Objective: To probe into the reference values of 25-hydroxy vitamin D (25OHD) in healthy children aged from 0 to 3 years in Chongqing. Methods: According to inclusion and exclusion criteria

a total of 900 healthy children aged from 0 to 3 years with physical examination in child health care department of different hospital from districts/counties in different regions representing different economic levels of Chongqing were extracted. Venous blood was extracted

serum was separated

and serum 25OHD concentration was detected by high performance liquid chromatography-mass spectrometry (LC-MS). Physical examination and questionnaire survey were conducted for each respondent at the same time. Results: The reference values of serum 25OHD in children aged from 0 to 3 years in Chongqing was (34.99±20.27) ng/mL. There was no significant difference in the levels of 25OHD between girls and boys (u=-1.327

P=0.185). The levels of25OHD in the <1 year group were higher than those in the 1 to 3 year group (u=2.062

P=0.040). The levels of 25OHD in winter and spring were lower than those in summer and autumn (u=-4.299

P=0.000). Conclusion: The reference values of serum 25OHD in children aged from 0 to 3 years in Chongqing was (34.99±20.27) ng/mL. The 25OHD levels in healthy infants varied by age and season. The range of reference values obtained in this study is basically consistent with the global expert consensus and the recommended value of the IOM in the United States

which provides objective evidence for vitamin D supplementation and diagnosis of vitamin D deficiency-related diseases in infants.