48
Hypothyroidism—a decreased TT
4
is consistent with but not necessarily definitively diagnostic of
hypothyroidism. Naturally occurring hypothyroidism is a common endocrine disorder in dogs and
rare in cats. Hypothyroidism can be seen in horses as well.
Nonthyroidal illness (NTI)—nonthyroidal illness can affect TT
4
levels (and potentially other thyroid
tests as well). Nonthyroidal illness can lower TT
4
levels, potentially into the hypothyroid range. The
more severe the nonthyroidal illness, the greater the potential impact on TT
4
levels.
Sample Type and Precautions
For use with serum, plasma, and whole blood (when using the Catalyst Whole Blood Separator).
Remove plasma or serum promptly from the cells or clot. If plasma is being collected, use only
lithium heparinized samples. Hemolyzed samples should not be used. Do not use fluoride/oxalate
as an anticoagulant.
Complementary Tests
Total T
4
should be evaluated in conjunction with a comprehensive history, physical examination,
CBC, complete biochemical profile, and urinalysis to provide a comprehensive database of
information in the diagnosis or suspicion of thyroid disease.
In dogs with low or low normal T
4
results and with consistent clinical signs, evaluate free T
4
(fT
4
) and
endogenous thyroid-stimulating hormone (TSH) and possibly thyroglobulin autoantibodies (TgAA)
to aid in confirming hypothyroidism.
Cats with consistent clinical signs and total T
4
(TT
4
) values in the borderline high range (gray zone)
may have early hyperthyroidism or a concurrent nonthyroidal illness (NTI). In these cases, consider
a free T
4
(fT
4
), a T
3
suppression test or radionuclide thyroid imaging to aid in confirming the
diagnosis.
Triglycerides (TRIG)
Triglycerides are usually present in the diet of dogs and cats, especially when the animals are
fed table scraps. They are also synthesized in the liver, mainly from carbohydrates, to provide a
secondary energy source and are stored in fatty tissue. Their hydrolysis to mono- and diglyceride
glycerol and free fatty acids is catalyzed by pancreatic lipase.
Principal Reason for Performing the Test
To detect abnormalities in lipid metabolism.
Most Common Abnormality Indicated by the Test
Increased triglycerides—High-fat diet or abnormalities in fat metabolism.
Sample Type and Precautions
Blood should not be drawn within 12 hours of a meal.
Remove plasma or serum promptly from the cells or clot. If plasma is collected, use only lithium
heparinized samples. Grossly lipemic specimens probably have very high triglycerides and should
be diluted before analysis.
Complementary Tests
Triglycerides should not be measured in isolation. If the sample is turbid or milky, the test should be
determined in conjunction with measurements of cholesterol and glucose, and hepatic and renal
function tests. Also consider repeat sampling if the patient has not been fasted for 12 hours.
Appendices
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