The Accuracy and Sensitivity of Delta Neutrophil Index in Malignancy: Diagnostic Study of Different Types

<b>Background/Objectives:</b> The delta neutrophil index (DNI)-a hematology analyzer-derived measure of circulating immature granulocytes-may assist pre-biopsy decision-making, yet its behavior across tumor types is incompletely defined. We examined whether pre-biopsy DNI differs by pathology category, tumor class, and definitive histology, and evaluated diagnostic performance. <b>Methods:</b> In this retrospective, single-center cohort, consecutive inpatients with malignancy were screened (<i>n</i> = 2009). Exclusions included positive blood cultures, prior chemotherapy/radiotherapy before index labs, and lack of definitive pathology, yielding 1313 analyzable cases. All laboratories, including DNI, were obtained before diagnostic biopsy. DNI was assessed as a continuous variable and categorized (Zero = 0; High > 0.6). Groupwise differences used Kruskal-Wallis and χ² tests with FDR control; discrimination used ROC analyses (one-versus-rest/pairwise). <b>Results:</b> DNI distributions differed across pathology, tumor class, and definitive diagnoses (all <i>p</i> < 0.001). High DNI (>0.6) and Zero DNI (=0) proportions also varied significantly by grouping. Hematologic malignancies showed the highest DNI (median ~1.0) compared with sarcoma and carcinoma (medians ~0.4). Using DNI alone, one-versus-rest AUCs were 0.735 (hematologic), 0.692 (melanoma), 0.672 (sarcoma), and 0.652 (carcinoma); the strongest pairwise separation was hematologic versus sarcoma (AUC 0.780). For specific solid tumors, including breast and renal cell carcinoma, single-marker discrimination was modest; no clinically actionable RCC cutoff emerged. Sensitivity analyses restricted to culture-negative cases yielded consistent findings. <b>Conclusions:</b> Pre-biopsy DNI exhibits tumor-type-dependent variation and provides adjunct diagnostic signal-the strongest for hematologic malignancy-yet is insufficient alone for solid tumor subtyping. Integration with clinical assessment and routine biomarkers, and multi-center validation with device harmonization are warranted.