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IMMUNOgen - Immunoassays Plasma,Serum Free T4 Tests per Package: 100
IMMUNOgen The Eclectica Free T4 assay for the Eclectica and Eclectica TiCA analysers has been designed for the quantitative determination of free thyroxine (Free T4) in human serum and heparinized plasma. The method can be used to measure free thyroxine concentrations over the range of 0.4 to 100 pg/ml (0.51 to 129 pmol/l). Code: 1708500 Package: 2 x 50
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  • 5 Kits
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  • Stock:
  • Available
    *Usually shipping within 5 business days
  • Min Order:
  • 5 Kits
  • Shipping:
  • Not Included

For Quantity Orders: Request a Quote

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The Eclectica Free T4 assay for the Eclectica analyzers has been designed for the quantitative determination of free thyroxine (Free T4) in human serum and heparinized plasma. The method can be used to measure free thyroxine concentrations over the range of 0.4 to 100 pg/ml (0.51 to 129 pmol/l).

Thyroxine or 3, 5, 3', 5', -tetraiodo-L-thyronine (T4) is a thyroid hormone with a molecular weight of 777 daltons, synthesized in the thyroid gland by iodination of tyrosine bound to the specific protein thyroglobulin (1). As part of the thyroglobulin molecule, T4 is stored in the follicles of the thyroid gland. When T4 is needed, the thyroglobulin is hydrolyzed and T4 is released into the bloodstream (2).

In serum, T4 exists in a reversible equilibrium between two states; bound and free. T4 bound to serum binding proteins, primarily thyroxine binding globulin (TBG), and to a lesser degree thyroxine binding prealbumin (TBPA) and albumin represents greater than 99.97% of the total thyroxine (3). However, it is the small free fraction (approximately 0.03% of total T4) that is generally recognized as the physiologically active fraction due to its ability to enter target cells (3,4). Once in the cells T4 influences calorigenesis and protein, lipid and carbohydrate metabolism. T4 also functions in the peripheral tissues as a pro-hormone by being further metabolized to the most active thyroid hormone, triiodothyronine (T3) and other inactive metabolites such as reverse T3 (5).

Local T4 levels may be altered by changes in the concentration of TBG, which is dependent on several non-thyroidal factors. Total T4 levels may be elevated when TBG concentration is increased, as in pregnancy, hepatitis, congenital TBG elevation, and administration of estrogens (oral contraceptives) (6). Conversely, total T4 levels may be reduced when the TBG concentration is decreased by such conditions as nephrosis, hepatic failure, congenital TBG deficiency, administration of androgens or large amounts of glucocorticoids (7). Despite the alterations in total T4 levels from the physiological states described above, thyroid function is not affected because the body acts to maintain constant levels of free T4 (3,4).

The ability to measure free T4 offers theoretical and practical advantages over the measurement of total T4 in the laboratory evaluation of thyroid status. These advantages are based on the two factors described previously. Firstly, the recognition that free T4 is the metabolically active form gives free T4 measurement a theoretical advantage to total T4 measurement in that it represents a more direct assessment of thyroid function. Secondly, whereas total T4 levels rise and fall with changes in TBG concentration, free T4 levels remain constant. Consequently, the measurement of free T4 more accurately reflects the true thyroid status.

The first laboratory techniques for measuring free T4 consisted of indirect methods such as the free thyroxine index (FTI) and the T4/TBG ratio. These tests involve the use of a total T4 determination in conjunction with a test which measures available TBG binding sites (T3 Uptake test) in the case of the FTI, and TBG concentration in the T4/TBG ratio. However, these indirect tests have limited diagnostic value in cases of abnormally high or low TBG levels and also involve the performance of two assay procedures (4,8).

A variety of methods have been developed to allow a direct measurement of free T4 which employ techniques such as equilibrium dialysis, ultrafiltration, and column chromatography, but these methods are generally too laborious and time-consuming for routine use in the clinical laboratory (8).

Immunoassay methods have gained wide acceptance as specific, sensitive and convenient alternatives to many tradional clinical chemistry methods, yet difficulties arose in applying immunoassay methods to the measurement of free T4 due primarily to the requirement that the original equilibrium between free and bound T4 must not be disturbed by the addition of assay reagent (4,8).

The Eclectica Free T4 assay employs a technology that allows the use of a conventional EIA methodology while minimizing the disturbance to the free and bound T4 equilibrium. Two key factors allow a direct measurement of free T4. They are: (1) a T4-alkaline phosphatase conjugate which binds to anti-T4 antibody but not significantly to TBG and other serum binding proteins; and (2) a monoclonal antibody with a high affinity for T4.

The Eclectica assays for the Eclectica analyzers consists of:

  1. Eclectica Free T4 Reagent Kit: specific reagents of Eclectica Free T4 kit to execute the test and to verify the standardization.
  2. Eclectica Free T4 Calibration Kit: for standardization.
  3. Eclectica Immunoassay Common Reagents Kit: for general chemistry reaction.
  4. Eclectica Immunoassay Wash Solution: Wash Solution specific for Immunological reaction.
  5. Eclectica Systemic Wash Solution: Wash Solution of Eclectica system.

In the Eclectica Free T4 assay, a mouse monoclonal anti-T4 antibody is used in an enzyme immunoassay system which incorporates magnetic solid phase separation.

All incubation times and reagent volumes are determined by an assay specific software protocol.

Fixed amounts of fluorescein-labelled anti-T4 antibody and T4 conjugated to alkaline phosphatase are added to the sample, control or calibrators.

The reactants are incubated at 37°C. During the incubation Free T4 in the sample, control or calibrators competes with the T4 conjugate for binding to the anti-T4 antibody.

At the end of the incubation period anti-fluorescein coupled to a magnetic solid phase is added in excess. This rapidly and specifically binds to the free T4-antibody complex and is sedimented in a magnetic field.

After aspirating the liquid phase and washing the solid phase, a solution of the enzyme substrate, phenolphthalein monophosphate is added to the incubation cell and the each cell incubated at 37°C. After incubation the enzyme reaction is stopped by the addition of a stop reagent and the intensity of the color developed is measured photometrically.The intensity of the color developed is inversely proportional, within the working range of the assay, to the concentration of Free T4 in the sample. The concentration of free T4 in a patient sample or control is then determined by interpolation from a stored standard curve.

Eclectica Free T4 Reagent Kit

Eclectica Free T4 Calibration Kit

Eclectica Immunoassay Common Reagents Kit

Eclectica Immunoassay Wash Solution

Eclectica Systemic Wash Solution

1700006 Eclectica Cleaning Kit

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