Thyroid (free) array

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Intended Use

The Evidence thyroid arrays are to be used for the in vitro simultaneous quantitative detection of multiple related thyroid immunoassays in parallel from a single patient sample.

Clinical Significance

The thyroid gland lies just below the thyroid cartilage in the anterior neck. Normal thyroid hormones status is critical for the health of both children and adults. Thyroid hormones play very important regulatory roles in almost every tissue in the human body. In infancy and childhood thyroid hormone is essential for normal physical and mental development as well as growth. In the adult, thyroid hormones control protein synthesis, oxygen consumption, heat generation and overall metabolic activity. Therefore an imbalance in these hormones can have a detrimental effect and can be identified in a great number of disease states (1).

Principle

The Evidence analyser is a fully automated Biochip Array System. It performs simultaneous quantitative detection of multiple analytes from a single patient sample and therefore carries out sample assays much faster and efficiently than conventional laboratory analysers. The core technology is the Randox Biochip, a 9 mm (2) solid substrate containing an array of discrete test regions. A combination of competitive and sandwich chemiluminescent immunoassays is employed for the thyroid array. The light signal generated from each of the test regions on the biochip is detected using state-of-the-art digital imaging technology.

Several different immunoassay based multi-analyte panels have been developed for use on Evidence. The Evidence Thyroid Free Array successfully quantitatively tests for TSH, FT4 and FT3 simultaneously.

REFERENCES

1. Wild, D. The Immunology Handbook, Nature Publishing Group, United Kingdom, pp 497-520

 

Free triiodothyronine (FT3) Assay

Intended Use

The Evidence Free triiodothyronine (FT3) test is intended for the in vitro quantitative measurement of free triiodothyronine (not protein bound) in serum. Measurements obtained using this device are used in the diagnosis and treatment of disease such as hyperthyroidism.

Clinical Significance

A minute amount of thyroid hormone remains unbound to serum proteins, instead circulating in the blood in a free form in reversible equilibrium with the bound form. It is the free form that is able to cross the cellular membrane exerting its effect on the body tissues (1).

The concentration of Free Triiodothyronine (FT3) in the blood depends on the concentrations of Total Triiodothyronine (TT3) and the thyroid hormone binding proteins. Clinical studies have shown that FT3 is a better indicator of hyperthyroidism than TT3 as it is independent of thyroid hormone binding protein concentrations (2). Although changes in the binding proteins affect both the total hormone concentration and the free hormone circulating, in the euthyroid person the absolute concentration of free hormone remains constant (1). FT3 has been referred to as a more relevant indicator of thyroid function than TT3.

It wasn't until recently that it became easier to measure FT3 directly. Like TT3, FT3 is an important test for diagnosing or monitoring hyperthyroidism. The free hormone concentration is in general high in thyrotoxicosis, low in hypothyroidism and normal in euthyroidism, even in the presence of dramatic changes in the serum protein thyroxine-binding globulin (TBG) concentration.

Principle

The Evidence FT3 assay is a competitive chemiluminescent immunoassay for the detection of FT3 in human serum.

REFERENCES

1. Degroot LJ, Larsen PR and Hennemann G, The Thyroid and Its Diseases, sixth edition, Churchill Livingstone, New York, Edinburgh, London, Madrid, Melbourne, San Francisco, Tokyo, 1996;

2. Wild, D. The Immunology Handbook, Nature Publishing Group, United Kingdom, pp 497-520

 

Free Thyroxine (FT4) Assay

Intended Use

The Evidence Free Thyroxine (FT4) test is a device intended for the in vitro quantitative measurement of free (not protein bound) thyroxine (thyroid hormone) in serum. Measurements of thyroid hormone produced by the anterior pituitary are used in the diagnosis of thyroid and pituitary disorders.

Clinical Significance

Free T4 (FT4) is the biologically active, unbound fraction of Total T4 (TT4) and it is present in the blood in minute concentrations. Bound T4 circulates at 5,000 times the concentration of FT4. Some clinicians prefer to measure FT4 instead of TT4 since the concentration of FT4 is independent of the concentration of binding proteins. FT4 assays can be used to test thyroid function on its own whereas it is recommended that TT3 and TT4 are both measured.

Like TT4, FT4 is used in the investigation of patients suspected of thyroid disorders. It can also be used in the monitoring of patients undergoing treatment (1).

Since the FT4 is generally accepted to be the metabolically available T4, a measurement of the serum FT4 concentration seems to be preferable for evaluation of thyroid function, especially when TT4 is affected by changes in the concentration of the circulating binding protein Thyroxine-binding globulin TBG (2,3). In most cases, FT4 is increased in hyperthyroidism and decreased in hypothyroidism.

Principle

The Evidence FT4 assay is a competitive chemiluminescent immunoassay for the detection of FT4 in human serum.

REFERENCES

1. Wild, D. The Immunology Handbook, Nature Publishing Group, United Kingdom, pp 497-520.

2. Bakker AJ and Terpstra I, Total over free Thyroxine ratio: prediction of Thyroxine binding globulin, Ann Clin Biochem, 1982; 19: 94-100.

3. Ramsden DB, Sheppard M C and Hoffenberg R (1982), Free thyroid hormones in genetic disorders of their binding proteins and comments on free thyroxine assay, Elsevier Biomedical Press; 1982: 187-193.

 

Thyroid Stimulating Hormone (TSH) Assay

Intended Use

The Evidence Thyroid Stimulating Hormone (TSH) assay has been designed for the quantitative measurement of TSH in serum. Measurements of thyroid hormone produced by the anterior pituitary are used in the diagnosis of thyroid and pituitary disorders.

Clinical Significance

All aspects of thyroid gland function are controlled by thyrotropin, also known as thyroid stimulating hormone (TSH). TSH is a 29 kDa glycoprotein hormone consisting of two subunits, an a and a b chain and it is secreted by the anterior pituitary gland in response to the hypothalamic tripeptide, TRH (1,2). The action of TSH requires it to bind to a TSH-specific membrane receptor, which will activate adenylate cyclase through a G-protein coupled system (2). TSH regulates thyroidal secretion of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3), which in turn exert a negative feedback on the pituitary and hypothalamus. TSH is controlled by the negative feedback system thereby maintaining a constant concentration of free thyroid hormone in serum.

In patients with diminished thyroid function, the feedback system operates at a lower level which can result in a rise in TSH concentration in the blood. This is unless the disorder is primarily of hypothalamic or pituitary origin.

Measurement of serum TSH is a valuable test in the diagnosis of thyroid secretion. An imbalance in TSH can be caused by a variety of disease states. For example, in hyperthyroidism, T4 and T3 are increased causing TSH secretion to be suppressed. TSH has been suggested to be the most sensitive indicator of hypo- or hyperthyroidism (1,3).

Principle

The Evidence TSH assay is a sandwich chemiluminescent immunoassay for the detection of TSH in human serum.

REFERENCES

1. Wild, D. The Immunology Handbook, Nature Publishing Group, United Kingdom, pp 497-520.

2. Degroot LJ, Larsen PR and Hennemann G, The Thyroid and Its Diseases, sixth edition, Churchill Livingstone, New York, Edinburgh, London, Madrid, Melbourne,San Francisco, Tokyo, 1996.

3. Burger HG and Patel YC, The Value of Serum Thyrotrophin measurement in the diagnosis and management of hypothyroidism, Medical Journal of Australia, August 5 1972; 2: 293-297.