Pediatric reference intervals for SHBG using the Roche Cobas e411 and e601 methods have been reported previously , , though our results can only be superficially compared because of differences in biochemical and statistical analysis. In this sense, we make the assumption that if the reference intervals are determined with the same albumin estimates as the patient, then results will be interpretable, though not applicable to other analytical methodologies. This study has also not taken into account the fact that median albumin concentrations by age are not fixed at 43 g/L throughout life, but show age-dependence, being lower in early childhood–especially in the neonatal period and in children under 4 years .
As iron has been shown to also be higher in males, but transferrin has no apparent sex difference, the transferrin saturation sex difference is most likely a result of higher iron levels in males (4). Age- and sex-specific scatter plot of percent transferrin saturation in the CALIPER pediatric population Data were analyzed in accordance with Clinical and Laboratory Standards Institute (CLSI) EP28-A3c guidelines on defining, establishing, and verifying reference intervals in the clinical laboratory (12). Unfortunately, in many cases pediatric laboratory test results are interpreted based on reference intervals established from an adult reference population. The percentage of these iron binding sites occupied by iron is defined as the transferrin saturation. Though it not possible to implement fully continuous age-dependent reference intervals into a laboratory information system, point estimates naturally permit reference interval estimates that are as granular as month-by-month or year-by-year.
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.
This method is resistant to outliers and makes no assumptions about symmetry, normality, linearity, and heteroscedasticity. Total CVs were observed to be 1.4–2.1% for concentrations ranging from 24.0–129 nmol/L. The assay total coefficient of variation (CV) ranges from 4.2–6.8% for concentrations of 0.14–21.76 nmol/L. The calibration range of the assay is 0.05–45.0 nmol/L and traceable to the National Institute of Standards (NIST) SRM 971 "Hormones in Frozen Human Serum" standard reference material. After vortexing for 3 min, samples were centrifuged in plate for 10 min at 3000 rpm (948 g). T analysis was performed using a modification of French’s method , as previously described .
Therefore, the third second of compression is the ideal time to record a skinfold thickness measurement(16–19). During the first two seconds of compression, the tissue fibres are reoriented in the initial phase (0⋅0 to 0⋅5 s) followed by stretching of the elastic components (0⋅5 to 2⋅0 s) and a brief exponential decrease in the thickness skinfold. The dynamic and static characteristics of a skinfold in response to external compression are determined by the composition, viscosity and elasticity of the skin and subcutaneous adipose tissue at each anatomical site. The static calibration upward(4) and downward(7) by pressure of the jaws was determined in experiments with rudimentary methods and important limitations. The 10 mm pinion is the shaft that connects two 30 mm sprockets and interacts with the scaled indicator dial with 1⋅0 mm resolution in the range of 0 to 60 mm.
A few years later, a new and different skinfold caliper was introduced in 1961. In 1953, James Tanner (1920–2010) described the first precision anthropometric instrument designed to directly and specifically measure the compressed thickness of subcutaneous adipose tissue plus the skin called the skinfold caliper(4). Therefore, a new downward static calibration test and the first eligibility flowchart for a skinfold caliper have been proposed. Choosing a type of skinfold caliper for regular use, without conflict of commercial interest, requires a critical understanding of the physical, mechanical and functional characteristics that configure it. The area of the jaws, the coefficient of spring and the static and dynamic downward pressure of each type of skinfold caliper must be determined in the metrological laboratory and added to the technical user manual. Our report suggests that commercially available technical specifications are insufficient to judiciously choose a skinfold caliper. It is well established that the physical, mechanical and functional specificity of each type of skinfold caliper makes its interchangeable use impossible.
Transferrin saturation required 3 separate age partitions, with an additional sex partition for 14- Transferrin saturation was subsequently calculated and statistically relevant age- and sex-partitions were determined. Reference intervals are an essential tool against which to evaluate results of individual patients for clinical decision-making.