A brief explanation of how the thyroid is responsible for metabolism will make it clears to which blood markers to test. The brain, specifically the anterior pituitary gland, secretes a hormone called Thyroid Stimulating Hormone or TSH. This in turn travels to the thyroid gland which is found in the lower third of the neck and activates the production of a type of thyroid hormone called T4. T4 is then released and travels by blood to the cells in the body where it is actively converted into another thyroid hormone, T3. The conversion requires a number of conditions and co-factors to be present such as selenium and zinc. T3 is the most active thyroid hormone and is responsible for metabolism – energy production – in the body. How this translates, for example, is maintaining optimum weight, having energy through out the day, keeping the body at a constant temperature and maintaining a stable mood.
When T4 levels are low, the brain detects this and sends the signal for more TSH to be produced. This results in an increased production in T4 and thus a rise in T3 levels. In a case where hypothyroidism is missed, often only TSH is tested alone, and the value falls within the broad “normal” range. Many people will display a high-normal TSH but have low blood levels of T4 and T3 which are not routinely tested, therefore not treated.
In some instances, T3 is converted into an unusable form of thyroid hormone called reverse T3 (rT3). This occurs often when there is a high level of physical or emotional stress and the stress hormone cortisol is high. rT3 cannot be used for promoting metabolism therefore when it is high, symptoms of hypothyroidism are usually present. Levels of rT3 are not regularly tested in conventional medicine.
The last important component to comprehensive thyroid testing is looking at the production of antibodies against the thyroid. It is estimated that about half of all hypothyroid cases are caused by an auto-immune attack on the thyroid gland. In cases where this causes mostly hypothyroid symptoms, it is called Hashimoto’s thyroiditis and is diagnosed by the presence of anti-thyroid peroxidase antibodies (anti-TPO). Many people with Hashimoto’s will have high levels of a second type of antibody that targets the protein thyroglobulin (anti-TG). When providing a complete evaluation of thyroid function and health, testing for thyroid antibodies is recommended. Grave’s disease is another example of an auto-immune thyroid condition, however it results in hyperthyroidism.
In order to get the most comprehensive evaluation of thyroid function, a minimum of four blood markers should be tested. TSH, T4, T3 and anti-TPO make up a standard thyroid panel. Sometimes the addition of rT3 and anti-TG are included and can add valuable information. Blood should be drawn in the morning but does not require fasting overnight. Thyroid levels fluctuate throughout the day but are most stable before noon in the average person. If medication is currently being taken for hypothyroidism, consultation with the doctor is advised to determine if medication should be taken before or after the blood draw.
Those individuals on thyroid medication can also benefit from testing more thoroughly. Many cases of Hashimoto’s thyroiditis are missed upon initial diagnosis because antibodies were not checked. Other common findings when testing hypothyroid patients are that T3 levels are not optimal and the addition of other thyroid medications or herbs will greatly benefit thyroid health and metabolism.
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Yours in Health,
Dr. Jennifer Luis BSc, BEd, ND