Objective:To analyze the level of homocysteine (HCY) and its influencing factors in different ethnic groups in Lhasa, and to explore its reference interval.Methods:Reference interval study. The serum HCY (μmol/L) level of 820 healthy subjects was analyzed in Tibet autonomous region People′s hospital from January to December 2018. All the subjects were divided into groups according to ethnicity, gender, age and season. The general linear model was used to analyze the differences in serum HCY levels groups. According to the CLSI C28 document, the Nested ANOVA and Z test were used to analyze and determine whether or not different groups need to establish the reference interval. Results:Ethnicity, age and gender had significant effects on serum HCY. The level of HCY in Tibetan was higher than that in Han (P<0.001); the level of Hcy in male was higher than that in female ( P<0.001); the level of HCY in over-50 year old group was higher than that in under-50 year old group ( P=0.01). There was no significant difference in serum HCY level in seasonal distribution ( P=0.22). Nested ANOVA and Z tests confirmed that the HCY reference interval in Lhasa should be established according to ethnicity and gender in clinical application. The reference interval of HCY level in Lhasa area was established according to difference genders, including<22.41 μmol/L for Tibetan men,<18.41 μmol/L for Tibetan women. Conclusions:The serum HCY levels of the apparent healthy people in Lhasa area were slightly different among people of different ethnicities, genders and ages. We established the reference intervals of HCY of different ethnic groups and gender groups in Tibet and our results have practical significance for the prevention and treatment of cardiovascular and cerebrovascular diseases at high altitude.