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Triiodothyronine, Free (fT3) Human ELISA

  • Regulatory status:RUO
  • Type:Competitive ELISA, Immobilized antigen
  • Other names:T3
  • Species:Human
Cat. No. Size Price

RCD014R 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

1–40 pg/ml

Limit of Detection

0.3 pg/ml


Research topic



Triiodothyronine (T3) is a thyroid hormone found circulating in the bloodstream. T3 contains three iodine atoms and is produced largely through the extrathyroidal conversion of thyroxine (T4), the principal thyroid hormone with four iodine atoms. Most of the T3 that circulates in the blood is bound to carrier proteins such as TBG, pre-albumin and albumin. The free fraction of T3 (fT3), which represents only 0.25% of the total amount, is considered to be the physiological active fraction.
Total T3 levels depend not only on thyroid status and the peripheral conversion of T4 to T3, but also on the concentration of thyroid hormone-binding proteins. Free T3 (fT3) on the other hand, is largely unaffected by variations in these carrier proteins which can occur under conditions such as pregnancy, estrogen therapy and the use of oral contraceptives. Therefore, free T3 typically reflects a patient’s actual thyroid status more reliably than total T3.
Measurement of free T3 is generally recommended for patients with symptoms of hyperthyroidism as found in Graves' disease, toxic adenoma and toxic multinodular goiter.

Summary References (14)

References to Triiodothyronine

  • Bergmann PJ, Van Tricht L. Free triiodothyronine in hypothyroidism and in nonthyroidal illness. Clin Chem. 1994 Mar;40 (3):496-7
  • Chopra IJ. RIA of iodothyronines. In: Abraham GE eds. Handbook of radioimmunoassay. New York: Marcel Dekker Inc,. 1997:679;
  • Cohen JH 3rd, Ingbar SH, Braverman LE. Thyrotoxicosis due to ingestion of excess thyroid hormone. Endocr Rev. 1989 May;10 (2):113-24
  • Demers LM. Thyroid function testing and automation. J.Clin. Ligand Assay. 1999;22:38;
  • Ekins R. Measurement of free hormones in blood. Endocr Rev. 1990 Feb;11 (1):5-46
  • 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
  • John R, Henley R, Shankland D. Concentrations of free thyroxin and free triiodothyronine in serum of patients with thyroxin- and triiodothyronine-binding autoantibodies. Clin Chem. 1990 Mar;36 (3):470-3
  • Kalra J, Hart IR. Value of free thyroxine (FT4), free triiodothyronine (FT3), and sensitive thyrotropin (TSH) assay in the assessment of optimal thyroxine therapy. Clin Biochem. 1987 Aug;20 (4):265-7
  • Mullinger RN, Gates J. Free triiodothyronine in nonthyroidal illness. Clin Chem. 1993 Jul;39 (7):1555
  • Nauman JA, Nauman A, Werner SC. Total and free triiodothyronine in human serum. J Clin Invest. 1967 Aug;46 (8):1346-55
  • Oddie TH, Fisher DA, Dussault JH, Thompson CS. Triiodothyronine turnover in euthyroid subjects. J Clin Endocrinol Metab. 1971 Oct;33 (4):653-60
  • Pedersen KO. Simultaneous determination of the free thyroxine and triiodothyronine fractions in serum. Scand J Clin Lab Invest. 1974 Nov;34 (3):241-6
  • Weeke J, Orskov H. Ultrasensitive radioimmunoassay for direct determination of free triiodothyronine concentration in serum. Scand J Clin Lab Invest. 1975 May;35 (3):237-44
  • Wilkins TA, Midgley JE, Stevens RA, Caughey I, Barron N. Assay performance and tracer properties for two analog-based assays of free triiodothyronine. Clin Chem. 1986 Mar;32 (3):465-9
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