Normal T4 Levels

The thyroid gland is one of the most important endocrine glands in our body. The thyroid gland is stimulated into producing its hormones, T3 (Triiodothyronine) and T4 (Thyroxine or Tetraiodothyronine) by the pituitary gland.

Any kind of malfunctioning in the thyroid gland reflects in its levels of hormone production. Hence, this is one of the main reasons why tests are done to check T3 and T4 levels. These tests are important, as any sudden changes in the levels of thyroid hormone clearly points towards thyroid problems, which may have grave repercussions on the body.

What is T4?
As mentioned above, T4 is the hormone produced by the thyroid gland. It contains 4 iodine molecules, hence it's also called Tetraiodothyronine. The main function of T4 is to get converted into T3, which is more active hormone that is used by the cells in the body. There are two forms of T4 namely, Total T4 and Free T4.

Total T4 includes both the T4 that is bound by proteins as well as the free T4. On the other hand free T4 is the T4 that floats around the blood and is available for conversion into T3. The levels of Total T4 may be falsely raised due to changes in the protein levels.

This may happen because of several medications, including certain types of birth control pills, high dose of aspirin, etc. High levels of estrogen and pregnancy may also affect the Total T4 count. However, free T4 is not affected by any such medications.

• Normal Levels of T4 (Total) - 4.8 - 10.4
• Normal Levels of T4 (Free) - 0.8 - 1.7
• Lower T4 Levels - 0.5 - 5.5
• Higher T4 Levels - >11

*Please Note: The Laboratory reference ranges and normal ranges of T4 levels vary according to the measurements used in different labs. It is best to visit your doctor with the results for correct diagnosis.

Tests for Normal Levels of T4

Blood or Thyroid-stimulating Hormone (TSH) Test
In this test, the person's blood sample is taken from a vein, normally from the cubital fossa, the anterior side of the elbow. Then, this blood is sent to the lab to check free T4 (when T4 is not attached to a transportation protein) levels.

Radioimmunoassay (RIA)
This test is commonly referred to as T7. It is preferred to a blood test to check T4 levels, as it corrects any kind of alterations which may affect the outcome of the test, like the presence of certain medications in the blood like aspirin, birth control pills etc. This test directly shows the amount of thyroxine i.e., T4 in the blood.

Although it is relatively accurate even in cases where the person is on thyroid medication, it is advisable to avoid any thyroid medication prior to the test to ensure that the results received, accurately correspond to normal T4 levels, especially in women.

Interpreting Abnormal T4 Levels

Any kind of shift from normal levels are indicative of two things - either deranged functioning of the thyroid gland or unbalanced functioning of the pituitary gland. In very rare cases, there may be deranged functioning of both the glands.

However, abnormal functioning of the pituitary gland can be ruled out by doing TSH blood test. Thus, if a test for thyroxine shows abnormal levels of this hormone, then the report needs to be further interpreted.

Low Levels: T4 levels that are below normal are indicative of hypothyroidism. In this condition, the T4 level is below and the TSH level is above the normal range. This condition may result from inadequate stimulation of the thyroid gland or due to underactivity of the thyroid gland.

Even in certain other conditions, like intake of certain drugs, Hashimoto's disease, severe illness and malnutrition etc., shift from normal T4 ranges may occur.

High Levels: High thyroxine levels are basically indicative of overactivity of the thyroid gland, or hyperthyroidism. In this situation the T4 levels are raised above normal while the TSH levels are below the normal range.

Hyperthyroidism could occur due to various problems like, pituitary adenoma, thyrotoxicosis, Graves' disease, iodine induced hyperthyroidism etc.

When both the Total T4 and TSH levels are low, your doctor might look for pituitary problems. If the test is done for the check of Free T4 level and it is less than normal, it may indicate hypothyroidism.

Disclaimer: This story is for informative purposes only and does not, in any way, intend to replace the advice of a medical expert.