Reference interval for serum concentration of small dense low-density lipoprotein cholesterol in the healthy Japanese population

Small dense low-density lipoprotein a smaller and denser subfraction among whole low density lipoprotein particles is known to be highly atherogenic. The reference interval (RI) is not strictly defined for serum concentration of sdLDL-cholesterol (sdLDL-C) in Japan. The purpose of this study is to set the reference interval for sdLDL-C in healthy subjects.The population of this cross-sectional study was consisted of 40,862 individuals who had annual health checkups, and healthy subjects were extracted based on exclusion criteria such as medical history, social history, and blood sampling test results. Their serum sdLDL-C values were statistically analyzed and the RIs were set in men, premenopausal women, and postmenopausal women separately.The mean values of serum sdLDL-C in healthy subjects were 23.9 mg/dL in men, 20.0 mg/dL in premenopausal women and 23.7 mg/dL in postmenopausal women, and the RIs were 12.6-45.3 mg/dL in men, 11.4-35.1 mg/dL in premenopausal women and 14.6-38.6 mg/dL in postmenopausal women. Serum sdLDL-C values were significantly higher in men than in women. Besides, sdLDL-C values were significantly higher in postmenopausal women than in premenopausal women. In both genders, sdLDL-C values tended to increase with age.These results suggest that the RIs for sdLDL-C are recommended as follows: 13-45 mg/dL in men, 11-35 mg/dL in premenopausal women, and 15-39 mg/dL in postmenopausal women, respectively. Aside from these RIs, it is also necessary to define clinical cutoff values graded according to individual risk levels for atherosclerotic cardiovascular diseases.