Characterization and traceability of two generations of standard reference material for the measurement of vitamin K1(phylloquinone) at endogenous concentrations in human plasma and serum

Vitamin K is an essential micronutrient required for blood coagulation, regulation of vascular calcification and bone mineralization. Plasma and serum measurements of vitamin K₁(phylloquinone, K₁) made using high-performance liquid chromatography with fluorescence detection, or tandem mass spectrometry are used clinically and in population studies to assess vitamin K status. Standard reference materials provide a validation tool for laboratories, helping assure clinical diagnosis and the comparability of data from different populations. We manufactured two K₁ standard reference materials, in 2009 (KEQAS SRM-001) and in 2019 (KEQAS SRM-002). The target concentrations of K₁ were assigned to each SRM using the All Laboratory Trimmed Mean of results reported by selected laboratories enrolled in the Vitamin K External Quality Assurance Scheme (KEQAS). The assigned concentrations of K₁ for KEQAS SRM-001 and SRM-002 were 0.25 and 0.36 μg/L respectively. In 2019 KEQAS SRM-001 was re-analysed simultaneously with KEQAS SRM-002 to provide traceability between the two standards, therefore aiding comparability of analysis performed using these materials. Both standards were stored as aliquots at −80°C in the dark; annual re-analysis of the materials indicated that K₁ is stable for at least 12 years in these conditions.