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Thyroxine, Free (fT4) Human ELISA

  • Regulatory status:RUO
  • Type:Competitive ELISA, Immobilized antigen
  • Species:Human
Cat. No. Size Price

RCD015R 96 wells (1 kit) $369,69
PubMed Product Details
Technical Data


Competitive ELISA, Immobilized antigen



Sample Requirements

25 µl/well


At ambient temperature. Upon receipt, store the product at the temperature recommended below.


Store the complete kit at 2–8°C. Under these conditions, the kit is stable until the expiration date (see label on the box).

Calibration Curve

Calibration Range

2–95 pg/ml

Limit of Detection

1 pg/ml


Research topic



Thyroxine (T4), the principal thyroid hormone, circulates in blood almost completely bound to carrier proteins. However, only the free (unbound) fraction of thyroxine is considered to be biologically active. The main carriers of thyroxine are thyroxine-binding globulin (TBG), pre-albumin and albumin. The measurement of free thyroxine (fT4) levels correlate better with the clinical status than total thyroxine levels.
The free T4 assay is a one-step competitive ELISA system that is rapid and easy to perform compared to equilibrium dialysis and ultrafiltration methods, which are cumbersome and time-consuming. This system employs a highly specific monoclonal antibody and a non-analog tracer that was proved experimentally to have no significant binding to TBG and albumin.
In the euthyroid, normal population the free T4 concentration is 7 – 22 pg/ml. The level of free T4 is decreased in hypothyroidism while in thyrotoxic patients the level of free T4 is increased. This assay is used at times with other thyroid tests for in vitro diagnostic purposes and for assessing patients who are receiving thyroid treatments (follow-up).

Summary References (8)

References to Thyroxine

  • Comoglio S, Celada F. An immuno-enzymatic assay of cortisol using E. coli beta-galactosidase as label. J Immunol Methods. 1976 Mar;10 (2-3):161-70
  • Ingbar SH, Braverman LE, Dawber NA, Lee GY. A new method for measuring the free thyroid hormone in human serum and an analysis of the factors that influence its concentration. J Clin Invest. 1965 Oct;44 (10):1679-89
  • McComb RB, Bowers GN, Posen S. Alkaline Phosphatase. Plenum Press, New York. 1979;1st Ed., Chap. 9:525-704
  • Robbins J. Radioassay and the thyroid gland. Metabolism. 1973 Aug;22 (8):1021-6
  • Schall RF Jr, Fraser AS, Hansen HW, Kern CW, Tenoso HJ. A sensitive manual enzyme immunoassay for thyroxine. Clin Chem. 1978 Oct;24 (10):1801-4
  • Selenkow HA, Robin NI. The diagnosis and management of common thyroid diseases. J Maine Med Assoc. 1970 Oct;61 (10):199-211 passim
  • Sterling K, Hegedus A. Measurement of free thyroxine concentration in human serum. J Clin Invest. 1962 May;41:1031-40
  • Surks MI, Squef R, Oppenheimer JH, Hauer H. Binding of Thyroxine by serum proteins evaluated by equilibrum dialysis and electrophoretic techniques. Alterations in nonthyroidal illness. J Clin Invest.. 1963 Nov; 42 :1769-82
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