Total T4 assay

Total T4 is a measure of all T4 in the circulation and includes protein-bound and free T4. Total T4 may be measured by radioimmunoassay (RIA) or enzyme immunoassay. Gribbles Veterinary Pathology offers an automated enzyme immunoassay for testing Total T4. Both of these tests are validated for use in dogs and cats, and studies show an excellent correlation between these two test methodologies. Furthermore, the enzyme immunoassay has been shown to be less sensitive to interference from autoantibodies. Total T4 by enzyme immunoassay is precise, reliable and should be used as a baseline determination of thyroid status in dogs and cats. As with all endocrine disease, diagnosis may be complicated by concurrent disease and use of medications, including certain antibiotics, corticosteroids and anticonvulsants. As Total T4 predominantly measures protein-bound thyroid hormone, serum concentration may be affected by conditions that impact on the patient’s serum proteins. Interpretation of results should always take clinical history into account and may be aided by combining Total T4 with Free T4 and canine TSH as appropriate.

See also “Diagnosis and monitoring of hypothyroidism” and “Diagnosis and monitoring of hyperthyroidism”.


Canine, feline, equine




Plain (red top) or gel (serum separator) tube

Collection protocol:

Standard venepuncture