Study population
All enrolled study participants were part of the GDDSD study (Growth and Development Diseases in Shandong Province: an observational, ongoing prospective, open cohort follow-up study, http://www.chictr.org.cn, ChiCTR1900026510) [16]. The participants were children and adolescents with short stature who were hospitalized in the Endocrinology Department of the Affiliated Hospital of Jining Medical University between April 2020 and February 2022 and underwent BIA and two GH stimulation tests. The authors had access to information that could identify individual participants during or after data collection. The inclusion criterion was a height more than two standard deviation scores (SDS) lower than the average height of people of the corresponding age and sex [3]. The following patients were excluded: (1) patients without GH stimulation test results or IGF-1; (2) patients with chronic organic diseases, autoimmune diseases, metabolic abnormalities, malignant tumors, or thyroid dysfunction; (3) patients with skeletal diseases, such as achondroplasia, skeletal dysplasia, and sexual development disorders; and (4) patients with BIA contraindications, such as metal or electronic implants (atrial pulse generator or pacemaker).
The proposal was reviewed and approved by the Human Ethics Committee of the Affiliated Hospital of Jining Medical University, and all methods were performed in accordance with the guidelines of the Declaration of Helsinki. The patients’ families were informed of the aims of the study, and written informed consent was obtained from the patients’ parents.
Anthropometric Measurements Of Body Composition
Body composition, including body fat, total body moisture, protein, skeletal muscle, and other health indices, which can effectively reflect the health status of the human body, was measured using BIA. The temperature of the indoor environment was maintained at 20–25 ℃. The participants were in a quiet and fasting state before the test. Afterward, the participants were required to step on the electrode plate with bare feet and hold the contact or adhesive electrodes on both sides with both hands so that the body composition could be measured. The percentage of body fat (PBF) refers to the proportion of body fat in the total body weight, also known as the percentage of body fat, which reveals the body fat content [17]. The fat mass index (FMI), free fat mass index (FFMI), and skeletal muscle index (SMI) were calculated by dividing fat mass, lean body mass, and skeletal muscle mass by height squared, respectively.
Laboratory Measurements
A fasting blood sample was obtained from all participants, and laboratory parameters were measured according to our previous study method [16]. To assess the peak of GH, two of three GH stimulating tests were performed using different mechanisms (500 mg of levodopa for those weighing ≥ 30 kg and 250 mg of levodopa for those weighing < 30 kg (orally) and 0.1–0.15 U/kg insulin (subcutaneously) or 0.5 mg/kg arginine). Both blood glucose and GH levels were monitored at 0, 30, 60, 90, and 120 min, respectively. GH was measured using a chemiluminescence method (ACCESS2, Beckman Coulter; USA) with an analytical sensitivity of 0.010 µg/L. The biochemical and immune indices extracted from the hospital laboratory included hemoglobin (Hb), alanine aminotransferase (ALT), albumin (ALB), creatinine (Cr), triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), blood calcium (Ca), blood phosphate (P), free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), IGF-1, and IGF-binding protein-3 (IGFBP-3). The SDS of IGF-1 was calculated based on the normal reference value of healthy children and adolescents of the same age and sex [18]. All methods were performed in accordance with the relevant guidelines and regulations.
Statistical analysis
SPSS Statistical (26.0; IBM Corp, Armonk, NY, USA) was used for statistical analysis. The continuous variable with normal distribution was expressed as \(\bar {\chi } \pm {\text{SD}}\), while the continuous variable with non-normal distribution was expressed as the median and interquartile range. In addition, categorical variables were indicated by frequency or percentage. Comparisons between groups were conducted using the independent t test, Mann–Whitney U test, and chi-square tests. Correlation analysis was performed by utilizing Pearson’s correlation coefficient. Multiple stepwise linear regression analysis was applied to verify independent factors associated with body composition. Statistical significance was set at P < 0.05.