Introduction

Thyroid hormones mainly include thyroxine, also known as tetraiodothyronine (thyroxine, 3, 5, 3', 5'-tetraiodotyyronine, T4), and triiodothyronine (3, 5, 3'-triiodothyronine, T3). Both are tyrosine iodine compounds. Additionally, the thyroid gland produces a very small amount of reverse T3 (3, 3, 5'-T3 or reverse T3, rT3). The molecular structure of T4 is illustrated in the figure.

Healthy Thyroid Function: A Review of Anatomy and Physiology - Absolute Health & Wellness (absolutehealthparis.com)

After entering the bloodstream, thyroid hormones that do not bind with thyroxine-binding globulin (TBG) in plasma are known as free thyroid hormones (Free Thyroxine, FT4). FT4 is the biologically active form of thyroid hormone and directly reflects the functional status of the thyroid gland. It is generally unaffected by external iodine, TBG concentration, or binding capacity changes. Clinical evidence suggests that serum T4 concentration measurements are susceptible to TBG concentration changes. When TBG concentration increases, T4 content increases, but the concentration of physiologically active FT4 does not increase. In such cases, there is no hyperthyroidism. When TBG concentration decreases, T4 concentration decreases, but FT4 concentration does not decrease, and thyroid function remains unchanged.

T4 Chemical Structure
Thyroxine, T4 or Levothyroxine Thyroid Hormone Molecule. Prohormone of Thyronine T3. Skeletal Formula. Stock Vector - Illustration of composition, hydrogen: 239581151 (dreamstime.com)

Clinical Diagnostic Significance

Free thyroid hormone immunoassays are of significant clinical importance. FT4 is the biologically active form of thyroid hormone, and its serum concentration more directly reflects the thyroid's functional status. Therefore, FT4 measurement is one of the ideal thyroid function tests. Specifically, it is significant for:

1.Diagnosing hypothyroidism.

2.During treatment for hyperthyroidism or hypothyroidism, monitoring FT4 levels aids in guiding medication dosage, prognosis, recurrence, etc. FT4 measurement is also significant for follow-up treatment of neonatal hypothyroidism.

3.Non-thyroidal illness syndrome, typically characterized by decreased T3 and T4 levels and increased rT3 levels, with normal sTSH levels but no clinical signs of hypothyroidism, is also known as euthyroid sick syndrome. The liver, a primary site for thyroid hormone metabolism, often exhibits significant thyroid hormone metabolic disorders in patients with liver diseases. For example, in cirrhotic patients, T4 to T3 conversion disorders can lead to decreased serum T3 levels, while serum FT4 can be normal. Observing serum FT4 and FT3 concentrations can provide insights into the progression and changes in cirrhotic patients' conditions and guide treatment. Changes in serum FT4 and FT3 concentrations can be indicators for clinical evaluation of severe hepatitis.

Bioeast Product Introduction

1. Bioeast Product Recommendation

For thyroid hormone testing, Bioeast Biotech offers a T4 monoclonal antibody and corresponding T4 synthetic antigen, as shown in Table 1.

Table 1: Pairing Recommendations for Free Thyroid Hormone Competitive Immunoassay System Development

2. T4 Antibody Performance Analysis

Competitive methods are generally used for developing free thyroid hormone test kits. Options include coating antibodies on magnetic beads and labeling antigens, or coating antigens and labeling antibodies. Bioeast's internal laboratory has validated the application of Bioeast's T4 raw materials on a chemiluminescence platform, with the following results:

(1)Reaction Mode Ⅰ- Antibody Magnetic Bead Coating

Bioeast's internal laboratory used the T4101 monoclonal antibody as a capture antibody for reagent performance analysis. The results showed good performance on the chemiluminescence platform, with precision <3.5%. A comparison with 107 clinical samples showed good correlation with the Reference kit (R²=0.9562).

• Precision Test:

Testing two clinical samples 10 times with a self-developed test kit showed good precision (CV<3.5%). See Figure 1 for results.

• Correlation with Reference Kit:

Testing 107 clinical samples with the self-developed kit and Reference kit, linear regression analysis showed significant correlation between the two kits (R²=0.9562). See Figure 2 for results.

(2) Reaction Mode II - Antigen Magnetic Bead Coating

• Precision Test:

Testing two clinical samples 10 times with a self-developed test kit showed good precision (CV<3.5%). See Figure 3 for results.

• Correlation with Reference Kit:

Testing 107 clinical samples with the self-developed kit and Reference kit, linear regression analysis showed significant correlation between the two kits (R²=0.9604). See Figure 4 for results.

Conclusions