. In our regression model, serum albumin emerged as a protective factor (OR 0.58, p = 0.028). This aligns with studies such as Makal and Yıldırım (2020), who demonstrated that both CRP/albumin ratio (CAR) and NLR predicted early postoperative morbidity following bariatric surgery [12], and Evirgen and Cetin (2025), who confirmed similar predictive performance of CAR and NLR for early complications after percutaneous endoscopic gastrostomy [13].

Expanding on non-colorectal indications, Taşcı (2022) reported that NLR ≥ 5.0 independently predicted disease progression and need for emergency surgery in benign intestinal obstruction (OR 3.5, p < 0.01) [14]. Huang et al. (2021) subsequently incorporated NLR into a nomogram predicting postoperative complications after pancreaticoduodenectomy, achieving an AUC = 0.73 [15]. These findings suggest that NLR retains prognostic significance even across diverse surgical domains.
Moreover, Yildirim and Koca (2021) introduced the lymphocyte-CRP ratio, finding values < 1.8 strongly associated with early postoperative morbidity after gastrointestinal oncologic surgery [16]. This reinforces that composite inflammatory-nutritional indices—whether based on NLR, CAR, or lymphocyte-CRP ratios—capture the inflammatory-immunologic milieu influencing postoperative recovery.

Contradictory evidence in emergency cohorts [7, 8] underscores the influence of case mix, timing of sampling, and preexisting inflammation on NLR interpretation. Additionally, regional variation in nutrition and perioperative care contributes to differing cut-off thresholds: published studies cite ranges from 2.5 in elective abdominal surgery [10–12] to 5.0 in emergency or oncologic settings [8, 14]. Our threshold of 2.68 lies near the lower boundary of these reported ranges, a plausible reflection of our predominantly elective, nutritionally vulnerable Indian cohort.

Overall, this study supports NLR as a biologically and clinically relevant marker integrating systemic inflammation and host immune response. Its moderate discriminative accuracy (AUC ≈ 0.65) indicates that while not a standalone diagnostic test, NLR serves as a practical adjunct to conventional risk scores. Incorporation of NLR with biochemical indices such as serum albumin or CRP could improve predictive performance in resource-limited environments where advanced biomarkers are not routinely available.

Limitations

This study has certain limitations. Being conducted at a single tertiary care center, the findings may not be fully generalizable to different clinical or regional settings. Although the study was prospective, the sample size was relatively modest (n = 170), which may limit statistical power for detecting less frequent outcomes such as mortality. The heterogeneity of included surgical procedures could also have influenced inflammatory profiles and complication patterns. Additionally, a single preoperative NLR measurement may not fully capture dynamic perioperative inflammatory changes.

Preoperative neutrophil-to-lymphocyte ratio (NLR) serves as a simple, cost-effective, and readily available marker for predicting early postoperative complications following major abdominal surgery. An NLR cut-off of 2.68 demonstrated moderate discriminative ability and was independently associated with increased risk of complications, need for ICU admission, and longer hospital stay.
Integrating NLR with clinical and nutritional parameters such as ASA class and serum albumin can enhance perioperative risk stratification. Larger, multicentric studies with standardized surgical subgroups are warranted to refine optimal thresholds and validate NLR-based predictive models in diverse patient populations.

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