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Comparison of the average percentage of thyroid colloid and selected serum thyroid analyses in healthy euthyroid and severely ill dogs
Author(s) -
Torres S. M. F.,
Feeney D. A.,
Lekcharoensuk C.,
Fletcher T. F.,
Clarkson C. E.,
Nash N. L.,
Hayden D. W.
Publication year - 2002
Publication title -
veterinary dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.744
H-Index - 60
eISSN - 1365-3164
pISSN - 0959-4493
DOI - 10.1046/j.1365-3164.2002.00298_19.x
Subject(s) - euthyroid , medicine , thyroid , hormone , colloid , reference range , thyroid hormones , gastroenterology , endocrinology , physiology , chemistry
The diagnosis of canine hypothyroidism is not straightforward because the results of thyroid tests can be influenced by severe illness and medications. The need to find diagnostic tests that are not affected by these factors is urgent. The objectives of this investigation can be summarized as follows: (1) to establish a reference range for percentage colloid from healthy euthyroid dogs; (2) to compare the mean percentage colloid of the healthy dogs with that of severely ill dogs; (3) to define a group of ill‐euthyroid dogs based on the percentage colloid and evaluate their serum concentrations of total thyroxine (TT4), free thyroxine by equilibrium dialyses (fT4d) and endogenous TSH (eTSH); and (4) to determine if the mean percentage colloid correlates with the serum concentrations of TT4, fT4d and eTSH. Sixty‐one healthy‐euthyroid dogs and 66 severely ill dogs were included on the study. Thyroid glands were removed immediately after death. Morphometric analyses were performed on each thyroid lobe to determine the percentage colloid. Serum hormone concentrations were analyzed using commercially available tests validated at our laboratory. Descriptive statistics were used to report the results of the average percentage colloid and hormone concentrations. Unpaired Student’s t ‐test was applied to compare the percentage colloid between the group of healthy‐euthyroid dogs and the groups of sick dogs. Spearman’s rank correlation coefficient method was used to determine the correlation between each of the measured thyroid hormone values and the percentage colloid. The statistical analyses were carried out using Statistical Analysis System (SAS) software. A P‐ value of < 0.05 was considered statistically significant. No statistically significant difference was observed in mean percentage colloid between the groups of severely ill and healthy‐euthyroid dogs. Serum TT4 and fT4d concentrations were below the reference range in 57.6 and 31.8% of severely ill dogs, respectively. Only 6.1% of severely ill dogs had increased eTSH concentrations. No clinically significant correlation was found between serum thyroid hormones and percentage colloid. In conclusion, serum TT4 and fT4d concentrations were more frequently altered by severe illness than eTSH in dogs with percentage thyroid colloid equivalent to normal dogs. Serum thyroid hormones did not have a direct correlation with percentage colloid.