T4 (thyroxine) total test
Quick answer: A total T4 test measures thyroxine, the main hormone made by the thyroid gland, in your blood. It is ordered with TSH to look for an overactive or underactive thyroid and to monitor treatment.
- SampleBlood
- TakesAbout 5 minutes
- Before the testNo special preparation is usually needed.
- In fertility careThyroid problems can affect periods, ovulation and pregnancy, so thyroid tests are common in fertility care.
How the test is done
- 1Your arm is cleaned and a tourniquet is applied
- 2Blood is drawn into a tube, often with TSH
- 3The tourniquet is released and a plaster is applied
- 4The lab measures total T4 in the sample
What your results can mean
Reading your report
Pregnancy and hormone tablets raise total T4, so read it with your TSH and discuss it with your doctor.
If the result is outside the usual range
A high total T4 can be seen with an overactive thyroid, and also with pregnancy or oestrogen-containing pills, which raise the protein that carries T4. A low total T4 can be seen with an underactive thyroid or when the carrier protein is low.
Who usually has this test
People with symptoms of thyroid disease, and those on thyroid treatment, usually tested alongside TSH.
Risks and aftercare
You can take your thyroid tablet after the sample if your doctor advised waiting.
Names and options
Also called: total T4, T4 test, thyroxine
Listed by the hospital as
- T4 (THYROXINE) TOTAL, SERUM
Questions about this test
What is the difference between total T4 and free T4?
Total T4 includes hormone bound to proteins, while free T4 measures only the active hormone. Free T4 is more often used, especially in pregnancy, because it is less affected by changes in carrier proteins.
Why does pregnancy raise total T4?
In pregnancy, oestrogen raises the protein that carries T4, so total T4 goes up even when the thyroid is working normally. Doctors use pregnancy-specific targets and often prefer free T4 or TSH.
Should I take my thyroxine tablet before a T4 test?
Thyroxine can raise T4 for a few hours after a dose. Ask your doctor whether to take your tablet after the sample on the test day.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
Get directions ↗IVF Pulse fertility care at Tamara Hospital →
Reception
Waiting area
IVF lab
This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.