James R. Hansen

Cross-validation of the slaughter skinfold equations for children and adolescents

Prior to sexual maturation, children and adolescents have more water and less bone mineral content than adults, resulting in less dense fat-free body mass (FFM). This suggests that previously established adult skinfold/density equations are inappropriate for use with children and adolescents for the prediction of body fatness (%BF) and FFM. To overcome this problem, Slaughter and colleagues have introduced new skinfold (SKF) equations that take into account the changing density of FFM in children and adolescents as they mature. The purpose of our study was to cross-validate a select set of the Slaughter SKF equations by comparing them with a criterion measurement (Lohmans Siri age-adjusted body density equation) in 122 subjects ranging in sexual maturation from pre- to post-pubescent and ranging in age from 8-17. Our cross-validation found very high intraclass (reliability) correlations (ICCs = 0.98-0.99) and high validity correlations (rs = 0.79-0.99). The standard errors of the estimate for %BF ranged from 3.5-4.6% and total errors for %BF ranged from 3.6-4.6%. The Slaughter equation using tricep and calf SKF for females was significantly different (P < 0.05) from the criterion measure in its prediction of %BF. In males, there was an interaction between the SKF equation and subject maturation level. The data indicate that the Slaughter SKF equations hold promise for estimating body composition in children and adolescents but are still in need of refinement.

Criterion methods of body composition analysis for children and adolescents

The lack of chemical maturity, subsequent to normal growth and maturation, complicates the assessment of body composition in children. Even though known to overpredict percent body fat (%BF), the use of adult prediction equations is widespread in the pediatric literature. Many sex‐ and age‐specific modified equations have been proposed. This study reports a cross‐validation analysis of selected laboratory‐based criterion methods in an attempt to identify the most appropriate reference which could be used in future validation studies of the more practical field/clinical testing methods. Subjects were 48 (24 boys and 24 girls) peripubertal children evenly distributed according to stage of maturation. Criterion measurements included body density (Db) by hydrostatic weighing, total body water (TBW) by deuterium oxide dilution, and total body mineral content (TMC) by dual energy x‐ray absorptiometry. Five different prediction models were evaluated. Test‐retest reliabilty was high (ICC = .970 to .999). Of the prediction models tested, the four‐component model was considered the most accurate laboratory‐based criterion model since it involves measurement of the primary constituents of fat‐free mass. Based on high r2 (≥.942) values, low standard errors of estimate (SEE = 1.8 %BF males, 1.1 %BF females); and low total prediction errors (TE = 1.9 %BF males, 2.0 %BF females), the Lohman age‐adjusted prediction equation showed the best agreement with the four component model. If multiple testing facilities are unavailable, the Lohman two‐component (Db) model would be the criterion method of choice.

Clinical Management Issues in Males with Sex Chromosomal Mosaicism and Discordant Phenotype/Sex Chromosomal Patterns

The recent availability of Y DNA probes has made it possible to identify two forms of 46,XX male syndrome: Y DNA positive and Y DNA negative. The Y DNA positive male results from a X;Y translocation with a low recurrence risk; the Y DNA negative males are due to a mutation with a high recurrence risk. 46,XX males and mosaic forms are phenotypically indistinguishable. A review of the case histories for 11 individuals indicates that affected males have highly variable genital and nongenital phenotypes. Physical findings may be clearly apparent or nonexistent. With the exception of external genitalia, the basis for this variability is unknown. It may be related to differences in Y chromatin expression as the result of variable inactivation of the X chromosomes, or to the existence of minor deletions or point mutations secondary to an exchange of genetic material. Common and uncommon clinical problems in these individuals require evaluation and follow-up care that is provided through a cooperative, interdisciplinary approach.

Measurement of Pulsatile Hormone Release from Perifused Pituitary Cells Immobilized on Microcarriers

Publisher Summary This chapter discusses a method for measurement of pulsatile hormone release from perifused pituitary cells immobilized on microcarriers. Following cervical dislocation and decapitation, pituitaries are removed from weanling female Sprague-Dawley rats and collected in a 50-ml conical centrifuge tube containing fresh, sterile media (M199/BSA). The pituitaries are rinsed several times with M199/BSA and placed in a Petri dish, where each pituitary is cut into 6–8 pieces using a sterile razor blade. The pituitary pieces are allowed to settle in fresh M199/BSA in a sterile centrifuge tube. The M199/BSA is decanted and replaced twice with fresh M199/BSA to remove lysed cells and their products. After centrifugation of the cell filtrate at 225 g for 10 min at 23°C, the supernatant is discarded and the pellet is resuspended in culture medium. A cell suspension aliquot of 0.55 ml is delivered to each cell chamber. Culture medium is added to bring the final volume of each cell chamber to 1.0 ml. The cell chambers are gently shaken to mix the cell suspension and the microcarriers. Cell viability, which is assessed by Trypan blue dye exclusion, is typically in excess of 95% at the completion of the dispersion.