T4-Total Thyroxine Serum Test

Total T4 test is done along with TSH to
1. Diagnose thyroid disorders both overt & subclinical
2. Monitoring patients on thyroid replacement therapy
In a very small group of patients only T3 & FT3 is increased.
In pregnancy due to increase in thyroglobulin and decrease in albumin may cause increase of T3 & T4 levels, without actually impacting body functions hence testing FT3 and FT4 is more representative

Your doctor may order a T4-Total Thyroxine Serum test to:

• Check the level of thyroxine (T4) in the blood. This is done to help diagnose and monitor thyroid disorders, such as hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid).
• Monitor the effectiveness of treatment in people being treated for thyroid disorders. It can also be used to check for any potential side effects of the medications.

Total T4 test measures levels of FT4 hormone in blood

Total T4 test requires a blood sample. A tourniquet (elastic) band is placed tightly on the upper arm. The patient is then asked to make a fist. This helps in the build-up of blood filling the veins. The skin is disinfected before needle insertion and the blood sample is collected in vacutainer.

High TSH & high T3/FT3 and T4/FT4: Thyroxine replacement therapy; pituitary adenoma; drugs like heparin, amiodarone, beta blockers, steroids; neonates; resistance to thyroid hormones
High TSH & low T3/FT3 and  T4/FT4: Autoimmune thyroiditis, thyroidectomy, post-radiation, iodine deficiency, thyroid infiltrating tumour/ amyloid
Low TSH & Low T3/FT3 and T4/FT4: Central hypothyroidism, non-thyroidal illness
Low TSH & High T3/FT3 and FT4: Grave's disease, toxic multinodular goitre, toxic adenoma, thyroiditis, drugs, hyperemesis gravidarum & hydatiform mole, congenital hyperthyroidism

To perform the T4-Total Thyroxine Serum test, blood is drawn from a suitable vein on the inside of the elbow. The injection site is cleaned with cotton dipped in alcohol. A tourniquet is tightly fastened around the upper arm to put pressure on the vein and restrict blood flow. As a result of this, the veins below the band get filled up with blood.  A needle is then inserted into the vein and the drawn blood is collected in an air-tight vial. The band is then removed to restore circulation. A slight prick may be felt upon insertion of the needle. Bruising or tenderness at the injection site, if any, usually resolves with some time.

No special preparations are required for the T4-Total Thyroxine Serum test. However, your healthcare professional may ask you to stop taking any medication that may affect your results.

The normal values of this test may vary slightly between different laboratories. However, the typical range lies between 4.5 and 11.2 mcg/dL.

• Higher than normal T4 results and low TSH levels indicate hyperthyroid conditions like Graves’ disease, chronic or subacute thyroiditis, toxic multinodular goitre, germ cell tumours, iodine-induced hyperthyroidism, or trophoblastic disease.
• On the other hand, lower than-usual levels indicate hypothyroidism, malnutrition, illness all over the body, or the use of medications such as dexamethasone, propranolol, iodine, lithium, methimazole, etc.

The T4-Total Thyroxine Serum test can be performed at any time, but is usually done in the morning as the levels of thyroxine will be the highest during that time

Thyroid disorders refer to conditions that affect our thyroid gland. The thyroid is a small gland located in the neck that is responsible for producing hormones to regulate the body's metabolism. Common thyroid disorders include hypothyroidism and hyperthyroidism.

Thyroid disorders can range from diseases such as goitre to life-threatening conditions such as thyroid cancer. The two most common thyroid-related conditions involve abnormal thyroid hormone production leading to hypothyroidism (lower than normal hormone production) and hyperthyroidism (higher than normal hormone production). Both conditions require medical care and are serious.

All thyroid disorders can be treated. However, treatment involves being on medication consistently to maintain normal thyroid function. Most patients with thyroid cancer can get a complete cure through radioactive iodine treatments and surgery.

For people with thyroid disorders, it would be best to avoid certain foods such as soy, iodine-rich foods, high-fibre foods, and calcium and iron supplements.

Your healthcare provider may order a T4-Total Thyroxine Serum test if you are showing any signs of a thyroid disorder.

You must get the T4-Total Thyroxine Serum test done if you are showing any signs of an underactive thyroid such as:

• Gaining weight
• Excessively dry skin
• Feeling cold
• Feeling tired
• Feeling depressed
• Are constipated
• Having weak muscles
• Thinning hair‌
• Irregular periods‌

Besides an underactive thyroid gland, an overactive gland also causes many uncomfortable symptoms such as:

• Uninitiated Weight Loss
• Fast heart rate
• Feeling nervous or anxious
• Feeling hungrier than usual
• Feeling hot
• Having diarrhoea
• Difficulty sleeping
• Shaking hands
• Thinning hair
• Dry and puffy eyes 

Total Thyroxine (TT4) test

o   Thyroxine (T4) test