What Does Thyroid Test Result Indicate?

The thyroid gland is a pair of endocrine gland present in the throat area that regulates a large number of body functions. They secrete some of the most important hormones needed for normal functioning of the body. These hormones also help is controlling and regulation of other hormones in the body.

There are a number of laboratory tests that determine the function of thyroid glands. The most important tests for checking the function of thyroid gland are as follows:

Thyroid stimulating hormone test is a common test done by physicians for diagnosis and management of thyroid conditions. TSH is a measure of pituitary hormone that acts as a messenger to the thyroid gland. Pituitary glands regulate the production of thyroid hormone production by the thyroid glands by increasing or decreasing the production of TSH hormones, which in turn sends a message to the thyroid glands as needed.

TSH levels above the reference range indicate that the thyroid is underactive and it is not producing enough thyroid hormones, i.e. hypothyroidism or hypothyroid condition. TSH level below the reference range indicate that the thyroid glands are overactive and there is very production of thyroid hormones; i.e. hyperthyroidism or hyperthyroid condition. To summarise the above, elevated TSH level reveal underactive thyroid and reduced TSH level reveal overactive thyroid.

TSH level within the reference range, indicate that the thyroid glands are functioning normally and there is nothing to worry. However, if there are thyroid signs and symptoms, known family history of thyroid disease with evidence of abnormal T3 or T4 levels, or antibodies then the thyroid may not be considered as normal.

The reference range usually varies from laboratory to laboratory and also based on the geography of the area. The reference range is between 0.5 – 4.70 µIU/mL; however, some laboratories consider the reference range to be between 0.3 to 4.5.

Thyroxine or T4 is one of the most important hormones produced by the thyroid glands. It loses an atom by the process of monodeiodination to become T3 which is the usable form of T4. It is used up by the body cells to produce energy. Total thyroxine level indicates the total amount of T4 produced. Free thyroxine indicates the amount of thyroxine that is free, unbound and is available to be converted to T3.

T4 level above the reference range indicate that there is over production of thyroid hormone and the thyroid gland is over active; i.e. hyperthyroidism. T4 level below the reference range indicate that there is under production of thyroid hormone and the thyroid gland in under active; i.e. hypothyroidism. Levels with the acceptable “reference range” is considered normal.

Total T4 level is within 4.5 – 12.5 µIU/dL and free T4 level is between 0.8 to 1.8 ng/dL. However, these range varies from laboratory to laboratory and geographical condition.

Free T3 measures the free, unbound thyroid hormone available to be used by the cells for energy production. A large number of physician believes that free T3 reflects the patient’s hormonal status than total T3.

Free T3 levels above the reference range indicate over active thyroid or hyperthyroidism; whereas free T3 levels below the reference range indicate under active thyroid or hypothyroidism.

The following is the reference range for free T3 for adults

Free T3/ triiodothyronine: 2.3 – 4.2 pg/mL

Total T3 – 80 – 200 ng/dL

The reference range differs from laboratory to laboratory and also based on the geography of the area.

Reverse T3 test or R T3 test measures the total amount of reverse T3 present in the bloodstream.

Reverse T3 test is considered as a controversial test by many physicians. Elevated R T3 level, above the reference range indicate under active thyroid or dysfunctional thyroid glands. Under ideal circumstances, the level of reverse T3 should fall within the lower limits of the normal acceptable range. In certain cases, the ratio of T3 and reverse T3 are calculated for determining the condition.

The reference range for reverse T3 or R T3 typically is between 10 to 24 ng/dL.

The reference range differs from laboratory to laboratory and also based on the geography of the area.

Thyroid peroxidase antibodies (TPO) or anti thyroid peroxidase antibodies are antibodies that work against thyroid peroxidase which is an enzyme that helps in conversion of T4 to T3. It is also known as anti-thyroid microsomal antibodies or anti microsomal antibodies. These antibodies indicates presence of an underlying inflammation of the gland, tissue destruction or condition such as Hashimoto’s disease. These antibodies are also predominantly evident in other conditions such as post – partum thyroiditis.

Elevated levels of TPO, above the reference range indicate inflammation of the thyroid glands possibly due to Hashimoto’s thyroiditis. Under normal circumstances, these antibodies are detected in 95 percent of patients who are known to have Hashimoto’s thyroiditis and it about 50 to 85 percent of patients who are known to have Grave’s disease. It has been seen that the level of TPO in Hashimoto’s disease is higher than in Grave’s disease. In certain cases, it has been seen that that the individual may have elevated level of TPO; however, the levels of T4/T3 and TSH are within normal levels. This condition is known as euthyroid condition. In these cases, the patients are prescribed levothyroxine, for retarding the elevation of antibodies to prevent hypothyroidism.

The reference range of TPO is less than 35 IU/mL. The reference range differs from laboratory to laboratory and also based on the geography of the area.

TSI measures the total amount of antibodies present in the blood stream. TSI tends to cause a condition called as goitre, where the thyroid gland is simulated to enlarge and grow larger in size; as a result of which there is excessive secretion of thyroid hormone, leading to hyperthyroidism. This particular test is also termed as TSH receptor stimulating antibody test. It helps is detection of Grave’s disease and toxic multinodular goitre. This test also carried in pregnant patients with known history of Grave’s disease to eliminate the risk of the new born being born with Grave’s disease. It has been seen that in patients with Hashimoto’s disease, there is elevation of TSI (thyroid stimulating immunoglobulins) index.

Elevated levels of TSI reveal over active thyroid or hyperthyroidism due to Grave’s disease. In pregnant ladies, elevated levels of TSI indicate high risk of neonatal thyrotoxicosis or hyperthyroidism.

The reference range for TSI is less than or equal to 1.3 TSI index. The reference range differs from laboratory to laboratory and also based on the geography of the area.

Thyroglobulin is a type of protein that is produced the thyroid gland. The presence of thyroglobulin in the blood stream indicate that the patients still has some amount thyroid gland remaining back, either completely or partially after a surgery done in the past or post radioactive ablation.

This test is usually carried out in patients with thyroid cancer. It is done to determine production of thyroglobulin prior to the treatment and also to determine if the treatment is working fine and for determining the recurrence of the disease after treatment. Thyroid cancer both papillary and follicular produces thyroglobulin. Elevated levels of thyroglobulin indicate signs of recurrence of cancer. This test is also done, though less often, for determining presence of Grave’s disease and hyperthyroidism.

Low level of thyroglobulin is a normal finding and does not necessarily indicate presence of thyroid disease. Elevated level of thyroglobulin in patients with thyroid cancer indicates that the thyroglobulin level has to be monitored for detecting recurrence.

If the thyroglobulin levels are not at zero or close to zero after a thyroid surgery or after a radioactive iodine (RAI) treatment, it indicates that further treatment and management of the condition is required. If the level of thyroglobulin raises post treatment it is a sign of cancer reoccurrence. Drop is thyroglobulin level indicate that the treatment for Grave’s disease and hyperthyroidism treatment is working.

Elevated level of thyroglobulin may be seen in other thyroid disorders such as goitre, thyroiditis and hyperthyroidism; however, it is not a typical test done conventionally for diagnosis of these condition.

The expected range of thyroglobulin should be less than 0.1 ng/mL in complete absence of thyroid gland. The level is less than or equal to 33 ng/mL if the gland is still present. The reference range differs from laboratory to laboratory and also based on the geography of the area.

Thyroglobulin antibodies, also known as TgAb, as the name indicates they are antibodies found in the blood stream against thyroglobulin. These antibodies are found in about 10 percent of individuals with normal thyroid function and in about 15 to 20 percent of people with thyroid cancer. These antibodies are known to interfere with thyroglobulin (Tg) findings because of which it is important to monitor TgAb levels and Tg levels at regular intervals in thyroid cancer patients.

Elevated levels of TgAb indicate that the Tg test done is not accurate and cannot be taken into consideration for final conclusion. It may indicate that there is a possibility of the Tg level being actually higher than what the test result reveals.

The reference range for TgAb is below 4.0 IU/mL. The reference range differs from laboratory to laboratory and also based on the geography of the area.

Also Read:

• What is Chronic Lymphocytic Thyroiditis & How is it Treated?: Causes, Symptoms, Prognosis of Chronic Lymphocytic Thyroiditis
• Causes of Solitary or Single Thyroid Nodule
• Thyroid Gland Cancer: Causes, Symptoms, Treatment- Surgery, Harmone, Chemo Therapy
• Diagnosis of Small or Large Solitary or Single Thyroid Nodule
• Thyroid Disease: Types, Causes, Symptoms, Treatment, Prognosis, Epidemiology, Prevention
• What Causes Your Thyroid to be Underactive (Hypothyroidism)?