Effects Of Sample Size On Bone Mineral Density Reference Databases And Differences In Bone Mass Of Hip Between Different Ethnic Women

Chapter one Effects of the sample size of reference population on determining BMD reference curve,peak BMD and diagnosing osteoporosisObjective To explore the effect of sample size of reference population on establishing bone mineral density(BMD)reference databases.Subjects and Methods The total reference population consisted of 3662 females from Changsha,aged 6～85 years.BMD was measured with a dual-energy x-ray absorptiometry densitometer.The subjects were randomly divided into 4 different sample groups,that is,total number(Tn) = 3662,1/2 n = 1831,1/4 n = 916,and 1/8 n = 458.We used the best regression model to determine age-related BMD reference curve,the peak BMD and the reference plot.We also compared the current reference databases with the NHANES reference databases provided by the densitometer.Results At each skeletal site,the cubic regression model was always the best one to fit BMD change with age for the 4 sample groups. There was no significant difference in the full curves between the 4 sample groups at each skeletal site,although some discrepancy at the end of the curves was observed at the spine.The peak BMDs and their standard deviations(SD)were very similar between the 4 sample groups. The reference plots consisted of the fitted curves±2SD were also similar. According to the Chinese diagnostic criteria(BMD loss＞25%of the peak BMD),no difference was observed in the osteoporosis detection rates of the subjects aged 50～85 years using the reference values determined by the 4 different sample groups,whereas some differences appeared according to WHO diagnostic criteria(T≤-2.5).The BMD reference curves and osteoporosis detection rates by our current reference values were significantly lower than their of the NHANES reference databases.Conclusion Varying the sample size from hundreds to thousands has no decisive effect on determining BMD reference curves,the peak BMDs,the reference plots and diagnosing of osteoporosis according to Chinese percent diagnostic criteria.It should be practical for determining the reference population while establishing BMD databases.Chapter two Differences in age-related bone mass of hip between Chinese women and different ethnic women in the United StatesObjective To explore the differences in age-related bone mass and bone loss rate of hip between native Chinese women and women of different races in the United States.Subjects and Methods We measured bone mineral density(BMD), bone mineral content(BMC)and bone area(BA)with dual-energy x-ray absorptiometry bone densitometer in different regions of hip in 3614 Chinese women,aged 20 years and older,and calculated the volumetric BMD(vBMD)at the femoral neck.The best regression models were chosen to fit the changes of these parameters with increasing age. Subsequently,we compared these fitting curves to the full-matched data of non-Hispanic blacks,non-Hispanic whites and Mexican Americans women reported by the third National Health and Nutrition Examination Survey(NHANESⅢ).Results We found that the fitting curves of BMD and BMC of Chinese women were significantly lower than those of women of races in the United States(P=0.001～0.000);and those of non-Hispanic blacks were highest among the four races(P=0.000).However,when the expression of difference was transformed from BMD to vBMD at femoral neck,the difference between Chinese women and non-Hispanic blacks reduced from 22%to 18%,between Chinese women and non-Hispanic whites from 7.4%to 0.8%,but the difference enlarged from 3.2%to 9.6% between non-Hispanic whites and Mexican-Americans,from 13%to 17% between non-Hispanic whites and blacks.By the age of 80 years,the accumulated bone loss rate in various regions of hip for Chinese women, Mexican-Americans,non-Hispanic whites and blacks women were -38.9±1.8%,-34.4±3.1%,-27.8±5.9%and -28.4±4.8%,respectively.Conclusion The bone mass of native Chinese women in hip is significantly lower,and bone loss rate larger than those of non-Asian women in the USA.But at femoral neck,the vBMD of Chinese women is similar to that of non-Hispanic whites.