Thyroid Stimulating Hormone TSH With Reflex to Free T4

Also known as

Thyroid Screening, T4., TSH with reflex to FT4, TSH reflex

This test is used by the doctor to help how the thyroid gland is functioning. It aids in the diagnosis of thyroid disease and assesses how the thyroid treatment plan is progressing. In some cases, this test is used by the doctor to diagnose congenital hypothyroidism in newly born babies.
This test is ordered by the doctor when he or she feels that the patient has symptoms of thyroid disease. It may also be ordered when the patient has an enlarged thyroid – also known as goitre – or if the patient has a thyroid nodule – this is a small lump on the thyroid gland, which may a fluid-filled cyst or solid. In addition, the test is ordered as a follow up on an abnormal TSH test or when a patient is being treated for a thyroid disorder.
This is a blood test. The technician draws a blood sample from a vein in the arm using a syringe. In the case of newly born babies, the heel of an infant is pricked.
There is no special preparation needed for the test. However, it must be noted that some medications, supplements and multivitamins can adulterate the result of the test. Therefore, it is imperative to inform the doctor of any prescription or over the counter medication the patient is taking. Furthermore, if the patient is undergoing treatment for thyroid disease – such as taking thyroid hormone treatment – it is advised that the blood sample be drawn before taking the dosage of the treatment. In addition, if a patient is acutely ill, thyroid testing results may be affected. Thyroid testing should, therefore, be avoided in patients who have been hospitalised or simply deferred until after the patient has recovered from his or her affliction.
This test measures T4. T4 or thyroxine is one of the two primary hormones made by the thyroid gland. The other hormone is T3, also known as triiodothyronine. The thyroid gland is a small, butterfly-shaped organ that is found at the base of the throat. The gland lays flat across the windpipe. The two hormones work together to regulate the rate at which the body utilises energy. T4 is mostly found in the blood bound to protein. A small amount is unbound or free. This is the biologically active form of the hormone. The thyroid gland mostly makes T4. This hormone is relatively inactive and is converted in T3 – its active variant – in the liver and other tissues. The body regulates T4 levels using a feedback system. The feedback system helps in maintaining stable amounts of thyroid hormones in the blood. T3 and the thyroid-stimulating hormone work with the regulatory hormone thyrotropin-releasing hormone as part of the feedback system. The system works in the following way: when the levels of thyroid decrease in the blood, the pituitary gland makes TSH in response to TRH stimulation. TSH, in turn, stimulates the thyroid by binding to the TSH receptor to produce and release T4 and T3. On the other hand, when thyroid hormone levels rise in the blood, the pituitary glands make less TSH, and the thyroid gland makes less T4 and T3. When the hypothalamus, thyroid, pituitary are working normally, then thyroid production is regulated in order to maintain stable levels of thyroid hormones in the blood. However, if the thyroid gland does not make an adequate amount of T4 and T3 due to thyroid dysfunction or insufficient TSH, then the patient exhibits symptoms of hypothyroidism. When the thyroid gland produces excessive T3 and T4, the patient experiences symptoms related to hyperthyroidismGraves disease is the most common cause of hyperthyroidism. Hyperthyroidism and hypothyroidism occur due to thyroid cancer, thyroiditis or the increase or decrease production of TSH. This test can be used by the doctor to monitor the effect of these conditions on thyroid hormone production.
The test is by the doctor to:
  • Aid in the detection of too much or too little thyroid hormone (hyperthyroidism and hypothyroidism) and diagnose the cause
  • Help identify between different thyroid disorders
  • Help in evaluating the effectiveness of treatment in a person with a known thyroid disorder
  • Monitor individuals with thyroid cancer, in which the tumours respond to TSH. TSH and T4 levels will be regularly checked to make sure that enough thyroid hormone is being given to keep TSH low without making T4 too high.
  • Aid in the evaluation of the function of the pituitary gland (occasionally)
The test is ordered when the patient has symptoms of hyperthyroidism or hypothyroidism, goitre, thyroid nodule and abnormal TSH. Symptoms of hyperthyroidism include:
  • Increased heart rate
  • Anxiety
  • Weight loss
  • Difficulty sleeping
  • Tremors in the hands
  • Weakness
  • Diarrhoea (sometimes)
  • Light sensitivity, visual disturbances
  • There may be puffiness around the eyes with dryness, irritation, and, in some cases, bulging of the eyes.
  • Menstrual irregularity in women
Symptoms of hypothyroidism include:
  • Weight gain
  • Dry skin
  • Constipation
  • Cold intolerance
  • Puffy skin
  • Hair loss
  • Fatigue
  • Menstrual irregularity in women
This test may also be ordered alongside other thyroid tests if the patient is undergoing treatment for thyroid disease. If a pregnant woman has a thyroid disorder, the doctor may order testing early and late in the pregnancy and also after the delivery.
The results of the test are evaluated in conjunction with other thyroid testing results. In general, a high TSH with reflex indicates an overactive thyroid gland, and a low-test result indicates an underactive thyroid gland. The test results are not diagnostic, and the doctor needs to perform some additional tests to identify why a deficiency or excess may occur. Both increased and decreased test results are linked to a range of temporary and chronic thyroid conditions. Lower results for T4 alongside a low TSH test result or a high T4 and high TSH result indicate a disease related to the pituitary gland.
Related Tests

T3 (Free and Total), Thyroid Panel, Thyroid Antibodies, Thyroid-stimulating Hormone (TSH), Calcitonin

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