Intra-individual and seasonal variations of thyroid function tests in healthy subjects
Nishi, I.; Ichihara, K.; Takeoka, K.; Miyai, K.; Amino, N.
Rinsho Byori. Japanese Journal of Clinical Pathology 44(2): 159-162
1996
ISSN/ISBN: 0047-1860 PMID: 8851200 Document Number: 466196
We report intra-individual and seasonal variations of thyroid function tests in healthy subjects. Blood samples were obtained from thirteen healthy males and seven healthy females every two weeks over a period of one year, and totally 25 samplings of each were made. Serum thyrotropin (TSH), free thyroxine (FT4) and free triiodothyronine (FT3) were measured after the completion of the sampling. The 25 samples from each subject were always assayed with the same assay run. Variations of FT4 and FT3 in each subject were narrow and approximately one-third of normal reference ranges. The magnitude of individual variation of TSH values was proportional to the average of TSH in each individual. Serum TSH and FT3 values during winter were significantly higher than those during summer, but such change was not observed on serum FT4.