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.
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 language | English |
|---|---|
| Article number | P1-1701 |
| Number of pages | 1 |
| Journal | Hormone Research in Paediatrics |
| Volume | 88 |
| Issue number | Supplement 1 |
| Publication status | Published - 30 Sept 2017 |
| Externally published | Yes |
| Event | 10th International Meeting of Pediatric Endocrinology - Marriott Wardman Park, Washington , United States Duration: 14 Sept 2017 → 17 Sept 2017 Conference number: 10 |
Keywords
- paediatric
- thyroid
- thyroxine replacement
- reference intervals