Free Thyroxine (FT4) ELISA Kit

  • Created on the 2 February, 2017.


L-Thyroxine (T4) has a primary influence on oxygen consumption and protein synthesis in virtually every tissue, it is also the most commonly analysed thyroid hormone during the diagnostics of thyroid function. Other functions of T4 include growth, development and sexual maturation. Most of the serum T4 is bound to transporter proteins (thyroxine binding globulin, thyroxine binding pre-albumin and albumin). Only a small portion approx. 0.03% exists as the active unbound (free) form which is responsible for exerting its effect on cells.

During the earlier thyroid function test procedures, the variable effect of thyroxine binding globulin (TBG) was overcome by calculating the free thyroxine index (FTI). The FTI is the product of thyroid uptake (TU) and total T4 concentration and was used to assess the number of TBG binding sites that were available. This was quite time consuming protocol and required two assays to be performed (TU and total T4), but it did provide a better thyroid status level compared to total T4 alone. The current free T4 ELISA kit method is intended to determine the clinical status of the thyroid following a single assay analysis and it also directly reflects equilibrium exist in serum between TGB-bound T4 and T4. The determination of free T4 levels is considered to be a good indicator of patient thyroid status.


Free T4 ELISA kit is a reliable quantitative procedure to measure free thyroxine (FT4) concentrations in human serum. The sensitivity detection limit of this assay is 0.5 ng/dl.


Based on 95 % confidence limit the lowest detection concentration of free thyroxine (FT4) that can be distinguished using this free thyroxine ELISA kit from the standard 0 was 0.5 ng/dl.


  1. J. Biological Chemistry (1948) 173, 175. Barker, S.B.
  2. J. Clinical Endocrinol. (1971) 33, 865. Chopra, I.J., Solomon, D.H. and Ho, R.S.
  3. Clinical Chemistry (1975) 21, 3660. Young, D.S., Pestaner, L.C. and Gilberman, U.
  4. Diagnosis and Treatment of Thyroid Disease, Cleveland CRC Press (1975) p. 19-51. Sterling, L.


  • Full Name: Free Thyroxine (FT4) ELISA Kit
  • Reactivity: Human
  • Sample Type: Serum
  • Sensitivity:  0.5 ng/dl



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