Parallel Determination of Total Thyroxine and Thyrotropin Concentrations in Diagnosis of Primary Hypothyroidism in the Dog

Abstract

The objective of the work was to verify the validity of parallel determination of total thyroxine (tT 4 ) and thyrotropin (cTSH) concentrations in the diagnosis of primary hypothyroidism in the dog. The concentrations of total thyroxine and thyrotropin were determined by chemiluminiscence immunoassay in the serum of a total of 117 dogs: 40 negative controls, 66 dogs with euthyroid sick syndrome and 11 patients with primary hypothyroidism. The average tT 4 concentration in the group of healthy dogs was 25.8 ± 5.48 nmol/l and the average cTSH concentration was 0.17 ± 0.13 ng/ml. In the group of patients with primary hypothyroidism the tT 4 concentrations were significantly decreased in 10 out of 11 cases (10.12 ± 2.01 nmol/l), while the cTSH concentrations were significantly increased (2.9 ± 2.04 ng/ml). In one patient with primary hypothyroidism, only the tT 4 concentration was decreased to 9.0 nmol/l, but the cTSH concentration was found to be within the reference range (0.04 ng/ml). The average tT 4 concentration in the group of patients with euthyroid sick syndrome was 11.7 ± 3.16 nmol/l, while the average cTSH concentration in the same group of patients was 0.14 ± 0.12 ng/ml. The concentrations of the two hormones mentioned above were compared between the different groups using the non-parametric Mann-Whitney test. The concentration of tT4 was significantly higher (p < 0.01) in the group of healthy dogs compared to the dogs with primary hypothyroidism and the dogs with euthyroid sick syndrome. The concentration of cTSH was significantly higher ( p < 0.01) in the dogs with primary hypothyroidism compared to the healthy dogs and the dogs with euthyroid sick syndrome. The results of this work show that parallel determination of tT 4 and cTSH represents a highly sensitive and specific method which is suitable for differentiating between primary hypothyroidism and other diseases that significantly reduce tT 4 concentrations. Canine TSH, tT 4 , euthyroid sick syndrome