Book Total T4 Test: Purpose, Normal Range and Price

The Total T4 test is a blood test that measures the total concentration of thyroxine in the blood, encompassing both the protein-bound and the free fractions of T4. Thyroxine is the primary hormone produced and secreted by the thyroid gland, a butterfly-shaped gland located in the front of the neck. T4 is produced in large quantities by the thyroid and serves as the main circulating thyroid hormone, with the majority being converted in peripheral tissues to the more biologically active T3. The thyroid gland's production of T4 is tightly regulated by TSH secreted by the pituitary gland, creating a feedback loop that maintains thyroid hormone levels within a narrow physiological range. The Total T4 test measures both bound T4, which is attached to carrier proteins including thyroxine-binding globulin, and free T4 combined. Because the bound fraction constitutes over 99% of total T4, conditions that alter binding protein levels including pregnancy, liver disease, oestrogen therapy, and certain medications can significantly affect total T4 results independent of actual thyroid function. For this reason, free T4 has largely replaced total T4 as the preferred thyroid hormone measurement in modern clinical practice. However, total T4 remains clinically useful in specific situations including neonatal thyroid screening, monitoring thyroid hormone replacement in certain patient groups, and in settings where free T4 assays are unavailable. The test involves a simple blood draw completed in under five minutes

Doctors prescribe a Total T4 test in the following situations: Evaluating thyroid function as part of a thyroid profile alongside TSH in patients with symptoms of hypothyroidism including fatigue, weight gain, cold intolerance, constipation, and dry skin, or hyperthyroidism including palpitations, weight loss, tremor, and heat intolerance. Neonatal thyroid screening in newborns where total T4 alongside TSH is used to screen for congenital hypothyroidism, a condition requiring immediate treatment to prevent permanent intellectual disability and growth retardation in affected infants. Monitoring thyroid hormone replacement therapy with levothyroxine in patients with hypothyroidism where total T4 alongside TSH tracks whether the prescribed dose is maintaining thyroid hormone levels within the therapeutic range. Evaluating patients with abnormal thyroxine-binding globulin levels including those on oestrogen therapy, oral contraceptive pills, and during pregnancy where total T4 is elevated due to increased binding protein rather than true thyroid overactivity, and must be distinguished from genuine hyperthyroidism. Investigating suspected thyroid disorders in settings or clinical contexts where total T4 provides additional information alongside TSH and free T4 to complete the thyroid function assessment and guide specialist evaluation. Screening for thyroid dysfunction in patients with metabolic disorders, dyslipidaemia, unexplained anaemia, menstrual irregularities, and infertility where thyroid disease is a common and frequently overlooked contributing factor.

The Total T4 test measures the combined concentration of bound and free thyroxine in the blood, reported in micrograms per decilitre (mcg/dL) or nanomoles per litre (nmol/L). Normal Total T4 Range in India The standard reference ranges used across most Indian diagnostic laboratories are as follows. For adults, a normal Total T4 level is between 5.0 and 12.0 mcg/dL or 64 to 154 nmol/L. In neonates and children, normal ranges are higher than adults due to physiologically elevated thyroid activity during growth and development. Reference ranges may vary slightly between laboratories. Interpreting Total T4 Results A low Total T4 below 5.0 mcg/dL alongside an elevated TSH confirms hypothyroidism. The degree of T4 suppression reflects the severity of thyroid underfunction and guides the initial levothyroxine dose required to restore normal thyroid hormone levels. An elevated Total T4 above 12.0 mcg/dL requires careful interpretation as the elevation may reflect true hyperthyroidism with excessive thyroid hormone production or simply an increase in thyroxine-binding globulin due to pregnancy, oestrogen therapy, or liver disease that raises bound T4 without genuine thyroid overactivity. Free T4 measurement resolves this distinction when clinically necessary. A Total T4 in the normal range alongside an abnormal TSH may indicate subclinical thyroid dysfunction where TSH is already responding to early thyroid underperformance or overactivity before T4 has moved outside the reference range, which is why TSH is always the preferred first-line thyroid screening test.

No fasting is strictly required for the Total T4 test alone. However if Total T4 is part of a broader hormonal or metabolic panel that includes fasting parameters, fast as advised by your doctor. Our team confirms preparation requirements at the time of booking. Collect the sample ideally in the morning as thyroid hormones show mild diurnal variation. This is particularly relevant when Total T4 is being used to monitor levothyroxine replacement therapy. Inform the phlebotomist about all thyroid medications you are currently taking. If you are on levothyroxine, do not take your morning dose before the blood test as post-absorption spikes transiently raise T4 and do not reflect your true steady-state level. Take levothyroxine after the blood draw. Inform your doctor about all medications including oestrogens, oral contraceptive pills, androgens, corticosteroids, amiodarone, lithium, phenytoin, and biotin supplements as all of these can affect thyroxine-binding globulin levels or thyroid function and must be disclosed for accurate interpretation. Stay normally hydrated before sample collection.

If you are booking through the SecondMedic platform the Total T4 test price starts at approximately Rs. 231. The exact price will be confirmed at the time of booking through SecondMedic. If your doctor has prescribed multiple tests alongside Total T4, SecondMedic health packages include Total T4 as part of a broader thyroid function or endocrine panel at a significantly lower combined price.

SecondMedic provides home sample collection for Total T4 test across all major areas. You do not need to visit a lab or collection centre. A certified and trained phlebotomist comes to your home or workplace at your chosen time, collects the sample using sterile single-use equipment, and ensures it is transported to the NABL-accredited lab within the required time window for accurate processing. Please note that SecondMedic provides free home sample collection on all tests priced above Rs. 300. Our team will check your pincode and confirm if your address falls under our free sample collection eligibility criteria, which depends upon the lab location and phlebotomist availability. Home collection is available between 7 AM and 10 PM, seven days a week, including Sundays and public holidays. If you are on levothyroxine, book the earliest available morning slot and take your medication only after the blood draw. Enter your pincode on the booking page or call our helpline to confirm availability at your address.