Response to Letter to the Editor: "Changes in Thyroid Function Across Adolescence: A Longitudinal Study"

Abstract

We thank Dr. Raverot and colleagues for their comments, which highlight the challenges and complexities of establishing appropriate reference intervals. With regard to assay performance, inter-assay coefficients of variation in our study were as follows: TSH, 3.3% and 3.2% at 0.37 and 4.3 mU/L respectively; FT4, 4.8% and 5.9% at 10 and 28 pmol/L, respectively; and FT3, 4.8% and 3.4% at 3.7 and 9.9 pmol/L, respectively. We confirm that the study was performed before the change from 2-point to 6-point calibration for FT3. We are aware of the data regarding biological variation in TSH, FT4, and FT3, but these would not account for the longitudinal trends and sex difference in FT3 shown in Figure 3 of the paper, nor is it relevant to determining reference intervals.