Study on the TRH test during the course of the treatment of primary hypothyroidism

Abstract

Twenty-seven patients with primary hypothyroidism (males 8, females 19, aged 18-80 years old) were treated by thyroid hormone medication for replacement therapy and then TRH test was performed in total on 97 occasions. The patients were divided into three groups by the medication used : the L-thyroxine (L-T4) group in doses of 50-450 μg/day (0.89-3.41 μg/kg/day), the L-triiodothyronine (L-T3) group in doses of 15-75 μg/day (0.37-1.39 μg/kg/day), and the L-T4 + L-T3 (10 : 1) group in doses of 50-50 μg/day (0.80-3.0 μg/kg/day) of L-T4 in combination with 5-15 μg/day (0.08-0.30μg/kg/day) of L-T3. The TRH test was performed for each case except 4 cases of the L-T3 group at small dose (0.37-0.56 μg/kg/day), more than one month following the change of medication, and the peak values of serum TSH measured after TRH injection were compared with serum basal TSH, T4, T3, RT3U, total cholesterol measured before TRH injection, and the doses of thyroid hormone medication.
The results obtained are as follows :
I. The results common to all groups.
1) There was marked difference in basal TSH among the cases even if they showed the range of normal values of serum T4 and T3 or serum T3 alone (L-T3 group). And these cases showed various types of response, from no-response to hyper-response to the TRH.
2) When basal TSH values were high, all cases were hyper-responsive to TRH administration.
3) Except the L-T3 group, some cases were hyper-responsive to the TRH even if they showed normal values of basal TSH.
4) There was almost no correlation between the RT3U and the peak TSH values, especially in the L-T3 group.
5) There was no correlation between the serum total cholesterol and the peak TSH values.
6) There was negative correlation between the doses of thyroid hormone medication and the peak TSH values, in the order of the L-T3 group L-T4 group L-T4 + L-T3 group.
II. The results on the L-T4 group.
1) The serum T4 was within the normal range in 92.9% of the cases, and these values were significantly correlated with each of the medication dose, basal TSH, peak TSH, and serum T3.
2) The serum T3 was within the normal range in 88.1% of the cases, and these values were not correlated with the dose of L-T4, but correlated with each of the basal TSH, peak TSH and serum T4.
3) The cases which showed hyper-response to the TRH were with not more than 2.12 μg/kg/day in the dose of L-T4, with 11.6 μg/100ml in serum T4 and with more than 102 μg/ 100ml in serum T3.
4) The cases which showed normal serum T4 and serum T3 lower than normal showed normal-response or hyper-response to the TRH.
5) Nineteen cases which showed normal-response to the TRH were with 1.18-3.13 (2.20±0.47) μg/kg/day in the doses of L-T4, with 4.9-13.6 (10.0±2.16) μg/ml in serum T4, and with 65-472 (96±25.7) μg/100ml in serum T3.
III. The results on the L-T4 + L-T3 group.
1) The serum T4 was within the normal range in 87.2% of the cases, and there were some cases which were lower in serum T4 when the dose of L-T4 was comparatively large, 2.44 μg/kg/day, showed hyper-response to the TRH.
2) The serum T3 was within the normal range in 97.4% of the cases and the values were not correlated with any of the medication dose, basal TSH, and peak TSH values.
3) No cases showed hyper-response to the TRH when serum T3 were more than 147 μg/ 100ml.
4) Twelve cases which showed normal-response to the TRH were with 106.2+20.2 μg/ day (2.06±0.50 μg/kg/day) in the dose of L-T4, with 5.8-11.0 (9.1±1.78) μg/100ml in serum T4 and with 65-170 (112±35.5) μg/ 100ml in serum T3.
IV. The results on the L-T3 group.
1) The serum T3 was within the normal range with the small dose of L-T3 of 15 μg/day (0.37 μg/kg/day).