TSH results explained: what TSH, free T4 and free T3 on your lab report mean, and how to prepare for the visit

Your lab report lists TSH, free T4 and maybe free T3, each next to a printed range. You can keep those reports in a folder or in Sam's Health Vault: your own copy, separate from the records your practice keeps. This guide explains what the numbers mean, why symptoms and TSH don't always match, and what to bring to your doctor.

What do TSH, free T4 and free T3 mean?

TSH stands for thyroid-stimulating hormone. It comes from the pituitary gland at the base of the brain. It tells the thyroid to produce its hormone. When the thyroid makes too little, TSH goes up. So a high TSH can be a sign of an underactive thyroid.

Free T4 is the part of the hormone thyroxine that circulates freely. It is the share your body can actually use, and it shows whether thyroid hormone is really low.

Free T3 is the other free thyroid hormone. The British Thyroid Foundation says it is mainly used when testing for an overactive thyroid. The American Thyroid Association says a T3 test is not often needed for an underactive one.

Read together, TSH and free T4 form a pattern.

If TSH is raised, your doctor may also test for TPO antibodies. They can show whether the immune system is damaging the thyroid, as in Hashimoto's thyroiditis. The difference is explained in Hypothyroidism vs Hashimoto's. Which tests you get is your doctor's call. Who orders them and how the diagnosis works step by step is in How is hypothyroidism diagnosed?.

What does the range next to each number mean?

The range comes from the lab that ran your test. The British Thyroid Foundation notes that ranges are only a guide and vary between laboratories. So read each value against the range on the same report.

Age matters for TSH, because it rises naturally over the years. The 2023 German family medicine guideline (DEGAM) therefore uses upper limits by age.

• 18 to 70 years: above 4.0 mU/L counts as raised.
• 70 to 80 years: above 5.0 mU/L.
• Over 80 years: above 6.0 mU/L.

Labs still often print one range for all ages. Sam, too, compares a value only with the range printed on your report, not with these age limits. Your doctor reads your results together with your age, free T4, symptoms and medicines.

A worked example with invented numbers: a report shows TSH at 6.8 mU/L, with a range of 0.4 to 4.0. Free T4 is 15 pmol/L, with a range of 10 to 23. So TSH sits above its range and free T4 inside it. That is the pattern of subclinical hypothyroidism. For a first raised TSH up to 10 mU/L and an unremarkable history, the DEGAM guideline repeats the test first. Above 10 mU/L, or with a notable history, it adds further tests. What this means for you is a conversation with your doctor. The example does not classify your own result. If you have symptoms, they get worse, or you are pregnant or planning a pregnancy, do not wait for a repeat test: contact your doctor now.

Why don't my symptoms match my TSH?

A raised TSH often causes no symptoms at all. The German family medicine guideline (DEGAM) says a raised TSH mostly turns up by chance, in a blood test done for other reasons.

The reverse also happens. Tiredness, poor concentration and dry skin are common symptoms of an underactive thyroid, according to the NHS. But many of these symptoms can have other causes, as informedhealth.org and the American Thyroid Association point out. Your symptoms still count. The British Thyroid Foundation says your doctor reads the tests together with your symptoms and how you feel.

TSH also moves around. According to IQWiG, it is highest at night and lowest in the afternoon. The German Society of Endocrinology adds acute sleep loss, physical exertion, infections and biotin as influences. It says single measurements need great caution.

Symptoms can also continue once you take thyroid hormone. The European Thyroid Association's 2012 guideline describes people who still have symptoms with a normal TSH. The cause is not always clear. The guideline assumes other causes, such as anemia, were ruled out first.

How you feel is part of the decision. Under the DEGAM guideline, adjustments follow both the thyroid results and how you feel. So raise symptoms like these with your doctor. Do not change your intake on your own.

A few weeks of notes give you something concrete to talk from. In Sam's symptom diary, you log fatigue, hair loss, dry skin, constipation or low mood once a day. Each is rated mild, moderate or severe. Confusion or brain fog is logged as present. Feeling cold is not in the catalog, so you add it under "Other". For what a useful diary holds, see symptom diary: paper template or app.

How often is TSH checked?

Your doctor sets the schedule. The sources describe a similar pattern.

• At the start, blood tests usually come every few weeks, says the British Thyroid Foundation. The American Thyroid Association names a check 6 to 8 weeks after starting or changing the dose.
• Once things are stable, a TSH test once a year is usual, according to the British Thyroid Foundation and informedhealth.org.
• A raised TSH may turn up without symptoms. The German Society of Endocrinology then advises a second test before thyroid hormone is started. It should come at least 2, ideally 6 months after the first.
• Subclinical hypothyroidism may be left untreated. The DEGAM guideline then allows a recheck after six to twelve months. This is to rule out passing causes such as an acute illness.

TSH changes over the day. So ask your practice whether to come at the same time each time. Ask too whether to fast and when to take your medication on test day.

If symptoms start or get worse, or you are pregnant or planning a pregnancy, do not wait for the next planned check. Contact your doctor sooner. The NHS advises people with an underactive thyroid to tell their GP when they are pregnant or planning to be, and the DEGAM guideline sets its own upper TSH limit for pregnancy.

What should you bring to the appointment?

• Your earlier lab reports with dates, not just the latest number. If you need copies, see getting a copy of your medical records.
• A list of every medicine, including over-the-counter products and supplements. The British Thyroid Foundation asks you to mention anything that might affect the readings. It names supplements with iodine or biotin in particular. The medication list guide covers what else belongs on it.
• A few notes on your symptoms: which ones, since when, on how many days, how strong.
• Your questions. Which range applies to my age? When is my next check? Should I fast, and when do I take my medication on test day? Were free T4 or TPO antibodies tested?

In Sam, your lab reports, symptom diary and medication list sit in the same app. In Sam Chat you can ask questions about your own reports; the answers are based on your data and are not medical advice. You create the monthly report yourself, from the 1st for the previous month. It needs notifications, access to your health data, an entry on chronic conditions ("none" counts) and, from the second report on, your daily status logged on at least 15 of the last 30 days. The PDF shows your symptom days and five most frequent symptoms and counts the lab reports you added. Lab values and your medication list are not in it, so show those in the app. What you keep in Sam with an underactive thyroid is in the hypothyroidism overview.

When should you not wait for your appointment?

In very rare cases, a severe underactive thyroid can lead to a life-threatening condition called myxoedema coma. The NHS describes it as an emergency that needs hospital care.

Some signs mean a life-threatening emergency: severe trouble breathing, chest pain, sudden confusion, being very hard to wake, or passing out. Call your local emergency number right away (112 in the EU, 999 in the UK, 911 in the US). With a known underactive thyroid, very strong drowsiness, confusion or an unusually low body temperature count too. Do not wait for it to pass. For anything urgent but not life-threatening when your practice is closed, use the out-of-hours service where you live.

Low mood is one of the listed symptoms of an underactive thyroid. If you have thoughts of harming yourself, call your local emergency number or a crisis line right away. In the UK and Ireland, Samaritans answer free, day or night, on 116 123. In the US, you can call or text 988, the Suicide & Crisis Lifeline, at any hour.

Keep lab reports, symptoms and doses together in Sam

You bring reports, symptoms and doses to the visit in one app.

• Instead of a folder: with your consent, Sam reads your lab reports for TSH, free T4 and free T3. Check values against the original. If your last two reports use the same unit, you see up to three of the biggest changes.
• Instead of memory: you log fatigue, hair loss or low mood day by day. You create the monthly report yourself; it shows symptom days and your five most frequent symptoms.
• Instead of a paper note: the medication list reminds you at set times, and you tick off each dose. A catalog pick may preset a strength: check your pack. Your doctor sets the dose.

Sam only shows whether a value is above or below your lab's printed range. More in the hypothyroidism overview.

Try Sam for free

Sam is a wellness companion, not a medical device. The app does not diagnose, treat, cure or prevent any disease or health condition. Always consult qualified professionals for medical decisions.

Related reading

• Medication list for your doctor: what to include
• Symptom diary: paper template or app?
• Getting a copy of your medical records when changing doctor
• Hypothyroidism vs Hashimoto's: What Is the Difference?
• How Is Hypothyroidism Diagnosed? Doctor and Blood Tests

Sources

Updated: October 2026

• NHS: Underactive thyroid (hypothyroidism) (last reviewed 28 April 2025)
• British Thyroid Foundation: Thyroid function tests (updated 8 October 2026)
• American Thyroid Association: Hypothyroidism
• IQWiG (informedhealth.org): Underactive thyroid (hypothyroidism) (updated 28 May 2024)
• IQWiG (gesundheitsinformation.de): Thyreoidea-stimulierendes Hormon (TSH) (updated 20 March 2025, in German)
• European Thyroid Association: 2012 ETA guideline on hormone replacement in hypothyroidism, Wiersinga WM et al., Eur Thyroid J 2012;1(2):55-71
• DEGAM S2k guideline "Erhöhter TSH-Wert in der Hausarztpraxis" (AWMF 053-046, 2023), summarised by Diederich S, Freitag M in Arzneiverordnung in der Praxis 2024;51(2) (PDF) (in German)
• DEGAM: S2k guideline Erhöhter TSH-Wert in der Hausarztpraxis, long version (PDF) (AWMF 053-046, April 2023, in German; revision planned for May 2027)
• German Society of Endocrinology (DGE): Schilddrüse: Wenn der TSH-Wert erhöht ist (press release, 29 August 2023, in German)
• MedlinePlus: Recognizing medical emergencies (reviewed 8 January 2025)
• Acharya R et al.: Myxedema Coma: A Forgotten Medical Emergency With a Precipitous Onset, Cureus 2020;12(9):e10478
• Samaritans: Contact a Samaritan
• 988 Suicide & Crisis Lifeline: 988lifeline.org