Total Thyroxine (T4) Test

The thyroid gland produces a hormone called thyroxine, which is also known as T4. This hormone plays a vital role in body functions like metabolism & growth. The test for T4 is of two types namely free T4 & total T4. In this case, we are considering total T4 which includes all the T4 hormones in the body including the T4 bonded to protein and the free T4 available in the body. When the thyroid gland overworks or underperforms then the T4 levels increase and decrease respectively. The overworking thyroid causes a disease called hyperthyroidism and underperforming thyroid gland causes a disease called hypothyroidism. Hence, the thyroxine-total test is done to detect hyperthyroidism, hypothyroidism & hypopituitarism.

A number of drugs can affect the levels of T4 in the blood like hormonal drugs containing hormones, such as androgen, estrogen, and birth control pills. Drugs used in treating thyroid conditions and drugs designed to affect thyroid, cancer drugs, steroids also affect the T4 levels in the blood. Hence, inform your doctor regarding all medicines that you are taking. Some medications might need to be temporarily stopped until the test gets over.

Elevated T4 levels beyond the reference range indicate hyperthyroidism or conditions like thyroiditis or toxic multi-nodular goitre. Decreased T4 levels below the reference range indicate hypothyroidism or fasting or malnutrition or iodine deficiency or illness or any medication causing the decrease in the hormonal levels.

About 1 ml or just 2 teaspoons of the blood sample will be drawn from your body. This test needs to be conducted in a well-equipped diagnostic lab or medical centre with Thyroxine- Total testing facility. The skin on the arm is cleaned with an alcohol pad. In the next step, the needle will be inserted into the body through the vein which is easily visible over the cleaned skin. The blood sample will be collected through the tube attached to the needle which contains the serum gel. The tube is separated from the needle and closed with a lid and with the patient’s name on it. The blood sample tube is shaken down to remove serum from the clot and then it is sent to the research laboratory for examination.