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CCQM K132 Low-Polarity Analytes in a Biological Matrix: Vitamin D Metabolites in Human Serum



Stephen Wise, Susan Tai, David L. Duewer


Vitamin D is a fat-soluble vitamin that occurs primarily in two forms, vitamin D2 and vitamin D3. Vitamin D3 is produced naturally when skin is exposed to UV radiation, is naturally-occurring in foods (generally of animal origin), and is fortified in some foods and dietary supplements. Vitamin D2 occurs in food (generally plant sources) and until recently was the form most often used in dietary supplements. Vitamin D is metabolized in the body to produce several closely related, hydroxylated species (metabolites), with 25-hydroxyvitamin D3 [25(OH)D3] and 25-hydroxyvitamin D2 [25(OH)D2] as the most common metabolites measured in human serum. Total vitamin D concentrations in human serum are typically in the 16 ng/g to 30 ng/g (40 nmol/L to 75 nmol/L) range, with 25(OH)D3 usually accounting for more than 90 % of the total. An epimer of 25(OH)D3, 3-epi-25(OH)D3, can be present at levels up to 10 % of 25(OH)D3 concentration. Seven National Metrology Institutions participated in the Track C Key Comparison CCQM-K132 Low-Polarity Analytes in a Biological Matrix: Vitamin D Metabolites in Human Serum. Participants were requested to evaluate the mass fractions, expressed in ng/g, of 25(OH)D3, 25(OH)D2, and 3-epi-25(OH)D3 in two human serum materials, termed Serum Pool I and Serum Pool II. Due to the known low levels of 3-epi-25(OH)D3 in both materials and the very low level of 25(OH)D2 in Serum Pool I, the study protocol stated that Key Comparison Reference Values (KCRVs) would be assigned only to 25(OH)D3 in both materials and 25(OH)D2 in Serum Pool II. Results for 3-epi-25(OH)D3 were requested to evaluate the separation technologies employed; 3 epi-25(OH)D3 needs to be chromatographically separated from 25(OH)D3 for proper quantification of 25(OH)D3. Results for 25(OH)D2 in Serum Pool I were requested to explore measurement performance at its low level. All of the participants used isotope dilution liquid chromatography with tandem mass spectrometry detection (LC


CCQM-K132, Key Comparison, SRM 2973, Vitamin D metabolites


Wise, S. , Tai, S. and Duewer, D. (2017), CCQM K132 Low-Polarity Analytes in a Biological Matrix: Vitamin D Metabolites in Human Serum, bipm, [online],, tbd (Accessed April 18, 2024)
Created September 14, 2017, Updated October 12, 2021