[Establishing reference ranges of serum vitamin K in healthy children].

<b>Objective:</b> To establish and validate reference intervals of serum vitamin K for healthy children in China. <b>Methods:</b> A cross-sectional study was conducted from January 2020 to May 2023, involving 807 healthy children aged 0 to 14 years, selected by stratified random sampling based on the population distribution of children in eastern, central, western, and northeastern China. Sample collection was carried out in 16 hospitals across 12 provinces, autonomous regions, and municipalities. Basic information of the children was collected using a standardized self-design questionnaire. Serum levels of vitamin K₁ and vitamin K₂ (menaquinone-4 (MK-4), menaquinone-7 (MK-7)) were measured using liquid chromatography-tandem mass spectrometry. The reference intervals was established by direct approach. The children were divided into different groups by age. Inter-group comparisons were conducted using the Kruskal-Wallis non-parametric test, and the reference intervals (<i>P</i>_2.5-<i>P</i>_97.5) were determined using non-parametric methods. Screening 40 healthy children for small sample validation based on age groups within the reference range(25 from eastern, 10 from central, and 5 from western regions). <b>Results:</b> The age of the 807 children was 5.00 (2.00, 9.81) years, and 495 (61.3%) were males and 312 (38.7%) females. Reference intervals were established for 795 children, of whom 303 children were aged 1 month to 3 years and 492 were aged 4 to 14 years. The reference intervals for serum vitamin K₁ were 0.09-4.54 μg/L for children aged 1 month to 3 years, and 0.10-1.73 μg/L for 4-14 years. For MK-7, the intervals were 0.07-1.42 μg/L for 1 month to 3 years and 0.19-2.03 μg/L for 4-14 years. The reference intervals for MK-4 in children aged 1 month to 14 years were 0-0.42 μg/L. The measured values of serum vitamin K₁, MK-4, and MK-7 in the validation samples did not exceed the reference limit in more than 2 samples. <b>Conclusion:</b> Reference intervals for vitamin K₁, MK-4, and MK-7 in healthy children aged 1 month to 14 years have been established and validated, and can be used to assess vitamin K nutritional status in children.