Objective—To determine whether nonthyroidal disease
of various causes and severity is associated with
abnormalities in baseline serum concentrations of
total thyroxine (T4), triiodothyronine (T3), free T4, or
thyrotropin (thyroid-stimulating hormone [TSH]) in
dogs believed to be euthyroid.
Animals—223 dogs with confirmed nonthyroidal diseases
and presumptive normal thyroid function, and
150 clinically normal dogs.
Procedure—Serum total T4, total T3, free T4, and TSH
concentrations were measured in dogs with confirmed
nonthyroidal disease. Reference ranges for
hormone concentrations were established on the
basis of results from 150 clinically normal dogs.
Results—In dogs with nonthyroidal disease, median
serum concentrations of total T4, total T3, and free T4
were significantly lower than those in clinically normal
dogs. Median serum TSH concentration in sick dogs
was significantly greater than that of clinically normal
dogs. When stratified by severity of disease (ie, mild,
moderate, and severe), dogs with severe disease had
low serum concentrations of total T4, total T3, or free
T4 more commonly than did dogs with mild disease.
In contrast, serum TSH concentrations were more
likely to remain within the reference range regardless
of severity of disease.
Conclusions and Clinical Relevance—Results indicate
that serum total T4, free T4, and total T3 concentrations
may be low (ie, in the hypothyroid range) in
dogs with moderate to severe nonthyroidal disease.
Serum TSH concentrations are more likely to remain
within the reference range in sick dogs. (J Am Vet
Med Assoc 2001;219:765–769)