Delta Neutrophil Index as an Early Screening and Prognostic Marker for Revision after Non-traumatic Below-Knee Amputation: A Hospital-Based Study.

BACKGROUND

Below-knee amputation (BKA) is frequently performed but carries a meaningful risk of proximal re-amputation. Transcutaneous oxygen pressure (TcPO2) can aid prediction for re-amputation, yet its accuracy and availability are limited by patient and technical factors. Postoperative inflammatory testing also lacks standard guidelines and adds cost. The delta neutrophil index (DNI) is automatically derived from a routine complete blood count without additional testing or cost. In this study, we aimed to evaluate whether postoperative DNI predicts early conversion to above-knee amputation (AKA) after non-traumatic BKA.

METHODS

We retrospectively evaluated all BKA procedures performed in the Orthopedic Surgery Department at Wonju Severance Christian Hospital between 2011 and 2021. These procedures were identified using the Current Procedural Terminology code 27880. The characteristics of patients requiring AKA within 30 days after non-traumatic BKA (AKA group) were compared to those of patients who did not require further amputation (non-AKA group). The demographic characteristics, laboratory findings, and clinical outcomes of patients who underwent non-traumatic BKA were examined. Moreover, a multivariable logistic regression model and receiver operating characteristic (ROC) curve were developed to evaluate the prognostic value of the DNI for early AKA.

RESULTS

In total, 130 cases of non-traumatic BKA were identified. Proximal amputations within the first 30 postoperative days (PODs) were performed in 13 patients. Participants in the AKA group had significantly higher DNI on POD 1 compared with the non-AKA group (median [interquartile range], 2.3 [1.3-4.1] vs. 1.0 [0-2.3]; p = 0.022). In the multivariate analysis, the odds ratio for early AKA according to the DNI on POD 1 was 1.46 (95% CI, 1.03-2.08), and the area under the ROC curve of the DNI on POD 1 was 0.7 (with an optimal cutoff value of 1.95, a sensitivity of 0.73, and a specificity of 0.69).

CONCLUSIONS

In patients aged < 65 years undergoing BKA, POD 1 DNI-available from routine complete blood counts-can be used as a first-line screen and adjunctive prognostic marker to identify a higher risk of ipsilateral AKA within 30 days. Larger cohorts are needed to confirm thresholds and pathways.