Manufacturer’s reference intervals for free thyroxine are not ideal for children on thyroxine replacement therapy and target ranges need to be assay-specific

Elizabeth Wheeler, Kay Weng Choy, Lit Kim Chin, Wijeratne Nikila, McNeil Alan, Sue Matthews, James Doery, Zhong Lu, Philip Bergman, Tina Yen

Research output: Contribution to journalMeeting Abstract

Abstract

Objectives: We aimed to determine the physiologically correct free thyroxine (FT4) target range in children on thyroxine for primary hypothyroidism to guide optimal therapy for all children on thyroxine including those with central hypothyroidism. There are biases among current FT4 assays as reflected by the manufacturers' reference intervals. Therefore, we postulate that the ideal FT4 target range for children on thyroxine therapy would also be assay-specific.

Methods: Patients with primary hypothyroidism were prospectively recruited. Patient samples with thyroid-stimulating hormone (TSH) in the normal range (0.4-4.0 mIU/L) on Beckman Coulter DxI were included for analysis. Samples were measured on four other instruments (Siemens Centaur, Roche Cobas, Abbott Architect, Ortho Vitros). FT4 ranges (median (2.5th-97.5th)) were calculated. The results were compared to the manufacturers' quoted reference intervals (e.g. DxI: FT4, 7.9-14.4 pmol/L).
Results: Results from thirty-two patients aged from 2 to 18 years were analysed. In the thyroxine-treated group (congenital hypothyroidism (n=24) and autoimmune hypothyroidism (n=8)), FT4 was 14.3 pmol/L (11.5-17.3) on DxI, FT4 was 18.5 pmol/L on Centaur.
Conclusions: This study suggests that target FT4 in children on thyroxine should be well above the manufacturer's quoted reference interval. In thyroxine-treated hypothyroidism with normal TSH, FT4 levels vary as much as 30% among the different assays. Therefore, target FT4 ranges should also be assay-specific.
Original languageEnglish
Article numberP1-1701
Number of pages1
JournalHormone Research in Paediatrics
Volume88
Issue numberSupplement 1
Publication statusPublished - 30 Sep 2017
Externally publishedYes
Event10th International Meeting of Pediatric Endocrinology - Marriott Wardman Park, Washington , United States
Duration: 14 Sep 201717 Sep 2017
Conference number: 10

Keywords

  • paediatric
  • thyroid
  • thyroxine replacement
  • reference intervals

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    Wheeler, E., Choy, K. W., Chin, L. K., Nikila, W., Alan, M., Matthews, S., Doery, J., Lu, Z., Bergman, P., & Yen, T. (2017). Manufacturer’s reference intervals for free thyroxine are not ideal for children on thyroxine replacement therapy and target ranges need to be assay-specific. Hormone Research in Paediatrics, 88(Supplement 1), [P1-1701].