[Management of primary hypothyroidism in childhood treated with thyroid extract (author's transl)]. / Surveillance biologique des hypothyroïdies primitives de l'enfant sous traitement par extraits thyroïdiens.

In a group of 19 children with primary hypothyroidism who were treated with thyroid extract, linear relationships were found between blood thyroxine and triiodothyronine levels and the dose of thyroid extract adjusted for surface area. Thus it is likely that the composition of thyroid extract is homogeneous and that the metabolism of thyroid hormones in the patients is similar. Thyroxine (T4) was the most reliable parameter for monitoring treatment as T3 levels were elevated in patients who were otherwise euthyroid. T3 uptake was rather insensitive but the free thyroxine index agreed well with the T4 level. A negative linear semilogarithmic correlation was demonstrated between TSH and T4 but not with T3. In some cases TSH was still raised although the T4 had returned to normal. It is postulated that this could be due to thyrotropic cells hyperplasia. TRH tests did not provide any further information. The recommended dose of thyroid extract which is needed to raise the T4 above the lower limit of normal for age (-2 SD) can be calculated from the regression of T4 and dose of thyroid extract. The mean value was 8.49 +/- 0.86 cg/m2.