Synonyms: 25-hydroxyvitamin-D3 (25OH-D3), 25-hydroxycholecalciferol, calcifediol, calcidiol; 25-hydroxyvitamin-D2 (25OH-D2), 25-hydroxyergocalciferol.
What is measured: 25-hydroxyvitamin-D3 and 25-hydroxyvitamin-D2 (1).
Performance of the assay
Lower limit of detection (LOD) (25OH-D3/25OH-D2): 3.3/3.3 nmol/L.
Within-day CV: 4-5/4-5 %; between-day CV: 7-8/5-8 %.
Assessment of vitamin D status. 25OH-D3 and 25OH-D2 are the main circulating vitamin D forms. 25OH-D3 is most abundant and the important marker of vitamin D status, whereas 25OH-D2 is detected in a small portion of individual, is mainly derived from supplements, and may be inversely related to 25OH-D3 (2).
Specimen, collection and processing
Patient/subject: Vitamin D levels show a high level of seasonality due to the influence of sunlight.
Matrix: Serum or EDTA plasma.
Volume: Minimum volume is 50 µL, but 200 µL is optimal and allows reanalysis.
Preparation and stability: Samples should be put on ice, and protected from light.
Transportation; for general instruction on transportation, click here.
Frozen, on dry ice.
Reported values, interpretation
Reported values (25OH-D3/25OH-D2): 20-150/0-4 nmol/L.
To convert from SI unit (nmol/L) to conventional unit (µg/L), multiply the SI value by the conversion factor = 0.4011. Intraclass correlation coefficient (ICC) (25OH-D3/25OH-D2): 0.71/na.
1. Midttun, Ø., McCann, A., Aarseth, O., Krokeide, M., Kvalheim, G., Meyer, K., and Ueland, P.M. (2016). Combined measurement of 6 fat-soluble vitamins and 26 water-soluble functional vitamin markers and amino acids in 50 μL of serum or plasma by high-throughput mass spectrometry. Anal Chem 88, 10427-436.
2. Yu, S., Zhang, R., Zhou, W., Cheng, X., Cheng, Q., Xia, L., Xie, S., Yin, Y., Sun, D., et al. (2018). Is it necessary for all samples to quantify 25OHD2 and 25OHD3 using LC-MS/MS in clinical practice? Clin Chem Lab Med 56, 273-77.