Background: The demand for vitamin D testing is increasing in China. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) immunoassay is specific and accurate but requires expensive equipment, experienced operators, and complicated pretreatment of serum. Automated immunoassays are simple and convenient but only determine total 25-hydroxyvitamin D (25OHD). The objective of this study was to quantify 25OHD2 and 25OHD3 in patients to assist clinical physicians and laboratory directors in choosing the most appropriate method to determine 25OHD.
Methods: Vitamin D testing was conducted for 23,695 patients in Peking Union Medical College Hospital from May 2015 to January 2017. Using this large data set, the prevalence and levels of 25OHD2 were analyzed. LC-MS/MS was used to separately determine 25OHD2 and 25OHD3.
Results: 25OHD2 (≥2.5 ng/mL) was detected in 16.4% (3877/23,695) of patients. Males had a significantly lower incidence of detectable 25OHD2 (p<0.01); 1077 (13.9%) samples contained detectable 25OHD2 (median: 3.7 ng/mL; 2.5%-97.5%: 2.5-17.2 ng/mL). For females, 2800 (17.5%) samples contained detectable 25OHD2 (median: 4.0 ng/mL; range: 2.5-20.6 ng/mL). Of the 3877 patients with detectable 25OHD2, males had a significantly higher level of 25OHD3 (p<0.01). There was no significant difference in total 25OHD. The proportion of 25OHD2 in total 25OHD was 1.3%-100%; 87.5% (3391/3877) of the samples contained <10 ng/mL 25OHD2. 25OHD2 negatively correlated with 25OHD3 (r=-0.197, p<0.01) and positively correlated with total 25OHD (r=0.217, p<0.01).
Conclusions: Prevalence of 25OHD2 in patients tested for vitamin D is relatively high in China. 25OHD2 is significantly negatively correlated with 25OHD3.
Keywords: 25OHD2; 25OHD3; immunoassay; liquid chromatography-tandem mass spectrometry; vitamin D.