Thyroid (total) array

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Intended Use

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 hormone 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 TTHY array successfully quantitatively tests for TSH, TT4 and TT3 simultaneously.

REFERENCES

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

 

Thyroid Stimulating Hormone (TSH) Assay

Intended Use

The Evidence Thyroid Stimulating Hormone (TSH) assay has been designed for the in vitro 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

 

Total Triiodothyronine (TT3) Assay

Intended Use

The Evidence Total Triiodothyronine (TT3) (free and bound) assay has been designed for the in vitro quantitative measurement of TT3 in serum. Measurements of thyroid hormone produced by the anterior pituitary are used in the diagnosis of thyroid and pituitary disorders.

Clinical Significance

Triiodothyronine (T3) was originally identified in human plasma by Gross and Pitt-Rivers in 1952 (3). It is derived primarily from Thyroxine (T4) through deiodination in peripheral tissues. T3 is considered to be the active hormone, and T4 a prohormone.

Although T3 is only 1-2% of the concentration of T4 in serum, there is less bound to proteins in the serum. The concentration of Free Triiodothyronine (FT3) is about one-quarter of the concentration of Free Thyroxine (FT4) but since T3 has about four times the biological activity of T4, they represent similar levels of thyroid hormone activity in the blood.

Both T3 and T4 increase the rate of metabolic activity in many tissues of the body. T3 is essential for normal physical and mental development throughout childhood and for controlling the rate of metabolic activity in adults (1).

The minute amounts of T3 and T4 which are not bound to proteins, circulate in a free state and they are regarded as metabolically active fractions as they can pass into the cells of target tissues.

Despite the small quantities of T3 present in human serum, it plays an important role in the maintenance of the euthyroid state (4). T3 is used to investigate thyroid function. It is an important follow up test for patients that appear to be hyperthyroid. It is also useful for detecting hyperthyroidism where clinical symptoms indicate the condition but FT4 is normal. For example, in T3-toxicosis, T3 is elevated but T4 is not (1).

Principle

The Evidence TT3 assay is a competitive chemiluminescent immunoassay for the detection of TT3 in human serum.

REFERENCES

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

2. Hopton MR, Ashwell K, Scott IV and Harrop JS, Serum Free Thyroxine concentrations and free thyroid hormone indices in normal pregnancy, Clinical Endocrinology; 1983; 18:431-437

3. Gross J, and Pitt-Rivers R, The Identification of 3:5:3' -L-triiodothyronine in human plasma, Lancet, 952; 1:439

4. Larsen PR, Triiodothyronine: Review of Recent Studies of its Physiology and Pathophysiology in Man, Metabolism, 11 November 1972; 21(11): 1073-1092

Total Thyroxine (TT4) Assay

Intended Use

The Evidence Total Thyroxine (TT4) assay has been designed for the in vitro quantitative measurement of total (free and bound) thyroxine in serum. Measurements of thyroid hormone produced by the anterior pituitary are used in the diagnosis of thyroid and pituitary disorders.

Clinical Significance

Thyroxine (T4), full name tetraiodothyronine, is the principle hormone produced in the thyroid gland. Iodine is an essential requirement for thyroid hormone production and it is the coupling of two diiodinated tyrosine molecules that produces T4.

T4 is also considered a prohormone for the more metabolically active thyroid hormone triiodothyronine (T3) but it is probably active itself when bound to receptors. Both T3 and T4 occur naturally as the L-isomer, they are found in the serum and thyroid and they increase the rate of metabolic activity in many tissues of the body. Although T4 is present at a higher concentration than any other thyroid hormone in the body, it is several times less biologically active than T3 (1,2).

T4 and T3 make up the major fraction of circulating thyroid hormones. They are transported in the plasma attached by non-covalent bonds to plasma proteins, namely, thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA) and albumin and they exert their stimulatory effects on cell metabolism through actions on gene transcription. Only a minute fraction of T4 (0.03%) and T3 (0.5%) are unbound. The total concentration of thyroid hormone in the blood is therefore dependant on the concentration of specific binding proteins as well as the functioning of the thyroid gland.

The concentration of T4 in serum or plasma is an important indicator of thyroid status. In most cases, T4 is reduced in hypothyroidism and increased in hyperthyroidism (1).

Principle

The Evidence TT4 assay is a competitive chemiluminescent immunoassay for the detection of TT4 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