[Total thyroxine (T4) and free thyroxine (FT4) in hypothyroidism and nonthyroid diseases of dogs]

In 1548 dogs total and free thyroxine were determined. 559 of these dogs had been divided into 13 groups: 130 were healthy dogs, 22 suffered from hypothyroidism, two from hyperthyroidism, 405 from various other internal diseases. The other 989 dogs did not belong to one of the groups of interest or could not be attached to a certain group. In all hypothyroid dogs FT4-values were hypothyroid, whereas T4 was hypothyroid just in 16 cases; the other six values were located in the "gray area", which is supposed to be 1.2 to 1.8 micrograms/dl (15 to 23 nmol/l). Many dogs with other diseases expressed low T4- and/or FT4-values, too. Low hormone values could be measured especially in case of severe diseases. If the clinical symptoms corresponded to hypothyroidism and both T4 and FT4 were situated in the hypothyroid area, hypothyroidism is generally assumed. In all the other cases further diagnostic procedures must be performed.