Blood tests are the easiest and the fastest way for the doctor to assess your hormonal balance and health. Thyroid function tests are one of the most common lab tests, and most of the times, they will clearly show if the thyroid is underactive. However, in some cases, it may happen the test results are confusing. How can the same “normal” range fit almost any person of any age, gender, and physical constitution?

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What Is Normal?

Normal ranges were created by people a long time ago, in order to help understand and classify health and illness. It was of tremendous help at that point, when some cut-offs needed to be made and diseases were studied mostly in their most severe (read: deadly) forms. Today is different, we are heading towards personalisation in every aspect of life, and health is a major part of our lives. We need to step into the gray zone.

Dr. Vedrana Högqvist Tabor, Guest
Thyroid Nation
TSH test is a first step towards the diagnosis of hypothyroidism. However it can be very misleading... Click To Tweet

Is The Normal Value The Same For Everyone?

No, it is not.

What is normal for you, might not be normal for the person next to you. Also, what is normal for you today will likely not be normal for you in the future. Your weight, stress levels or dietary habits might change, you might get pregnant, relocate and more. That, plus your genes will determine your normal values for any given moment in your life.

What Does It Mean To Have A Blood Value Out Of Range?

Medically accepted averages vary from country to country. I know this so well, I lived in four different countries and had to think hard if I belonged to southeastern Europe because my origins are from there, or did the northern exposure in Sweden change my “normal” values too. Keep this in your mind if you are relocating.

Scientist in me screams: one measurement at one point in time will not tell you much. You should re-test one or two times to make sure your blood values are true. This way you and your healthcare practitioner can actually get a good picture of your health.

TSH test is a first step towards the diagnosis of hypothyroidism. However it can be very misleading, it is shown to increase with aging, and is not an immediate sign of disease [1].

The same is known for babies, when born and growing up they have high TSH values, which drop as they reach puberty [1].

Are You Safe If You Have A Value Inside The Average Range? 

In general, yes, but not always.

You should observe if the value is shifting from one end of the “normal” range to the other. Even shifts as this might be normal, caused by stress, seasonal changes, other illness, changes in the lifestyle, change in your current medications. Some patients at the first stage of Hashimoto’s have TSH levels which are by some lab’s considered normal 2.5–4.5 mIU/L [1]. The best advice? Know yourself and know your body.

What Might Tamper With Test Results?

  1. The time of the day, the time of the year.

TSH is not produced by the thyroid at the equal rate during the entire day. It follows a circadian rhythm and is mostly produced during our sleep.

Presently a normal reference range of serum TSH for adults is 0.4–4.5mIU/L.

In some countries that upper limit has been disputed, and reduced to 2.5mIU/L [2].

  1. Type of the test used.
  2. Eating too little or overeating.

If you are undernourished you might experience the decrease in fT3 and total T3. Overeating will have an opposite effect and increase fT3 and T3

  1. Stress

Stress is a big factor in thyroid health, and it decreases T3.

  1. Certain medications

Medications can increase fT3 and fT4, but not really in a good way. These medications block the activity of T3 and T4, so it does not matter if more of T3 and T4 can be found in the blood. They are unable to fulfil their role.

  1. Exercise

Basically, if you have just run a marathon, or did any type of long, excessive or high-intensity exercise, wait for a couple of days before going to be tested. And, in general it is good not to overexercise yourself if you have a thyroid condition.

  1. Sometimes labs make mistakes too.

It is not often, but people work in labs, and us people make mistakes. Sometimes the chemicals used for testing might be old or spoiled, I worked in the lab, it can happen. Luckily, people in the lab realize that very fast and can re-test with the same blood sample and freshly prepared chemicals 🙂

What Do Thyroid Antibodies Tell Us?

Three antibodies related to autoimmune thyroid disease can tell what type of autoimmune disease one has, and how severe or advanced it might be.

Anti-thyroglobulin (TgAb), anti-thyroperoxidase (TPOAb) and anti-TSH receptor (TRAb)

High levels of TgAb are present in 8 in 10 patients with Hashimoto’s and in 4 in 10 of people being diagnosed with Grave’s disease.

High levels of TPOAb are found in 9 in 10 patients with Hashimoto’s and 8 in 10 of patients with Grave’s disease.

High levels of either TgAb or TPOAb can be found in 1 in 10 of people without autoimmune thyroid disease, as well as in 2 in 10 of people that are deemed healthy.

High levels of TRAb are found in 9 in 10 patients with Grave’s disease and in less than 2 in 10 patients with Hashimoto’s.

Equally, it seems that in a small group of people with autoimmune diseases, no antibodies are detected.

TPOAb testing in early pregnancy can predict if a person is under the risk of developing postpartum thyroiditis. Postpartum thyroiditis occurs in about 1 in 10 people after giving birth. About 5 in 10 of pregnant people with high TPOAb will develop postpartum thyroiditis [1].

TgAb or TPOAb were found in 1 in 10 healthy people, more in females than males, and more in elderly [3, 4].

How Do TSH Values Change With Age?

Newborns And Young Children

TSH and T4 levels are high in newborn babies, as the baby grows the levels start dropping. T3 increases during the first year of life, but then it starts dropping [8].


TSH and T4 are decreasing and will reach expected adult levels at around 18 years old [8].


Several studies done on more than 10,000 non-diagnosed people show that for a healthy population TSH value is close to 1.5 mIU/L, and is higher in females than in males.

1 in 10 adults under 30 years have TSH higher than 2.5mIU/liter [5].


TSH levels rapidly grow during pregnancy. They increase from the average 1.20 mIU/L in the first trimester to 2.12 mIU/L in the second and 3.30 mIU/L in the third trimester. The range of T3 is 1.7–4.3 nmol/L in the second trimester and 0.4–3.9 nmol/L in the third trimester. T4 range is 92.2–252.8 nmol/L in the second trimester and 108.2–219.0 nmol/L in the third trimester [7].


4 in 10 people over 80 years have TSH higher than 2.5mIU/liter, and 1 in 10 has TSH higher than 4.5mIU/liter [5].

Some research suggests that the upper normal TSH reference range in people over 70 years old should be extended to 6.0 mIU/L [6]. A study on more than 15,000 people in Scotland has confirmed that the TSH values should be reconsidered for different age intervals, and especially in people older than 70 years should not be considered out of normal ranges [10].

Is TSH Over 2.5 Indicative Of A Disease?


1 in 10 of people with TSH values above 3.0 mIU/L has Hashimoto’s [9].

TSH itself, as a marker of disease, is not enough. If you have any symptoms connected to a thyroid, talk to your health provider and get the full thyroid blood work done. This is the best first step towards understanding the health of your thyroid.

Mildly Hypothyroid, Subclinical Hypothyroid And Hypothyroid: What’s The Difference?

There is a big difference between the subclinical, mildly hypothyroid and (overtly) hypothyroid. It will determine the treatment options you will be offered.

In most cases, doctors will wait with prescribing thyroid therapy until the patient is overtly hypothyroid. Symptoms will in most of the cases become stronger as hypothyroidism intensifies.

However, even the mild hypothyroidism is significant, if you see the trend of TSH levels increasing and you progressively feel the increasing number of symptoms. Talk to your doctor to determine what is the best therapy approach for you, and what is your, personal “normal” where you feel good.


  1. Carvalho GA et al. The clinical use of thyroid function tests (2013).
  2. Wartofsky L et al. The evidence for a narrower thyrotropin reference range is compelling (2005).
  3. Hollowell JG et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III) (2002).
  4. Dunn JT. Guarding our nation’s thyroid health (2002).
  5. Surks MI et al. Age-specific distribution of serum thyrotropin and antithyroid antibodies in the US population: implications for the prevalence of subclinical hypothyroidism (2007).
  6. Fontes R et al. Reference interval of thyroid-stimulating hormone and free thyroxine in a reference population over 60 years old and in very old subjects (over 80 years): comparison to young subjects (2013).
  7. Kumar A et al. Thyroid function tests in pregnancy (2013)
  8. Hubner U et al. Continuous age-dependent reference ranges for thyroid hormones in neonates, infants, children and adolescents established using the ADVIA Centaur Analyzer (2002).
  9. Lewandowsky K. Reference ranges for TSH and thyroid hormones (2015).
  10. Vadiveloo T et al. Age- and gender-specific TSH reference intervals in people with no obvious thyroid disease in Tayside, Scotland: the Thyroid Epidemiology, Audit, and Research Study (TEARS) (2013).
  11. http://apps.who.int/iris/bitstream/10665/66342/1/WHO_DIL_00.4_eng.pdf

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About the Author

Dr. Vedrana Högqvist Tabor is a CEO and co-founder of BOOST by VLM Health, aiming to prevent long-term health complications for people with autoimmune diseases. BOOST is a virtual assistant empowering patients through actionable personalized information, data recording, and data overview, as well as facilitating conversations with healthcare professionals. Vedrana and her team developed chatbot Hashiboto and the app BOOST is currently in the beta phase of testing. Open for people to test. Vedrana has a PhD in molecular biology. She has spent about 15 years as a researcher trying to find out the mechanism behind emerging and metastasis of cancer, as well as other complex diseases, and was multiple awarded for her research work. Vedrana’s goal is to prevent a late diagnosis of complex diseases through improving scientific tools we have, transforming our understanding of healthcare and usage of mobile and sensor technology. She believes that the right to information about how to maintain health should be one of our basic human rights. In her free time, Vedrana is a mentor at Stanford’s SPARK Berlin, writer on topics of health and technology, public speaker, and an amateur standup comedian. Vedrana lives in Berlin, Germany with her life partner and their dog.

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