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VT30: Total T4 Immunoassay

The hormone thyroxine, also known as T4 (3, 5, 3', 5', tetraiodothyronine), is produced by the iodination of tyrosyl residues on the thyroglobulin protein in the thyroid gland. The cleavage and release of T4 (as well as triiodothyronine, T3) from thyroglobulin is stimulated by the peptide hormone thyroid stimulating hormone (TSH). Nascent T4 is quickly bound to the plasma proteins thyroxine binding globulin (TBG), thyroxine binding pre-albumin (TBPA), or albumin.  A small percentage of the total T4 is also found free (not protein bound) in the serum.   The primary role of T4 is the regulation of metabolism. Serum levels of total T4 correlate with the rates of T4 secretion and metabolism, and is a reliable tool for the diagnosis and management of thyroid disease. 

Most total T4 assays are designed for human levels of T4 and lack the sensitivity required for companion animal use.  Assays designed for veterinary use typically require radioisotopes to attain sufficient sensitivity.  Our assay is a competitive ELISA with significantly improved sensitivity without relying on radioactivity. 

It has been optimized for use with canine, feline, and equine samples.  An ultrasensitive Total T4 assay is also available for use with birds and reptiles.

Total T4 Normal Reference Ranges

Species nmol/L µg/dL
Canine 20.0 - 60.0 1.55 – 4.65
Feline 19.35 – 51.60 1.48 – 4.50
Equine 19.35 – 58.05 1.50 - 4.50

VT 30 Curve