The TSH Reference Range: A Guide for Thyroid Patients

Everything You Need to Know About Thyroid Stimulating Hormone Tests

Doctor taking blood sample of a man
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The thyroid stimulating hormone test—also known as the TSH test—is the key test used by conventional physicians in diagnosis and treatment of thyroid disease. It’s essential that as a thyroid patient, you understand this test, the meaning of your results, and the controversies that surround the TSH reference range.

What is the TSH Test?

The TSH test measures thyroid stimulating hormone or TSH. TSH is a hormone is released by your pituitary gland in response to the levels of thyroid hormone in your bloodstream.

When low levels of thyroid hormone are detected, the pituitary releases more TSH to encourage your thyroid gland to produce more hormone. When too much thyroid hormone is detected, the pituitary slows down the production of TSH.

The TSH test is the first-line blood test used to diagnose thyroid disease and manage thyroid treatment. At the most basic level, elevated levels of TSH are considered evidence of hypothyroidism, an underactive thyroid. Low levels of TSH are considered evidence of hyperthyroidism, an overactive thyroid.

What Is a Reference Range / TSH Reference Range?

A reference range is obtained by taking a large group of people in the population, running a particular test, calculating the values, and creating a range that is supposed to represent the “normal” levels of people who are free of a particular disease or abnormality.

The TSH reference range represents a range of TSH levels of people who are supposedly free of thyroid disease and who have normal thyroid function.

Currently, at most laboratories in the U.S., the reference range for TSH tests is approximately 0.5 to 5.0 mU/l. Depending on the lab, you may seem some variations, i.e., 0.4 to 5.5 mU/l, or 0.6 to 4.5 mU/l, etc., but generally, 0.5 to 5.0 mU/l is considered typical of many labs.

Typically, your doctor will interpret a level below 0.5 mU/l as indicative of hyperthyroidism (an overactive thyroid), and a level above 5.0 mU/l as indicative of hypothyroidism (an underactive thyroid.)

The following chart shows a typical laboratory TSH reference range:

       TSH Reference Range                           Interpretation
  0.5 to 5.0 mU/l  - Level below 0.5 mU/l indicative of
  hyperthyroidism
  - Level above 5.0 mU/l indicative of
  hypothyroidism 


The TSH Reference Range Controversy

The actual TSH reference range has been controversial for more than a decade. Back in 2003, after evidence showed that patients who had TSH levels in the higher end of the TSH reference range tended to go on to develop hypothyroidism more often than those in the lower end of the range, the American Association of Clinical Endocrinologists (AACE) recommended that doctors "consider treatment for patients who test outside the boundaries of a narrower margin based on a target TSH level of 0.3 to 3.0 mU/l. At the time, AACE believed that the new range would “result in proper diagnosis for millions of Americans who suffer from a mild thyroid disorder, but have gone untreated."

According to AACE’s president Hossein Gharib, MD,

The prevalence of undiagnosed thyroid disease in the United States is shockingly high...The new TSH range from the AACE guidelines gives physicians the information they need to diagnose mild thyroid disease before it can lead to more serious effects on a patient's health, such as elevated cholesterol, heart disease, osteoporosis, infertility, and depression."

At the time, the announcement from AACE was seen by many as a long-overdue and much-needed improvement for patients.

Unfortunately, what was considered a very positive development for thyroid patients did not make a significant impact, for several reasons: 

  • Laboratories never adopted the new range as the formal reference range, meaning that only levels outside the older, broader range were flagged as abnormal.
  • The medical establishment continued to disagree about the TSH reference range, as evidenced by two prominent articles that appeared in the September 2005 issue of Journal of Clinical Endocrinology and Metabolism, presenting the two sides of the argument.

    Doctors Martin Surks, Gayotri Goswami and Gilbert Daniels argued that the reference range should remain the same in their article "Controversy in Clinical Endocrinology: The Thyrotropin Reference Range Should Remain Unchanged." They based their argument on their assertion that "because routine levothyroxine treatment is not recommended for subclinical hypothyroidism, it is certainly not warranted in individuals with upper reference range TSH” levels of 2.5 to 4.5 mU/l.

    Doctors Leonard Wartofsky and Richard Dickey argued in their article, "The Evidence for a Narrower Thyrotropin Reference Range is Compelling," that the previously accepted reference ranges are no longer valid because the reference populations previously considered normal were "contaminated" with individuals with various levels of thyroid disease. They argued that the benefits of treatment far outweigh any minimal risks.

    Doctors Wartofsky and Dickey defended the shift to the new range, saying:

    We will probably never have an absolutely cutoff value for TSH distinguishing normal from abnormal, but recognition that the mean of normal TSH values is only between 1.18 and 1.4 mU/l and that more than 95% of the normal population will have a TSH level less than 2.5 mU/l clearly imply that anyone with a higher value should be carefully assessed for early thyroid failure.

    By 2006, the endocrinology groups abandoned the recommendation to broaden the TSH reference range, Still, the back-and-forth debate has continued for more than a decade, and as of 2017, the controversy continues. Still, the vast majority of conventional healthcare practitioners are instructed to use the broader TSH reference range in diagnosing and treating thyroid patients.  

    If Your TSH is Normal, Could You Still Be Hypothyroid?

    It is important for thyroid patients to know that research has shown that:

    • In an iodine-sufficient population, the mean TSH is 1.5 mU/l
    • In studies of population groups with a low incidence of Hashimoto's thyroiditis, the mean TSH is 1.18 mU/l
    • When people with positive antithyroid antibodies or a family history of autoimmune thyroid disease are excluded from the reference range calculations, the normal reference range runs from around .4 to 2.5 mU/l
    • During pregnancy, guidelines state that TSH levels should never rise above 3.0, in order to protect the health of both mother and baby.
    • TSH levels in the higher end of the reference range are also linked to increased risks of thyroid cancer, elevated cholesterol, infertility, heart disease, type 2 diabetes, and a number of other health issues.
    • TSH levels tend to be higher earlier in the day. A TSH test done later in the day could show your levels as within the reference range, while an earlier morning test might show hypothyroidism. 

    If your TSH test result falls within the reference range and you’re told “your TSH is normal,” could you still be hypothyroid? Many conventional physicians say no, and many integrative and holistic practitioners say yes. Whether you can be hypothyroid with a normal TSH level ultimately remains a controversial issue.

    A Word from Verywell

    As you’ve learned, the definition of a "normal" TSH level depends on the doctor you're consulting and his or her ideas about thyroid disease. At the same time, the TSH test and TSH reference range are crucial to your thyroid health and treatment. As a result, there are some important things to keep in mind.

    1. You need to ask what TSH level your doctor is targeting for you, and why. You may have a doctor who believes that keeping you at the top of the range is the sole objective or one who is focusing on a lower TSH and relief of your symptoms. (Also, doctors target very low or suppressive TSH levels for some thyroid cancer survivors, as a way to prevent cancer recurrence.) The majority of doctors, however, are still using the TSH reference range of around 0.5 to 5.0 for diagnosis and management of your thyroid disease.

    2. You should not accept the answers "normal," "high," or "low" as a report on your blood tests. Instead, ask for the actual numbers and ask for the laboratory’s reference range. Even better yet, ask for a copy of the actual blood test results.

    3. If your TSH test levels are within the reference range, and you have symptoms consistent with hypothyroidism, you may want to request additional tests to aid in a more thorough diagnosis. While conventional physicians frequently rely on the TSH test alone, some physicians also measure the actual thyroid hormones—thyroxine (T4) and triiodothyronine (T3)—as well as thyroid antibody levels and reverse T3. These doctors are looking for additional measurements to make a diagnosis. For example, when your T4 and T3 hormone levels are low, hypothyroidism is suspected, and when they are high, hyperthyroidism is suspected.

    Antibodies—especially thyroid peroxidase (TPO) antibodies that can diagnose Hashimoto’s disease—are also sometimes measured. A subset of practitioners believes that a thyroid gland that is in the process of autoimmune failure—as evidenced by elevated TPO antibody levels—can cause hypothyroidism symptoms long before the hypothyroidism is reflected in the TSH, or even Free T4 and Free T3, tests. They also believe that treatment with thyroid hormone replacement drugs may help relieve your symptoms, lower your antibody levels, and prevent you from becoming overtly hypothyroid.

    4. If your TSH test levels fall at the higher end of the reference range, and you have symptoms consistent with hypothyroidism, consider discussing a therapeutic trial of thyroid hormone replacement with your physician.

    5. If your doctor refuses to run additional tests or refuses to treat you, consider finding a new doctor for your thyroid care. Integrative and holistic physicians often include many tests in addition to the TSH test, and take your medical history and symptoms into account, with the goal of finding a safe and optimal TSH that will safely relieve your symptoms.

    Sources:

    Anderson et. al., "Narrow Individual Variations in the Serum T4 and T3 in Normal Subjects: A Clue to the Understanding of Subclinical Thyroid Disease," Journal of Clinical Endocrinology and Metabolism, 87(3): 1068-1072

    Garber J, Cobin R, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: Cosponsored by the American association of clinical endocrinologists and the American thyroid association. Endocrine Practice. 2012;18(6):988–1028. doi:10.4158/ep12280.gl.

    Guber HA, Farag AF. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 24.

    Surks, et.al. "Controversy in Clinical Endocrinology: The Thyrotropin Reference Range Should Remain Unchanged," Journal of Clinical Endocrinology and Metabolism 90(9)/5489-5496

    Wartofsky & Dickey, "Controversy in Clinical Endocrinology: The Evidence for a Narrower Thyrotropin Reference Range is Compelling," Journal of Clinical Endocrinology and Metabolism  

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