Establishment and validation of reference intervals for the neutrophil CD64 index in a healthy adult population from Guangxi, China.

BACKGROUND: The neutrophil CD64 (nCD64) index is a potent biomarker for infectious diseases; however, the lack of standardized reference intervals (RIs) limits its clinical utility. OBJECTIVES: This study aimed to establish and validate reference intervals (RIs) for the nCD64 index specifically for the Guangxi population using flow cytometry. DESIGN: Cross-sectional study. SETTINGS: Conducted in Guangxi, China. PATIENTS AND METHODS: A total of 494 healthy adults (aged 18-83 years) were enrolled. Peripheral blood nCD64 expression was measured via flow cytometry. Reference intervals were determined using the non-parametric 95th percentile method (2.5th-97.5th) per CLSI EP28-A3c guidelines. Validation was performed in an independent cohort (n=30). MAIN OUTCOME MEASURES: The primary outcome was the 95% reference interval for the nCD64 index. Secondary outcomes included correlations between nCD64 index and sex, age, BMI, and primary hematological parameters. SAMPLE SIZE: 494 healthy adults for establishment, plus 30 independent subjects for validation. RESULTS: ) indicated no requirement for sex-specific partitioning. No significant correlations were observed between nCD64 and age, BMI, or primary hematological parameters. The established 95% RI was .08-0.94, with the 90% confidence intervals (CI) for the lower and upper limits were .08-.09 and .92-1.04. Validation confirmed the RI's reliability, with 97% (29/30) of results falling within the range. CONCLUSIONS: We established a robust RI (.08-.94) for the nCD64 index in the Guangxi population, which remained consistent across age and sex groups. This provides a standardized baseline for the diagnosis of inflammatory and infectious conditions in Southern China. LIMITATIONS: The study was limited to a single regional population (Guangxi) and did not include pediatric or pregnant populations. Additionally, potential confounding from subclinical inflammation or undiagnosed chronic infections cannot be completely excluded despite strict enrollment criteria.