Appropriately established pediatric reference intervals are critical to the clinical decision-making process and should reflect the physiologic changes that occur during healthy child development. Therefore, female adolescents using oral contraceptives were not excluded from the reference population prior to calculating reference intervals for transferrin saturation. These values aligned closely with our reference intervals, which span from 4.1%-59% transferrin saturation. A total of 852 subjects had available data on both serum iron and transferrin concentrations, after excluding subjects based on the above stated criteria. This is due to several challenges that are encountered in establishing pediatric reference intervals, including small sample volumes and collecting blood from a sufficient number of healthy children and adolescents to cover the extensive periods of growth and development (3). Continuous reference intervals are a superior method for determining intervals where values vary with age. In this study, we demonstrated the calculation of continuous reference intervals for T, SHBG, and calculated free and biovailable T in males and females under the age of 20 using the quantregGrowth package. Only the Slim Guide® skinfold caliper did not require partial disassembly. It is noteworthy that adherence and accuracy to an updated anthropometric measurement technical protocol and use of a carefully selected skinfold caliper are essential for the reproducibility and reliability of skinfold thickness(1,10). Under the pseudonym Lipowise® and of Portuguese origin, the device was presented as the first generation of a digital and automated skinfold caliper with a stopwatch system and measurement recording integrated into a smartphone via Bluetooth connectivity(9). Later, in the 1980s, the first electronic skinfold caliper was introduced under the pseudonym Skindex®. Skinfold calipers (or "body fat calipers") are devices used to measure your body fat percentage (a caliper is any device that measures the dimensions of an object). Several reference intervals were reported from the CALIPER study and used the same study population and statistics but different analytical systems. For example, total testosterone concentrations for Tanner stage 1 are often slightly higher than those reported for male individuals who are about 5 years old because of inclusion of late prepubertal boys who may have early gonadarche or adrenarche. In male individuals, puberty typically begins after age 9 years when total testosterone concentrations start gradually rising and reach adult levels by the later stages of puberty, typically in the midteenage years. The secondary sex characteristics that develop during puberty are characterized according to Tanner stage.35 Clinically, E2 and total testosterone concentrations are assessed in the evaluation of pituitary diseases, irregular menses, suspected polycystic ovary syndrome, hypogonadism, and other diseases related to sexual development.36 Each PRI source was examined for information on the laboratory method used, population surveyed, statistical approaches used, covariates, and published reference intervals. Analytes commonly measured in the pediatric clinical setting were used as examples for this review and included the thyroid axis hormones free thyroxine (FT4) and thyrotropin, the kidney function biomarker cystatin C, insulin-like growth factor 1 (IGF-1), total testosterone, estradiol (E2), and the iron-status indicators hemoglobin and ferritin. It also requires significantly more effort and tends to slightly underestimate the body fat percentage of people who are fairly lean. That said, it tends to underestimate the body fat percentage of people who are fairly lean (men under 15% body fat and women under 25%). You can find all of the equations you need to calculate your body fat percentage below. Learning how to measure body fat with calipers takes practice, so here are five tips to help you get more accurate readings. Measuring body fat with calipers isn’t as tricky as some would have you believe. Although setting a body fat percentage goal can be motivating (e.g. "I want to get down to 20% body fat"), what matters most is that you’re happy with what you see in the mirror. Remember, too, that accurately measuring your body fat percentage isn’t necessary or even all that useful for getting into great shape. We then used these data to calculate age-, gender-, and Tanner stage-specific reference intervals according to Clinical Laboratory Standards Institute C28-A3 guidelines. While mass spectrometry–based PRIs reflect low physiologic total testosterone concentrations expected in female individuals after birth, PRIs established by some clinical analyzers report female total testosterone concentrations approximately 8 times higher, suggesting that the use of accurate methodologies is central to establishing appropriate PRIs. Literature search terms included, but were not limited to, pediatric reference intervals and/or children or pediatric in combination with the analytes listed below.
