Optimal monitoring time interval between DXA measures in children

Abstract

Purpose The monitoring time interval (MTI) is the expected time in years necessary to identify a change between two measures that exceeds the measurement error. Our purpose was to determine MTI values for dual-energy X-ray absorptiometry (DXA) scans in normal healthy children according to age, sex, and skeletal site. Methods 2014 children were enrolled in the Bone Mineral Density in Childhood Study and had DXA scans of the lumbar spine, total hip, non-dominant forearm, and whole body. Measurements were obtained annually for seven visits from 2002 to 2010. Annualized rates of change were calculated by age and sex for all bone regions. A subgroup of 155 children ages 6 to 16 years (85 boys) had duplicate scans for calculation of scan precision. The bone mineral density (BMD) regions of interest included spine, total body less head (TBLH), total hip, femoral neck, and 1/3 radius. Bone mineral content (BMC) was also evaluated for spine and TBLH. Percent coefficient of variation (%CV) and MTI were calculated for each measure as a function of age and sex. Results MTI values were substantially less than 1 year for TBLH and spine BMD and BMC for boys ≤ 17 years and girls ≤ 15 years. Hip and 1/3 radius MTIs were generally 1 year in the same group. MTI values as low as 3 months were found during the peak growth years. However, MTI values in late adolescence for all regions were substantially longer and became nonsensical as each region neared the age for peak bone density. Conclusion All 4 DXA measurement sites had reasonable (< 1 year) MTI values for boys ≤ 17 years and girls ≤ 15 years. MTI was neither useful nor stable in late adolescence and young adulthood. Alternative criteria to determine scan intervals must be used in this age range.

Bone Densitometry in Children and Adolescents

“…The "least significant change" refers to the smallest percentage difference in measurements that exceeds the variability or "noise" from repeated measurements. 24 In densitometry centers that are able to perform a precision study, a least significant change of 3% or less usually can be achieved. 24 However, some hospital radiation safety committees prohibit DXA centers from carrying out these protocols.…”

“…24 In densitometry centers that are able to perform a precision study, a least significant change of 3% or less usually can be achieved. 24 However, some hospital radiation safety committees prohibit DXA centers from carrying out these protocols. It should also be recognized that interval growth changes and accompanying increases in bone size make it more difficult to differentiate true increases in density from changes in areal BMD that are related to growth.…”

Assessment of Bone Health in the Young Athlete

“…A recent study demonstrated that precision error of DXA scans varies with region of interest, age, and sex. For girls 17 years and younger, a monitoring time interval of 1 year enabled identifi cation of DXA changes that exceeded precision error [ 33 ]. Until further information becomes available, for most adolescents and young adults, it is reasonable to repeat the DXA measures after 1 year.…”

A double-blind, randomized, Phase III, multicenter study in 358 pediatric subjects receiving isotretinoin therapy demonstrates no effect on pediatric bone mineral density

“…Multiple studies with similar average treatment doses to those reported in this study have not demonstrated a decrease in the lumbar spine and hip BMD using dual X-ray absorptiometry (DXA) in pediatric or adult subjects [7][8][9][10][11]. A single-center study in [17][18][19][20][21][22][23][24][25] year-old men identified no significant difference in the spine or femoral neck BMD; however, a decrease in Ward's triangle BMD was described [2]. This finding in Ward's triangle is of dubious clinical significance, as this site is not used to diagnose osteoporosis in the pediatric years due to geometry changes during growth [12,13].…”

“…Six months is the minimum interval between scans, as recommended by the International Society of Clinical Densitometry (ISCD) [19]. However, a recent study evaluating DXA monitoring time interval (MTI) in a population of normal subjects suggests that in subjects from 12-17, MTI varied from 0.1 to 0.5 years [21]. This suggests that the expected BMD change in this study population would be detectable at 5.5 months.…”