Twenty-four hour variations of thyroid hormones and thyrotrophin concentrations in hypothyroid infants treated with L-thyroxine.
The 24 hour plasma profile of T4, FT4, T3 and TSH was measured in a group of infants treated for congenital hypothyroidism with an oral aqueous preparation of L-T4 (5-7.5 micrograms/kg) given as a single dose at 0800 h. Mean basal plasma T4 was 8.4 +/- 2.0 micrograms/dl (mean +/- SD) and remained constant during the study while mean serum FT4 increased significantly from 1.64 +/- 0.50 ng/dl to a maximum of 2.08 +/- 0.63 ng/dl 4 h after medication. Plasma T3 decreased significantly from 241 +/- 48 ng/dl to 202 +/- 36 ng/dl 6 h after drug administration. Finally, plasma TSH decreased significantly from a mean of 24.2 +/- 18.8 microU/ml to 14.8 +/- 10.5 microU/ml 6 h later. Therefore during treatment of congenital hypothyroidism with L-T4 no specific schedule for T4 sampling is required. However, TSH determination 4 to 8 h after medication could slightly underestimate mean levels. In addition, any attempt to monitor treatment by FT4 determination should take into consideration variations of plasma values in the hours following L-T4 absorption.
D002940:Circadian Rhythm; D003409:Congenital Hypothyroidism; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000188:drug therapy; D007223:Infant; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood / Q000627:therapeutic use*; D014284:Triiodothyronine / Q000097:blood
D013963:Thyroid Hormones; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine