Vitamin D

D

What is measured?

Synonyms: 25-hydroxyvitamin-D3 (25OH-D3), 25-hydroxycholecalciferol, calcifediol, calcidiol; 25-hydroxyvitamin-D2 (25OH-D2), 25-hydroxyergocalciferol.
25-hydroxyvitamin-D3 and 25-hydroxyvitamin-D2 (1).
Method(s): LC-MS/MS.

Indication(s)

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

Protected from light, frozen, on dry ice (for general instruction on transportation, click here)

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.

Literature

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.

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