with end-organ failure. There were 81 children identified who met the inclusion criteria: 18 years of age or younger, on the kidney, liver or intestine transplant list with end-organ failure, and a CT scan within 6 months of actual transplant date. Data were included from 2002 to 2012.
Control patients were chosen anonymously from the trauma center database. Subjects and controls were matched 1:1 for gender and age. Within each gender and age group, controls were chosen as the patient closest to the 50th percentile nationally for height and weight. A male and female control were selected for every six months of age from age 6 months until age 3, then one male and female control for every 1 year of age for ages 4 to 18. Each organ failure patient was matched to a control of the same gender, and the one closest to the subject in age.
All CT measurements were completed by trained research assistants with experience in reading CT images. Measurements were taken at the level of the L2/L3 intervertebral disc space as shown in Figure 1A which has been routinely employed as an accurate approximation of total body composition.[1] Within the imaging software, the scan was set to the soft tissue image mode and the free hand drawing tool was employed to outline the target structures. Total psoas muscle area was obtained by outlining both the right and left psoas muscles as seen in Figure 1B and summing these measurements. Total perinephric fat was calculated by outlining the kidney and vasculature and subtracting this area from the area obtained by outlining Gerota’s fascia as shown in Figure 1C. Perinephric fat was not measured in kidney failure patients because of marked kidney atrophy or absence. If the patient had only one kidney, then the measurement of the perinephric fat for the existing kidney was simply doubled. Likewise, the subcutaneous fat area was obtained by subtracting the area of the outlined abdominal cavity (at the outer-most
fascial layer) from the area obtained by outlining the level just beneath the dermis as shown in Figure 1D. Measurements were made by two unbiased observers, unaware of patient diagnosis
and clinical outcome, to establish inter-rater reliability. Each measurement was made
independently with the technician blind to the data collected by the other rater. Measurements that differed by more than 15% between the raters were reviewed jointly until a consensus was reached. The mean value between the observers was used in statistical analysis. In order to account for variations due to differing patient heights, all measurements were scaled for height.
Height, weight and laboratory values were extracted from the database to coincide with the timing of the CT scan. The sarcopenic index was obtained by dividing the total psoas area (in mm2) by the height (in cm) squared. Likewise, the visceral and subcutaneous fat measurements were scaled for height. The scaled measurements of the transplant patients were compared to the scaled measurements of age-matched controls. The difference was calculated by subtracting the control measure from the transplant patient measure and a percent difference was calculated. A subgroup analysis was performed using age and gender. Age subgroups were created to reflect changes in pediatric BMI curves (ages 0-4, 5-12, 13-18). Tests for skewness and kurtosis showed a normal distribution of the data allowing parametric testing to be used in the statistical analysis (t-test). A p-value could not be calculated in the age group sub-analysis for the kidney and intestine patients because the numbers in some age groups were too small. CT images were viewed and measured using Synapse picture archiving and communication system (PACS) software (FUJIFILM Holdings America Corporation, Valhalla, New York, USA). Data were analyzed using Statistical Package for the Social Sciences (IBM SPSS Statistics 23, IBM Corporation, Armonk, New York, USA). Retrospective analysis of patient data for this study were reviewed and approved by the Institutional Review Board of the Indiana University School
of Medicine.
References
1. Prado, C.M. and S.B. Heymsfield, Lean tissue imaging: a new era for nutritional assessment and intervention. JPEN J Parenter Enteral Nutr, 2014. 38(8): p. 940-53.
Figure legend
Figure 1a. Computed tomography axial image taken at the level of the L2/L3 intervertebral disc space.
Figure 1b. Total psoas muscle area was calculated by outlining both the right and left psoas muscles areas and summing the results.
Figure 1c. Total perinephric fat area was calculated by subtracting the area of the outlined right and left kidneys, and their vasculature, from the area measured by outlining Gerota’s fascia. The perinephric fat area for the two kidneys was summed.
Figure 1d. Subcutaneous fat area was calculated by subtracting the area of the outlined
abdominal cavity (at the outer-most fascial layer) from the area obtained by outlining the level just beneath the dermis.
