Free Triiodothyronine ELISA Kit (Free T3)


Human free triiodothyronine ELISA kit is a reliable quantitative procedure to measure free T3 (free triiodothyronine, FT3) levels in human serum. The detection sensitivity limit of this assay is 0.536 pg/ml.


The biologically active form of free triiodothyronine (free T3, FT3) is only represented by a small fraction (approx. 0.3%). This is the circulating hormone that is unbound (free) from any carrier proteins such as thyroxine-binding globulin (TBG).  In many clinical conditions it has been found that the concentrations of carrier proteins present can be altered, for example; during pregnancy, oestrogen therapy and oral contraceptives. As the levels of carrier proteins change so does the amount of total T3 present, however, the free T3 (FT3) concentrations remain constant. For this reason alone, measuring free T3 levels correlates more reliably with clinical status in comparison to total triiodothyronine concentrations.


All reagents supplied need to be stored at 2 °C – 8 °C, unopened reagents will retain reactivity until expiration date. Do not use reagents beyond this date.

  • Microtiterwell Plate: Break apart strips which have been coated with anti T3 antigen.
  • Standard 0-5: Concentrations: 0, 1.0, 2.5, 5.9, 10.0, 20.0 pg/ml, made from triiodothyronine.
  • Control Low and Control High: Containing human triiodothyronine antibody.
  • Enzyme Conjugate: Consisting of anti-triiodothyronine conjugated with horseradish peroxidase.
  • Substrate Solution: Tetramethylbenzidine (TMB).
  • Stop Solution: 0.5 M H2SO4. Avoid contact with the stop solution. It may cause skin irritations and burns.
  • Wash Solution (40x Concentrated).


The minimum sensitivity detection limit of human free triiodothyronine (free T3, FT3) using current free T3 ELISA kit is 0.536 pg/ml. The dynamic assay range for this kit is 1.0 – 20.0 pg/ml.


– Assay Dynamic Range: 0.38 – 20.0 pg/ml
– Specificity (Cross Reactivity): L-Thyroxine, L-Tyrosine, 3-Iodo-L-tyrosine, Furosemide, Sodium Acetylsalicylate (< 0.001%), 3.5-Diiodotyrosine (0.0012%).
– Sensitivity: LoB (0.3270 pg/ml), LoD (0.536 pg/ml), LoQ (0.990 pg/ml)
– Intra-Assay Variation: 1.2 – 9.1%
– Inter-Assay Variation: 7.4 – 12.0%
– Inter-Lot Variation: 8.6 – 11.3%
– Recovery: 96.4 – 106.6%
– Interfering Substances: None
– High-Dose-Hook Effect: No hook effected observed.


  1. Scand. J. Clin. Lab Invest (1974) 34, 247. Pederson, K.O.
  2. Immunoassay Handbook, Stockton Press, (1994) 339. Wild, D.
  3. Metabolism (1981) 30, 717. Wenzel, K.W.
  4. Clin Chem (1983) 29, 1324. Bhagat,C. et al.
  5. Clin Chem (1982) 28, 1241. Lundberg, P.R. et al.
  6. J Clin Endocrinol Metab (1982) 54, 300. Melmed, S. et al.
  7. Clin Endocrinol (1983) 18, 11. Lalloz M.R. et al.


  • Full Name: Free Triiodothyronine ELISA Kit (Free T3)
  • Reactivity: Human
  • Sample Type: Serum
  • Sensitivity: 0.536 pg/ml



Online Enquiry Form

"*" indicates required fields

Please check mark information required:


Your secretory IgA ELISA gave good results and I was also really impressed with how quickly we received it.

L. Johnston
PhD Student / University of Glasgow

It is refreshing to know that you have a technical team that is very knowledgeable. I have already recommended your company to other researchers in our department.

Dr. P. Anderson
Lecturer / University College London (UCL)

I am a first time user and found that your instruction manual was very easy to follow. The insulin ELISA assay performed well and I was happy with the results that were generated.

J. Thomas
Senior Technician / Addenbrooke’s Hospital

I carried out a pilot study comparing the performance of many ELISA assay's from different suppliers and found your kits to be one of the better performers. We observed good linearity and tight replicates.

Dr. C. Davies
Lead Scientists / AstraZeneca

You are my first point of contact when I am looking to purchase ELISA. You have such an easy and simple system, yet it is very effective.

A. Shaw
Purchasing / University of Oxford