Total T3 in Dehradun

What is a Total T3?

T3, triiodothyronine, is the more biologically active of the two thyroid hormones. The thyroid actually secretes mostly T4, and the body converts it into T3 in the liver, kidney and other tissues as demand requires, so T3 represents the hormone at the point of action rather than at the point of manufacture. Total T3 measures all of it, both the small free fraction that is active and the much larger portion bound to carrier proteins. That is the measurement's main limitation, because anything that changes carrier-protein levels changes the total without changing thyroid function at all: pregnancy, the contraceptive pill, oestrogen therapy and liver disease all raise it, while serious illness and some medicines lower it. T3 is at its most useful in suspected overactivity, where it often rises earlier and more steeply than T4, and in a specific pattern called T3 toxicosis, in which TSH is suppressed and T4 is still normal but T3 is clearly high. It is a poor test for underactivity, because the body preserves T3 production until hypothyroidism is well established, so a normal T3 does not rule it out.

Why take this test?

A T3 test is advised where an overactive thyroid is suspected: a fast or irregular heartbeat, palpitations, weight loss despite a good appetite, tremor of the hands, heat intolerance and excessive sweating, anxiety, irritability, difficulty sleeping, or loose stools. It is ordered when TSH comes back suppressed, to establish how overactive the gland is and to detect T3 toxicosis, and it is used to monitor treatment with anti-thyroid medicines. It is a routine component of a full thyroid profile alongside T4 and TSH, which is how most people encounter it. It is much less informative as a screening test on its own; for anyone simply checking their thyroid, TSH is the right first step, and T3 is added when the clinical picture or the TSH result calls for it.

• Fast or irregular heartbeat, or palpitations
• Weight loss despite a normal or increased appetite
• Hand tremor, heat intolerance or excessive sweating
• Anxiety, irritability or difficulty sleeping
• A suppressed TSH needing to be graded
• Monitoring treatment with anti-thyroid medicines

Normal reference ranges

Ranges are indicative for adults. Your report carries the lab-specific reference range and is reviewed by a LabONE pathologist; always interpret results with your doctor.

FAQs: Total T3 in Dehradun