[The T index in the elderly with altered values of free thyroxine and/or thyrotropin. A new thyroid diagnostic-therapeutic index]

Routinary evaluation of FT4 and TSH, in elderly in-patients without thyroid disease shows frequent, isolated and, often unclear, changes from normal values of plasma TSH and FT4 concentrations. A new parameter called "T index" derived from the product of FT4 and TSH values has been used by the authors. In a previous work they studied "T index" variations in 1257 elderly subjects with normal FT4 and TSH levels. They have determined the "T index" theoretic model of distribution and identified a normality range (values from 5.78 to 50.76), a suspect range (values from 2.92 to 5.78 and from 50.76 to 68.6) and a pathologic range (values less than 2.92 and more than 68.6). Aim of this study was to investigate "T index" variations in a group of 357 elderly subjects with altered FT4 and/or TSH levels.

Patients were divided into eight groups according to different concentrations of FT4 and/or TSH levels. "T index" results were expressed as mean, standard deviation, maximum and minimum values. Patients were therefore divided into three groups (normality range, suspect range, pathologic range) according to "T index" distribution as previously described.

In 20% of elderly people hospitalized, we found alterations of thyroid hormones levels represented mostly by: a) FT4 normal; TSH low. b) FT4 normal; TSH high, c) FT4 low; TSH normal. In case of hypothalamus-hypophysis hypothyroidism and in case of hyperthyroidism, "T index" score is, usually, less than 2.92, whereas in case of hypothalamus-hypophysis hypothyroidism and hypothyroidism "T index" score is, nearly always, more than 68.6. When TSH levels are into the range of normality "T index" score has always normality levels. The "T index" helps us to divide patients with subclinical hyperthyroidism into two groups: one with values from 5.78 to 2.92 (suspect range), and the other, with values less than 2.92 pathologic range). In patients with subclinical hypothyroidism, some patients have values from 50.76 to 68.6 (suspect range), other patients have values more than 68.6 (pathologic range).

In case of subclinical hypothyroidism or subclinical hyperthyroidism the use of "T index" seems to be a good way to select the cases in which it is better to start pharmacological treatment (hormonal replacement or thyroid inhibition) from those which is better to follow-up.