The objective of this growth utility program is to predict a child's bone mineral content at four sites in the body. Dual-Energy X-ray absorptiometry (DXA) has become the standard technique for the measurement of bone mineral content (BMC) of the lumbar spine, femur and total body. The comparison of an individual's value with a reference range has gained the most widespread clinical use. In adults, one of the most common comparisons is the z score. A z score compares the difference between an actual measure and a predicted measure as a ratio of the variance of the measure. The z score therefore provides a comparison with healthy subjects of the same chronological age. In children a z score that only accounts for age is inappropriate because it does not account for the wide variations in growth patterns occurring during childhood, nor does it account for racial differences. Furthermore, the predictive equation has to be able to capture individual children's differences in growth rates.
Data from the PBMAS was combined with longitudinal data from the following studies: The University of British Columbia's Healthy Bones Trials, Penn State University's Young Women's Health Study, and Stanford University's Bone Mineral Accretion Study. To predict BMC the following variables are required, gender, date of birth, date of measurement, height, weight and race (either White, Asian, Black or Hispanic). Gender, race and age site specific anthropometry-based longitudinal model predictions of BMC are produced.1 BMC for four sites (Total body BMC(TBBMC), Total Femoral Hip BMC (TFHBMC), Femoral Neck BMC(FNBMC), and Lumbar Spine (L2-L4) (LSBMC)) are predicted from measurement of BMC using a Hologic QDR-4500 instrument. If a site specific measure of BMC from a Hologic QDR 4500 instrument is available for the child then a Z score for the individual is calculated. Accuracy of the measurements is of paramount importance, as any errors will dramatically alter the precision of the prediction. Detailed descri ption of the measurement protocols can be found here.
1 Baxter-Jones, A.D.G., Burrows, M., Bachrach, L.K., Lloyd T., Petit, M., Macdonald, H., Mirwald R.L. Bailey, D., McKay, H. 2010. International longitudinal paediatric reference standards for bone mineral content. Bone, 46, 208-216
- This utility is designed for use in pediatric populations between the chronological age range of 8 to 16 in females and 9 to 18 in males and a maturity age range of -4 to + 4 years from peak height velocity. Any predictions outside these age ranges will be associated with a degree of error in the prediction and therefore will not be calculated.
- Accuracy of the measurements input into the predictions is of paramount importance, especially for the variable sitting height. Large measurement error will be associated with a degree of error in the prediction. (For a description of measurements methods, please see the Measurements Protocol page.)
- Prediction of age at peak height velocity is only appropriate prior to the event and two years after the event. In boys this is roughly between 12 and 16 years and for girls 9 to 13 years. The further away from the event the greater the error in the prediction.
- Predictive equations for age at peak height velocity and adult height are based on a normal, white Caucasian population. Predictions in other races may be associated with a degree of error in the prediction.
- Prediction of Bone Mineral Content (BMC) at the four bone sites provides specific racial equations (Caucasian, Asian, Black and Hispanic) for a Hologic QDR-4500 instrument only.
- This utility will only work if the 'Date of Test' is earlier than the current date and time in the Central/Mountain time zone. The current date and time is 12-Mar-15, 09:53 AM