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Find a provider Request an appointment Our locations What is a TSH (thyroid stimulating hormone) Test?Definition: Alternative Names: Thyrotropin; Thyroid stimulating hormone How the test is performed: Adult or child: Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The tourniquet is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding. Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding. How to prepare for the test: How the test will feel: Why the test is performed: TRH, a hormone produced in the hypothalamus, stimulates the pituitary gland to release TSH. TSH subsequently stimulates the thyroid to produce thyroid hormones, T3 and T4. These hormones feedback to the hypothalamus and pituitary to regulate the release of both TSH and TRH. In certain diseases, this regulation pathway is altered, leading to under- or over-production of thyroid hormone. When a thyroid disorder is suspected clinically, a TSH level is obtained as an initial test. Normal Values: Some people with a TSH value over 2.0 mIU/L, who have no signs or symptoms suggestive of an under-active thyroid, may develop hypothyroidism sometime in the future. Anyone with a TSH above 2.0 mIU/L, therefore, should be followed very closely by a doctor. Note that each section in this article has a ‘summary’ box (like this one) to save time. Below this box is a contents menu to help you navigate directly to a particular section. Contents
What is TSH?It is actually produced by the brain’s pituitary gland, but stimulates production of the hormones triiodothyronine (T3) and thyroxine (T4) in the thyroid gland. The amount and balance of these hormones affects almost every physiological process in the body, particular your body’s metabolism (1).
What Makes TSH Fluctuate?The release of TSH is first stimulated by a hormone called TRH. Once the thyroid stimulating hormone makes its way to your thyroid, levels are largely dictated by the amount of T3 and T4 in your blood. When T3 and T4 levels are low, the body produces more TSH to stimulate the thyroid. But when T3 and T4 levels are high, the body produces less (2).
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Several other factors can also influence TSH levels:
Hypothyroidism: What is TSH Level?Due to the symbiotic nature they have with thyroid hormones, TSH levels in the blood can theoretically be a good marker of thyroid health. This TSH levels chart presents a simplified version of what different readings can indicate. TSH LevelsT3 and T4 LevelsDisease ConditionHighHighTumor of pituitary glandLowLowSecondary hypothyroidismLowHighGrave’s diseaseHighLowHashimoto’s diseaseThose with Graves’ disease (an overactive thyroid) have high low TSH and subsequent high thyroid hormone levels. Hashimoto’s disease (underactive thyroid) is the opposite.
Normal TSH levelsWhat should your TSH level be?Normal TSH levels for the average adult range from 0.4 ‑ 4.0 mIU/L (milli-international units per liter) (3). However, many organizations agree that a reading of 2.5 or less is truly ideal for normal thyroid levels, with anything 2.5 – 4.0 mIU/L considered “at risk”. For those on thyroxine, the ideal TSH normal range is between 0.5 to 2.5 mU/L. The reference ranges alter slightly as we grow older and if you are pregnant: TSH Normal Range By Age: For premature birth (28‑36 weeks)
For children
For adults
During pregnancy
Small variations in results can occur depending on the laboratory and its methods used, as well as the time of day your blood was taken.
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High TSH LevelsA level reading above 4.0 mIU/L is considered high (elevated). What is the reason for high TSH levels?High levels typically indicates an underactive thyroid gland, which produces too little thyroid hormone. This is known medically as hypothyroidism. Common causes of hypothyroidism include an autoimmune disease (known as Hashimoto’s disease), radiation treatment, or surgical removal of the thyroid gland. Replacing thyroid hormone and altering your diet are crucial for the safe and effective treatment of an underactive thyroid.
Low TSH levelsWhat does it mean when your TSH is low?Low levels typically indicates an overractive thyroid gland, which produces too much thyroid hormone. This is known medically as hyperthyroidism. It can be caused by an autoimmune disease (known as Graves’ disease), goiter, excessive iodine in the body, or an overdose of synthetic thyroid hormone. Initial hyperthyroidism treatment can involve anti‑thyroid medications and radioactive iodine to slow down thyroid hormone production. Most respond well to hyperthyroidism medications and are treated successfully.
The Problem With Solely Relying on TSH TestsIt has been the gold standard test for decades, and is considered the most sensitive and accurate indicator by most endocrinologists and other doctors. However, more recent research indicates our systematic reliance on it is missing the mark. This leaves a lot of hypothyroid cases either misdiagnosed or undiagnosed. Some clinical studies have found that both T3 and TSH levels can decline at the same time, particularly in obese individuals that lose weight (4, 5). That means T3 levels can be low, yet TSH will remain in the normal range. Certain medications, such as metformin, are also known to independently lower TSH levels in diabetics and PCOS patients with thyroid issues (6). These variables are just the tip of the iceberg, but highlight why TSH is not completely reliable on its own. Considering the pituitary gland (which produces TSH) is unique in its function, it makes sense that some metabolic processes and outside stressors can influence TSH activity. This is something to discuss with your doctor if your readings are high-normal, yet you still feel seriously unwell.
TSH Tests at HomeIt’s not uncommon for doctors to skip over TSH testing if they do not believe there is a thyroid issue. Fortunately, there is reliable way to measure thyroid stimulating hormones yourself with a home-testing kit. It’s FDA approved to be as accurate as a blood draw test, and results are sent direct to you by email or phone call. Have a read of the interesting reviews, as there’s the occasional comment that results are slow to get back. Additional Tests For Thyroid HealthGiven the potential inaccuracies with TSH on its own, comprehensive screening of thyroid health should ideally include these 6 tests: What is a normal TSH level in a woman?TSH normal values are 0.5 to 5.0 mIU/L. Pregnancy, a history of thyroid cancer, history of pituitary gland disease, and older age are some situations when TSH is optimally maintained in different range as guided by an endocrinologist.
What is considered a dangerously high TSH level in uIU mL?A TSH over 10 mIU/L has been linked to an increased risk of coronary heart disease and heart failure, which is why you'll probably want to seek treatment if your TSH is close to (but still under) that upper limit.
What is normal TSH level for age?
What is a good TSH blood level?A normal range for TSH in most laboratories is 0.4 milliunits per liter (mU/L) to 4.0 mU/L. If your TSH is higher than 4.0 mU/L on repeat tests, you probably have hypothyroidism. Your doctor may also order a T4 test.
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