25-hydroxyvitamin D2 and D3 composition and repeat test patterns in routine adult hospital liquid chromatography-tandem mass spectrometry testing
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Yichi Mai1,2,3, Ziyin Song1,2,3, Cheng Yi1,2,3
1Department of Clinical Laboratory, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong, China.
Introduction:
Liquid chromatography-tandem mass spectrometry quantifies 25-hydroxyvitamin D2 (25[OH]D2) and D3 (25[OH]D3) separately, but clinical reporting often emphasizes total 25(OH)D. We characterized component composition and repeat test changes in routine adult hospital testing.
Methods:
We retrospectively analyzed a pseudonymized dataset derived from routine laboratory records for vitamin D tests performed from June 2019 through November 2022. Cross-sectional analyses used first tests from 2808 adults; longitudinal analyses compared first and last tests in 446 retested adults. Vitamin D2-contributory composition was defined exploratorily as a 25(OH)D2 share of at least 10%, with sensitivity analyses using 5%, 20%, and a continuous measure.
Results:
Median total 25(OH)D was 24.6 ng/mL (approximately 61.5 nmol/L), and 71.3% of results were below the local reference cutoff. Vitamin D2-contributory composition occurred in 16.3% and was associated with sex, season, and ordering service. Among retested adults, median changes were 4.3 ng/mL for total 25(OH)D, 4.2 ng/mL for 25(OH)D3, and -0.1 ng/mL for 25(OH)D2. Total change correlated with 25(OH)D3 change (ρ = 0.98; P < .001) but not with 25(OH)D2 change (ρ = 0.04; P = .46).
Discussion:
Fractionated measurements revealed compositional variation within total 25(OH)D categories and predominantly D₃-related changes on repeat testing. The clinical implications of these patterns require further evaluation.
