The value of hip circumference/heightx ratio for identifying childhood hypertension

To investigate the value of hip circumference related indexes for identifying childhood hypertension. In 2011, 1,352 Han children aged 7–12 years were recruited in our study. Hypertension was defined as systolic blood pressure or diastolic blood pressure ≥95th percentile for all three screenings. We set the power value of the hip circumference/heightx ratio (x = 0, 0.8, 1 and 1.5) and studied the association with blood pressure. Hip circumference, hip circumference/height0.8, hip circumference/height and hip circumference/height1.5 all showed a positive correlation with systolic blood pressure and diastolic blood pressure(P < 0.05). Area under the curve (AUC) was used to evaluate the abilities of hip circumference related indexes. Hip circumference/height0.8, hip circumference/height and hip circumference/height1.5 were not superior to hip circumference. The present study demonstrates that hip circumference measurement is a helpful tool to detect the presence of hypertension in Han children 7–12 years old.

performed with MedCalc 11.4.2.0 software (Ostend, Belgium). Multiple linear regression analyses were performed to examine the relationships between blood pressure and other variables(sex, age, height, WC and hip circumference). Six models were used, Model 1: sex and age; Model 2: sex and height; Model 3: sex, age and height; Model 4: sex, age, height and WC; Model 5: sex, age, height and hip circumference; Model 6: sex, age, height, WC and hip circumference. Multiple linear regression analyses were also performed to examine the relationships between hip circumference and other variables(sex, age, height and WC). Four models were used, Model 1: sex and age; Model 2: sex and height; Model 3: sex, age, and height; Model 4: sex, age, height and WC. SPSS 11.5 statistical software (SPSS 11.5 for Windows; SPSS, Inc., Chicago, IL) was used for data analysis. P < 0.05 was considered statistically significant.
Results 36 children(16 boys and 20 girls) were diagnosed as hypertension. Anthropometric parameters were shows in Table 1. Compared with girls, the levels of hip circumference, hip circumference/height 0.8 , hip circumference/ height and hip circumference/height 1.5 were higher in boys (P < 0.001). As shown in Table 2, age, height, BMI, waist circumference, hip circumference, hip circumference/height 0.8 , hip circumference/height and hip circumference/height 1.5 positively correlated with systolic blood pressure(SBP) and diastolic blood pressure(DBP), boys and girls both(P < 0.05).

Discussion
This study discusses the use of hip circumference related indexes in the evaluation of children hypertension in Han race aged 7-12 years. Hip circumference related indexes were closely related with blood pressure for both boys and girls. Thus, hip circumference related indexes can accurately identify hypertension in Han children.
Increasing evidence has demonstrated that BAI positively correlated with blood pressures in adults, but not superior to BMI [8][9][10][11] . BAI and BMI were significant predictors of risk of hypertension and changes in blood pressure after an 8-years follow-up 12 . Dong et al. found that BMI could be a better predictor of elevated BP than BAI in Chinese children and adolescents 13 . Comparing with the traditional obese indexes, BMI and WC, BAI was not superior in identifying hypertension, especially in boys.
The result is likely related to the following mechanism. Obesity is key feature in the pathophysiology of hypertension in children. BMI and WC are two common indexes of obesity. BAI is another index for evaluating obesity calculated from measurements of the hip and height. Two studies from china showed that BMI and WC are better tools than BAI for estimating whole body fat and central body fat in Chinese adults and children 14,15 .
BAI was proposed in adults and over-estimated the percentage of body fat in children 5 . El Aarbaoui T et al. proposed BAIp. BAIp appears as a new index for children's body fatness, with acceptable accuracy. Hip circumference/height ratio and BAIp are better markers for overweight (adiposity) in obese children than BAI 16 . However BAIp do not provide better estimate of obese children's adiposity and metabolic complications than the widely used BMI and WC 16,17 . In our study, the AUCs of hip circumference/height ratio and BAIp were improved than the AUCs of BAI while there is not statistical difference. But the AUCs of BMI, WC, hip circumference/height ratio and BAIp were similar in boys and girls. The result means that the abilities of these indexes were alike for identifying children hypertension. Moreover, all hip circumference related indexes were not superior to hip circumference. In other words, hip circumference related indexes were not improved after adjustment for height and complicated calculation. Hip circumference itself is simple and accuracy.
The determinants of childhood blood pressure include height and adiposity 18,19 . The role of height is a normal growing process. So the diagnostic criteria of the children hypertension is a set of age-, sex-and height-specific  criteria of blood pressure. The role of adiposity is a pathological process. Consistent with previous studies 18,19 , the correlation between blood pressure and height was significant after age and sex adjustment and weakened after further adjusting for WC. The increase of blood pressure was due to the childhood normal body growth and adiposity.
Interesting, the correlation between height, WC and blood pressure was not significant after adjusting for hip circumference. In our study, multiple linear regression shows that hip circumference was independent related with age, height and waist circumference. At a young age, children not only grow up, but also expand hip circumference. It is a normal growing process. At the same time, many studies found that hip circumference associated with visceral fat area in children 20,21 . It means that hip circumference can reflects childhood normal body growth and adiposity.
The children of the study were Han race. The range of age was 7-12 years old. The ability of hip circumference related indexes for identifying childhood hypertension should be further confirmed in different races and age groups.
In conclusion, hip circumference measurement is a helpful tool to detect the children with hypertension in Han race 7-12 years old. Compared with BAI and BAIp, hip circumference is more simple.