Thyroid Testing

by Sam Malone


Thyroid tests evaluate, as to whether the hormone production is underactive, normal or overactive. Hormones for various metabolic processes are synthesized by the thyroid gland. The condition of the thyroid gland is determined by various thyroid level testing. Thyroid hormones are synthesized by the thyroid gland.

Around 80% of the hormone produced is thyroxine (T4) hormone. Radioimmunoassay determines T4 content, in turn assesses the thyroxine levels in the blood. This is a reliable indicator of the functioning of the thyroid, provided, the individual abstains from thyroid medications. T3 or triiodothyronine is also assessed by radioimmunoassay. Greater T3 levels and normal T4 levels might also indicate normal functioning.

Thyroid binding globulin (TBG), is a protein to which the thyroid hormones bind to in the blood. Change in these protein levels changes the T3 or T4 levels, and not the hormone activity. Pseudo elevation of T4 levels is sometimes seen and this is attributed to the reduced or increased TBG levels. Such individuals are falsely diagnosed as hypothyroid or hyperthyroid patients.

Immunoradiometric assay is a typical thyroid testing technique in humans, used to evaluate the pituitary synthesis by Thyroid stimulating hormone (TSH). Low levels of TSH have the capacity to maintain a normal functioning of the thyroid gland. Malfunctioning of the thyroid gland resulting in hypothyroidism, might result in abnormal TSH and normal T3 and T4 levels. Generally, the thyroid tests (T3 RIA and T4 RIA) and TSH are utilized to assess the thyroid gland functioning.

TRH (TSH Releasing Hormone) is synthesized by the hypothalamus. TSH synthesis is increased by administration of TRH. On administration of TRH, individuals with excessive thyroxine and triiodothyronine secretion do not show a peak in the thyroid stimulating hormone. The quantity of iodine absorbed by the thyroid, is measured by iodine uptake scan. This is considered in concurrence with blood tests.

Administration of a radioisotope to individuals and evaluating the performance action of the gland is done by a thyroid scan. This aids in measuring the goiter size, its presence at the neck base and the follow-up of these patients. A biopsy is done to checkout if a nodule is benign or malignant. High frequency waves are utilized in identifying nodules and this is referred to as thyroid ultrasound.

Thyroid antibodies are increased in a condition called Hashimoto’s thyroiditis. The disorder results in antibodies or vice versa is unknown. A radioimmunoassay determines the presence of cancer. Fine needle aspiration (FNA) biopsy is done to diagnose cancer. Certain nodules are termed ‘suspicious’ and undergo biopsy for further diagnosis.


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