BACK TOTOP Browse A-ZSearchBrowse A-ZABCDEFGHIJKLMNOPQRSTUVWXYZ0-9 E-mail FormEmail ResultsName:Email address:Recipients Name:Recipients address:Message: Print-FriendlyBookmarksbookmarks-menuT3RU testResin T3 uptake; T3 resin uptake; Thyroid hormone-binding ratioThe T3RU test measures the level of proteins that carry thyroid hormone in the blood. This can help your health care provider interpret the results of T3 and T4 blood tests. T3Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body's control of metabolism (the many processes that control the rate...ImageRead Article Now Book Mark Article T4T4 (thyroxine) is the main hormone produced by the thyroid gland. A laboratory test can be done to measure the amount of free T4 in your blood. Fre...ImageRead Article Now Book Mark Article Because tests called the free T4 blood test and thyroxine binding globulin (TBG) blood tests are now available, the T3RU test is rarely used these days.Thyroxine binding globulinThe TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. This protein is called thyroxine-binding globuli...ImageRead Article Now Book Mark Article How the Test is Performed A blood sample is needed. Blood sampleVenipuncture is the collection of blood from a vein. It is most often done for laboratory testing.ImageRead Article Now Book Mark Article 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 medicines that can increase T3RU levels include:Anabolic steroids Heparin Phenytoin Salicylates (high dose) Warfarin Some medicines that can decrease T3RU levels include:Antithyroid medicines Birth control pills Estrogen Thiazides Opioids and methadonePregnancy can also decrease T3RU levels.These conditions can decrease TBG levels (see below section Why the Test is Performed for more about TBG):Serious illness Kidney disease when protein is lost in the urine (nephrotic syndrome)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 check the amount of T3 that TBG is able to bind. 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: Overactive thyroid (hyperthyroidism) HyperthyroidismHyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often called overactive thyroid.ImageRead Article Now Book Mark Article Underactive thyroid (hypothyroidism) HypothyroidismHypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This condition is often called underactive thyroid....ImageRead Article Now Book Mark Article Muscle weakness caused by high levels of thyroid hormone in the blood (thyrotoxic periodic paralysis) Thyrotoxic periodic paralysisThyrotoxic periodic paralysis (TPP) is a condition with episodes of severe muscle weakness. It occurs in people who have high levels of thyroid horm...ImageRead Article Now Book Mark Article Normal Results Normal values range from 25% to 38%.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 Kidney failureAcute kidney failure is the rapid (less than 2 days) loss of your kidneys' ability to remove waste and help balance fluids and electrolytes in your b...ImageRead Article Now Book Mark Article Overactive thyroid (hyperthyroidism) Nephrotic syndrome Nephrotic syndromeNephrotic syndrome is a group of symptoms and abnormal test results that include protein in the urine, low blood protein levels in the blood, high ch...ImageRead Article Now Book Mark Article Protein malnutrition Protein malnutritionKwashiorkor is a form of malnutrition that occurs when there is not enough protein in the diet.ImageRead Article Now Book Mark Article Chronic liver diseaseLower-than-normal levels may indicate:Acute hepatitis (liver disease) HepatitisHepatitis is swelling and inflammation of the liver.ImageRead Article Now Book Mark Article Pregnancy Hypothyroidism Use of estrogen, opioids or methadoneAbnormal 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 disease) Chronic thyroiditisChronic thyroiditis is caused by a reaction of the immune system against the thyroid gland. It often results in reduced thyroid function (hypothyroi...ImageRead Article Now Book Mark Article Drug-induced hypothyroidism Graves disease Graves diseaseGraves disease is an autoimmune disorder that leads to an overactive thyroid gland (hyperthyroidism). An autoimmune disorder is a condition that occ...ImageRead Article Now Book Mark Article Subacute thyroiditis Subacute thyroiditisSubacute thyroiditis is an immune reaction of the thyroid gland that often follows an upper respiratory infection. The thyroid gland is located in th...ImageRead Article Now Book Mark Article Thyrotoxic periodic paralysis Toxic nodular goiterToxic nodular goiterToxic nodular goiter involves an enlarged thyroid gland. The gland contains areas that have increased in size and formed nodules. One or more of th...ImageRead Article Now Book Mark Article Risks There is little risk involved with having your blood taken. 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 Multiple punctures to locate veins Blood buildup under the skin (hematoma) HematomaA bruise is an area of skin discoloration. A bruise occurs when small blood vessels break and leak their contents into the soft tissue beneath the s...ImageRead Article Now Book Mark Article Infection (a slight risk any time the skin is broken)Open ReferencesReferencesFaix JD. Thyroid function testing (thyrotropin, triiodothyronine, and thyroxine). In: Robertson RP, ed. DeGroot's Endocrinology. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 68.Guber HA, Oprea M, Rusell YX. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 25.Pearce EN, Hollenberg AN. Thyroid. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 207.Salvatore D, Cohen R, Kopp PA, Larsen PR. Thyroid pathophysiology and diagnostic evaluation. In: Melmed S, Auchus RJ, Golfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 11.Wassner AJ, Smith JR. Thyroid development and physiology. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 601.AllVideoImagesTogBlood test - illustration Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.Blood testillustrationBlood test - illustration Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.Blood testillustration Tests for T3RU test T3RU testRelated Information Free T4 test(Medical Test)Protein in diet(Nutrition)T3 test(Medical Test)Hyperthyroidism(Condition)Nephrotic syndrome(Condition)Kwashiorkor(Condition)Acute kidney failure(Condition)Hepatitis B(Condition)Hypothyroidism(Condition)Chronic thyroiditis (Hashimoto disease)(Condition)Hepatitis - InDepth(In-Depth)Hypothyroidism - InDepth(In-Depth) Review Date: 2/28/2024 Reviewed By: Sandeep K. Dhaliwal, MD, board-certified in Diabetes, Endocrinology, and Metabolism, Springfield, VA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. 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T3RU testResin T3 uptake; T3 resin uptake; Thyroid hormone-binding ratioThe T3RU test measures the level of proteins that carry thyroid hormone in the blood. This can help your health care provider interpret the results of T3 and T4 blood tests. T3Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body's control of metabolism (the many processes that control the rate...ImageRead Article Now Book Mark Article T4T4 (thyroxine) is the main hormone produced by the thyroid gland. A laboratory test can be done to measure the amount of free T4 in your blood. Fre...ImageRead Article Now Book Mark Article Because tests called the free T4 blood test and thyroxine binding globulin (TBG) blood tests are now available, the T3RU test is rarely used these days.Thyroxine binding globulinThe TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. This protein is called thyroxine-binding globuli...ImageRead Article Now Book Mark Article How the Test is Performed A blood sample is needed. Blood sampleVenipuncture is the collection of blood from a vein. It is most often done for laboratory testing.ImageRead Article Now Book Mark Article 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 medicines that can increase T3RU levels include:Anabolic steroids Heparin Phenytoin Salicylates (high dose) Warfarin Some medicines that can decrease T3RU levels include:Antithyroid medicines Birth control pills Estrogen Thiazides Opioids and methadonePregnancy can also decrease T3RU levels.These conditions can decrease TBG levels (see below section Why the Test is Performed for more about TBG):Serious illness Kidney disease when protein is lost in the urine (nephrotic syndrome)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 check the amount of T3 that TBG is able to bind. 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: Overactive thyroid (hyperthyroidism) HyperthyroidismHyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often called overactive thyroid.ImageRead Article Now Book Mark Article Underactive thyroid (hypothyroidism) HypothyroidismHypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This condition is often called underactive thyroid....ImageRead Article Now Book Mark Article Muscle weakness caused by high levels of thyroid hormone in the blood (thyrotoxic periodic paralysis) Thyrotoxic periodic paralysisThyrotoxic periodic paralysis (TPP) is a condition with episodes of severe muscle weakness. It occurs in people who have high levels of thyroid horm...ImageRead Article Now Book Mark Article Normal Results Normal values range from 25% to 38%.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 Kidney failureAcute kidney failure is the rapid (less than 2 days) loss of your kidneys' ability to remove waste and help balance fluids and electrolytes in your b...ImageRead Article Now Book Mark Article Overactive thyroid (hyperthyroidism) Nephrotic syndrome Nephrotic syndromeNephrotic syndrome is a group of symptoms and abnormal test results that include protein in the urine, low blood protein levels in the blood, high ch...ImageRead Article Now Book Mark Article Protein malnutrition Protein malnutritionKwashiorkor is a form of malnutrition that occurs when there is not enough protein in the diet.ImageRead Article Now Book Mark Article Chronic liver diseaseLower-than-normal levels may indicate:Acute hepatitis (liver disease) HepatitisHepatitis is swelling and inflammation of the liver.ImageRead Article Now Book Mark Article Pregnancy Hypothyroidism Use of estrogen, opioids or methadoneAbnormal 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 disease) Chronic thyroiditisChronic thyroiditis is caused by a reaction of the immune system against the thyroid gland. It often results in reduced thyroid function (hypothyroi...ImageRead Article Now Book Mark Article Drug-induced hypothyroidism Graves disease Graves diseaseGraves disease is an autoimmune disorder that leads to an overactive thyroid gland (hyperthyroidism). An autoimmune disorder is a condition that occ...ImageRead Article Now Book Mark Article Subacute thyroiditis Subacute thyroiditisSubacute thyroiditis is an immune reaction of the thyroid gland that often follows an upper respiratory infection. The thyroid gland is located in th...ImageRead Article Now Book Mark Article Thyrotoxic periodic paralysis Toxic nodular goiterToxic nodular goiterToxic nodular goiter involves an enlarged thyroid gland. The gland contains areas that have increased in size and formed nodules. One or more of th...ImageRead Article Now Book Mark Article Risks There is little risk involved with having your blood taken. 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 Multiple punctures to locate veins Blood buildup under the skin (hematoma) HematomaA bruise is an area of skin discoloration. A bruise occurs when small blood vessels break and leak their contents into the soft tissue beneath the s...ImageRead Article Now Book Mark Article Infection (a slight risk any time the skin is broken)Open ReferencesReferencesFaix JD. Thyroid function testing (thyrotropin, triiodothyronine, and thyroxine). In: Robertson RP, ed. DeGroot's Endocrinology. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 68.Guber HA, Oprea M, Rusell YX. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 25.Pearce EN, Hollenberg AN. Thyroid. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 207.Salvatore D, Cohen R, Kopp PA, Larsen PR. Thyroid pathophysiology and diagnostic evaluation. In: Melmed S, Auchus RJ, Golfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 11.Wassner AJ, Smith JR. Thyroid development and physiology. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 601.