Analysis of Overall Pathophysiological Relationships between Serum Levels of TSH and Thyroid Hormones Using a Large Laboratory Database

Abstract

Factors associated with the basal level of serum thyrotropin (TSH) were analyzed over a wide range of pathophysiological conditions by means of a large laboratory database on thyroid function. When data were analyzed two-dimensionally, serum TSH showed significant inverse correlations with total triiodothyronine (T₃), free T₃ index (FT₃I), total thyroxin (TT₄) and free T₄ index (FT₄I) in the order of increasing intensity. The three-dimensional analysis, however, revealed that 1) total hormone levels were actually unrelated to serum TSH when the levels of free hormone indices were held constant, 2) the relation between FT₃I and TSH became obscure when the influence of FT4I was similary removed. On the other hand, 3) the relation of FT₄I with TSH was unaffected by the level of FT₃I.
These results suggest that free T₄ is the main determinant of the serum TSH level. This study also implies that it is possible to use large amounts of laboratory data to elucidate the overall profile of a given patho-physiological system, whose structure is only partially revealed by conventional clinical or animal studies.