T3RU Test – Thyroid Hormone-Binding Ratio
Resin T3 uptake; T3 resin uptake; Thyroid hormone-binding ratio
The T3RU test measures the level of proteins that carry thyroid hormones in the blood. This can help your health care provider interpret the results of T3 and T4 blood tests.
Because tests called the free T4 blood test and TBG blood tests are now available, the T3RU test is rarely used these days.
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
Your provider will tell you if you need to stop taking any medicines before the test that may affect your test result. DO NOT stop taking any medicine without first talking to your provider.
Some drugs that can increase T3RU levels include:
- Anabolic steroids
- Heparin
- Phenytoin
- Salicylates (high dose)
- Warfarin
Some drugs that can decrease T3RU levels include:
- Antithyroid medicines
- Birth control pills
- Clofibrate
- Estrogen
- Thiazides
Pregnancy can also decrease T3RU levels.
These things can increase thyroxin binding globulin (TBG) levels (see below section “Why the Test is Performed” for more about TBG):
- Male hormones (androgens)
- Serious illness
- Kidney disease
Other medicines that bind to protein in the blood can also affect test results
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
This test is done to check your thyroid function. Thyroid function depends on the action of many different hormones, including thyroid-stimulating hormone (TSH), T3, and T4.
This test helps see how much thyroxin binding globulin (TBG) is available. TBG is a protein that carries most of the T3 and T4 in the blood.
Your provider may recommend a T3RU test if you have signs of a thyroid disorder, including:
- Hyperthyroidism (overactive thyroid)
- Hypothyroidism (underactive thyroid)
- Thyrotoxic periodic paralysis (muscle weakness caused by high levels of thyroid hormone in the blood)
Normal Results
Normal values range from 24% to 37%.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
Higher-than-normal levels may indicate:
- Kidney failure
- Overactive thyroid (hyperthyroidism)
- Nephrotic syndrome
- Protein malnutrition
- Acute hepatitis (liver disease)
- Pregnancy
- Hypothyroidism
- Use of estrogen
Abnormal results may also be due to an inherited condition of high TBG levels. Usually, thyroid function is normal in people with this condition.
This test may also be done for:
- Chronic thyroiditis (swelling or inflammation of the thyroid gland, including Hashimoto’s disease)
- Drug-induced hypothyroidism
- Graves disease
- Subacute thyroiditis
- Thyrotoxic periodic paralysis
- Toxic nodular goiter
Risks
Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
FAQ
What is the T3RU test?
- The T3RU test measures the level of proteins that carry thyroid hormones in the blood. This can help your health care provider interpret the results of T3 and T4 blood tests.
What is the normal value of T3RU?
- Normal values range from 24% to 37%. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What does a T3 uptake test show?
- The T3 resin uptake (T3RU) test is a test of thyroid-related proteins in the blood. 1 It’s used to help healthcare providers interpret the results of other thyroid tests, namely the T3 and T4 tests, which show how much thyroid hormone is available to the body in free form.
What is the TBG test?
- The TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. This protein is called thyroxine-binding globulin (TBG). Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand.
What can affect thyroid test results?
These are factors that can affect your thyroid levels:
- You get tested at different times of the day.
- You go to different labs for testing.
- You switch brands.
- You skip pills.
- You take the wrong dosage.
- You’re inconsistent.
- You become pregnant.
- You take other medications.
What are the symptoms of high T4 levels?
- Anxiety.
- Weight loss.
- Tremors in the hands.
- Increased heart rate.
- Puffiness.
- Bulging of the eyes.
- Trouble sleeping.
What does it mean if T3 uptake is high?
- If your results show high total T3 levels or high free T3 levels, it may mean you have hyperthyroidism. Low T3 levels may mean you have hypothyroidism, a condition in which your body doesn’t make enough thyroid hormone. T3 test results are often compared with T4 and TSH test results to help diagnose thyroid disease.
What are the symptoms of low T3?
Other possible symptoms include:
- weakness and fatigue.
- difficulty sleeping.
- increased sensitivity to heat or cold.
- weight loss or gain.
- dry or puffy skin.
- dry, irritated, puffy, or bulging eyes.
- hair loss.
- hand tremors.
What causes low T3 uptake?
- Low T3 levels.
- Depending on your situation, this can be the result of different medications, recent thyroid surgery, radiation therapy, pregnancy, or iodine deficiency. Another cause of hypothyroidism is Hashimoto’s thyroiditis, which is an autoimmune disorder where your immune system attacks your thyroid gland.
Does low T3 cause weight gain?
- Kitahara, if someone has low thyroid function, their TSH is high, and the thyroid hormones known as T3 and T4 are low—and weight gain often occurs.
What does high T uptake mean?
- A high T3 uptake means binding proteins are more saturated than normal. When combined with a total T4, this test allows the “free thyroid index” to be calculated, thus correcting for low or high thyroid-binding proteins.
What causes elevated TBG?
- Increased TBG levels may be due to hypothyroidism, liver disease, and pregnancy. Decreased TBG levels may be due to hyperthyroidism, renal disease, liver disease, severe systemic illness, Cushing syndrome, medications, and malnutrition.
Why is TBG important?
- Healthcare providers use the results of a TBG test to help them assess thyroid problems, including hypothyroidism (low thyroid hormone levels) and hyperthyroidism (high thyroid hormone levels), as well as to identify other conditions that may be altering the levels or activity of the thyroid hormones in your blood.
What is TBG concentration?
- The TBG concentration indicates whether an abnormally high or low total thyroid hormone concentration is offset by a parallel increase or decrease in TBG concentration. In TBG deficiency, one may find euthyroid patients with extremely low total thyroxine (T4) values.
What are early warning signs of thyroid problems?
Early Warning Signs of Thyroid Issues
- Fatigue.
- Weight gain.
- Weight loss.
- Slowed heart rate.
- Increased heart rate.
- Sensitivity to heat.
- Sensitivity to cold.
What are the symptoms of thyroid problems in females?
- Fatigue.
- Increased sensitivity to cold.
- Constipation.
- Dry skin.
- Weight gain.
- Puffy face.
- Hoarseness.
- Muscle weakness
Which time is best for a thyroid test?
- I recommend getting your thyroid function tests done first thing in the morning, bringing your medications with you, and taking them right after you have your thyroid function tests to ensure that you get accurate test results.
What happens if T4 is high?
- Elevated T4 levels may indicate hyperthyroidism. They may also indicate other thyroid problems, such as thyroiditis or toxic multinodular goiter. Other reasons for abnormal results may include high levels of protein in the blood.
What happens if you have too much T4?
- Hyperthyroidism (overactive thyroid) occurs when your thyroid gland produces too much of the hormone thyroxine. Hyperthyroidism can accelerate your body’s metabolism, causing unintentional weight loss and a rapid or irregular heartbeat.Nov 14, 2020
How do you treat high T4 levels?
- Antithyroid Medications: Antithyroid medications (sometimes written anti-thyroid) prevent the thyroid from producing excess amounts of T4 and T3 hormones. There are 2 types of antithyroid medications used in the US—propylthiouracil (PTU) and methimazole (also known as Tapazole).
What is a normal TSH level in a woman?
- In women, during the menstruation cycle, pregnancy, or after menopause, TSH levels may fall slightly outside the normal range, because of fluctuating levels of estrogen. The normal range of TSH levels in non-pregnant adult women is 0.5 to 5.0 mIU/L.
How do you fix low T3?
- Low T3 levels
- Sometimes, getting too much or too little iodine also causes symptoms. Treatment often includes levothyroxine medication, which replaces the hormones that the thyroid should produce.
How can I boost my T3?
- Selenium. Selenium is a trace element that is needed for the conversion of T4 to T3 so ensure that you eat selenium food sources daily to support this conversion and optimal levels. Sources include brazil nuts, walnuts, mushrooms avocados, fish, and cereal grains.
Should low T3 be treated?
- There is no evidence that treatment of patients with low T3 syndrome with thyroid hormones is of any benefit. Knowledge at the present moment suggests that the administration of thyroid hormones during caloric deprivation or non-thyroidal illness should be avoided.
What does it mean if TSH is normal but T3 is low?
- Subclinical hyperthyroidism is when you have low levels of TSH but have normal levels of T3 and T4. If you’re experiencing symptoms of subclinical hyperthyroidism, your doctor can use a series of blood tests to come to a diagnosis.
What is the best treatment for hyperthyroidism?
- Radioactive iodine is the most widely recommended permanent treatment of hyperthyroidism. This treatment takes advantage of the fact that thyroid cells are the only cells in the body that have the ability to absorb iodine.
What does it mean if T3 and T4 are normal but TSH is high?
- Thyroid Stimulating Hormone (TSH)
- When the thyroid gland becomes inefficient such as in early hypothyroidism, the TSH becomes elevated even though the T4 and T3 may still be within the “normal” range.
What is a critical TSH level?
- The standard reference range for the TSH level is anywhere between 0.30 and 5.0 IU/mL. If your TSH level is higher than 5.0 IU/mL, then the lab will flag you as “high,” and you may experience the symptoms listed above 5.0 uIU/mL. Values of the TSH level of more than 10.0 uIU/mL need long-term thyroid supplements.

Dr. MD Harun Ar Rashid, FCPS, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including FCPS, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and community outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices.