TFTs are used to help diagnose hypo- and hyperthyroidism which can be due to various thyroid diseases, or occasionally, disorders of the pituitary gland or to monitor the response to treatment of these conditions.
In some laboratories, the initial blood test for thyroid disorders is a TSH test. If your TSH concentration is abnormal, it will usually be followed up with a FT4 measurement (or occasionally total T4). In some cases FT3 (or total T3) will also be performed. Often, the laboratory will do this follow-up testing automatically, and this is known as reflex testing. This saves your doctor time from having to wait for the results of the initial test and then requesting the additional testing to confirm or clarify a diagnosis. Follow-up tests are often performed on the original sample that was submitted when the initial test was requested.
TFTs may be requested as part of a health check-up or when symptoms suggest hypo- or hyperthyroidism due to a condition affecting the thyroid. They may also be requested following commencement of treatment for any detected thyroid condition.
Signs and symptoms of hypothyroidism may include weight gain, dry skin, constipation, cold intolerance, puffy skin, hair loss, fatigue, and menstrual irregularity in women.
Signs and symptoms of hyperthyroidism may include increased heart rate, anxiety, weight loss, difficulty sleeping, tremors in the hands, weakness, and sometimes diarrhoea. There may be puffiness around the eyes, dryness, irritation, and, in some cases, bulging of the eyes.
If the thyroid gland fails and the concentrations of thyroid hormones fall, a feedback system will result in increased TSH release from the pituitary gland. Similarly, if the thyroid gland becomes overactive and increased amounts of thyroid hormones are released, TSH production will be suppressed. If the feedback mechanism is not functioning properly, as can occur with a variety of illnesses not directly affecting the thyroid, the release of TSH may be reduced and the concentation of thyroid hormones in the blood may fall as a result. Very rarely, TSH concentrations may be increased, due to a tumour of the pituitary, in which case the thyroid will make and release inappropriate amounts of T4 and T3, and the patient may experience symptoms associated with hyperthyroidism. If there is decreased production of thyroid hormones, the patient may experience symptoms of hypothyroidism.
The following table summarises test results and their potential meaning.
The thyroid tests offered may vary between hospital laboratories. For some, a strategy is employed to perform one initial test followed up others only if needed, and in other laboratories, initial measurement of both FT4 and TSH, with the addition of FT3 in selected cases.
This article was last reviewed on 26 April 2012. | This article was last modified on 3 October 2014.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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