Establishment of NT-proBNP reference intervals in a Malaysian population: a retrospective direct approach using a posteriori selection

Objectives To establish the first population-specific 95th percentile upper reference limit (URL) for N-terminal pro-B-type natriuretic peptide (NT-proBNP) in a health-associated Malaysian population using a retrospective direct approach with a posteriori selection. Methods Clinical laboratory data (n=3,113) from two university centres (January 2022–March 2025) were systematically screened following IFCC C-RIDL and CLSI EP28-A3c guidelines. Rigorous exclusion criteria; including a biochemical filter (>300 pg/mL), clinical history of cardiac or organ disease, interfering medications, and obesity (BMI ≥27.5 kg/m 2 ), were applied to isolate a healthy cohort. Following outlier removal via the Horn-Tukey method, the 95th percentile URL was determined nonparametrically with 1,000 bootstrap samples for a final reference population of n=121. Results The derived 95th percentile URL was 138.8 pg/mL (95 % CI: 112.8–151.0 pg/mL). Age was significantly associated with higher NT-proBNP levels (p=0.004), while sex (p=0.066), race (p=0.462), and BMI (p=0.138) showed non-significant variations with small-to-negligible effect sizes. Internal validation confirmed the stability of the threshold with a 2.9 % exceedance rate. Conclusions This study establishes a Malaysian-specific NT-proBNP baseline of 138.8 pg/mL. While overlapping with international 125.0 pg/mL benchmarks, this locally derived URL provides a necessary foundation for enhancing diagnostic specificity and optimizing healthcare resources in primary care heart failure screening within the Malaysian context.