VALIDATION OF THE LC-MS/MS METHOD FOR 25-HYDROXYVITAMIN D DETERMINATION IN CHILDREN'S SERUM ACCORDING TO VDSP STANDARDS

AIM. To verify the LC-MS/MS method for 25-hydroxyvitamin D (25(OH)D) determination in children’s serum according to VDSP requirements, evaluate its analytical performance, and compare it with ECLIA to substantiate its use in hygienic monitoring of pediatric vitamin D status. MATERIALS AND METHODS. The study was based on a retrospective laboratory database (>70,000 analyses, 2022–2025) and a prospective representative sample of children aged 3–17 years (n=562; 289 boys, 273 girls) from Southern Ukraine (2023–2025). LC-MS/MS verification was performed using four levels of NIST SRM 972a according to VDSP criteria. Comparison with ECLIA (Roche Cobas) was carried out in a subsample (n=120) using Pearson correlation, Passing-Bablok regression, Bland-Altman analysis, and ICC. RESULTS. The LC-MS/MS method demonstrated high precision (total CV≤7.3%) and trueness (bias from –2.0% to –0.8%), fully meeting VDSP requirements. Participation in DEQAS confirmed result stability during 2022–2025. Comparison with ECLIA showed strong correlation (r=0.97; p<0.001) but systematic overestimation by the immunoassay (+6.5 nmol/L; 95% LoA: –6.4 to +19.4 nmol/L). In the pediatric sample, 25(OH)D insufficiency (<50 nmol/L) was found in 71.9% and deficiency (<30 nmol/L) in 25.3% of children, with a significant age-related decline (p<0.001). CONCLUSIONS. The LC-MS/MS method was verified according to VDSP/DEQAS standards and is recommended as the reference method for hygienic monitoring of vitamin D status in Ukrainian children. ECLIA systematically overestimates 25(OH)D levels, requiring adjustment in clinical practice.