Hypothyroidism vs Hashimoto's: a cause, a state, and the blood tests that tell them apart

Your doctor's letter says "Hashimoto's thyroiditis", but in the appointment everyone talked about an underactive thyroid. Are these two conditions or one? Lab reports, letters and an ultrasound report can go into a folder or into Sam's Health Vault: your own copy, separate from the records your practice keeps. This guide explains how the two terms differ, which blood tests belong to which, and what else causes an underactive thyroid.

The short version: Hashimoto's is a cause, and hypothyroidism is a state. They often go together, but they are not the same thing. For what TSH, free T4 and free T3 each mean, read TSH results explained. For what you can keep in Sam, see the hypothyroidism overview.

Is Hashimoto's the same as hypothyroidism?

No. Hypothyroidism means the thyroid makes too little hormone. It describes how the gland works, not why.

Hashimoto's thyroiditis is one reason why. The immune system turns against the thyroid and keeps it inflamed. That makes it an autoimmune condition. The NHS calls it the main cause of an underactive thyroid in the UK. Informedhealth.org says the same for Germany, where about 5 in 100 people have an underactive thyroid.

So the two terms overlap without matching. The inflammation can be there while thyroid levels are still normal. And hypothyroidism can have quite different causes.

The table sorts out terms. It is not a test to run on yourself: which one applies to you is for your doctor to say.

Which blood tests point to which?

The tests answer two different questions. The American Thyroid Association (ATA) puts it plainly: TSH and free T4 tell you how the thyroid is actually working. Antibodies help pin down the cause.

• TSH goes up when the thyroid makes too little hormone.
• Free T4 shows whether thyroid hormone is actually low. With high TSH and a normal free T4, doctors speak of subclinical hypothyroidism.
• TPO antibodies target an enzyme in the thyroid (thyroid peroxidase). The German family medicine guideline (DEGAM) says they are raised in about 90 in 100 people with Hashimoto's.
• Thyroglobulin antibodies (Tg antibodies) are raised in about 70 in 100, per the same guideline.

Antibodies alone do not make it Hashimoto's. TPO antibodies show up in 7 to 14 in 100 people in the general population, says DEGAM. They are also common in other autoimmune conditions. The British Thyroid Foundation (BTF) adds that positive antibodies occur in people without thyroid disease. Under DEGAM, positive TPO antibodies with no overt hypothyroidism on the lab report and no matching ultrasound are not enough for the diagnosis.

When are they tested? DEGAM, in its 2023 guideline for family doctors, says:

• With subclinical hypothyroidism, TPO antibodies may be tested once to check for Hashimoto's.
• If they are negative, a minority vote of the German Society of Endocrinology allows one Tg antibody test. Some people with autoimmune thyroiditis only have Tg antibodies.
• With TSH in the normal range, TPO antibodies should not be tested.
• They should not be repeated, because the course of antibody levels has no consequence for care. The BTF and the ATA say the same: repeat antibody tests rarely help.
• With overt hypothyroidism, the antibody result does not change the family doctor's next steps. It can still help people who want to understand their cause, though the guideline notes it can also unsettle some.

Which tests you get is up to your doctor.

Can you have Hashimoto's without hypothyroidism?

Yes. The ATA describes people whose antibody levels are high while their thyroid levels are normal. Early on you may have no symptoms at all, even with antibodies in the blood. If you are not yet treated and have high antibodies with normal TSH and free T4, the ATA says you do not need treatment. If your underactive thyroid is already treated, do not change your intake on your own.

Hypothyroidism can develop later. With subclinical hypothyroidism and positive TPO antibodies, the risk is slightly higher, according to DEGAM. The level of TSH matters more. Informedhealth.org reports that 2 to 5 in 100 people with subclinical hypothyroidism develop hypothyroidism with symptoms each year.

What happens with subclinical hypothyroidism plus Hashimoto's is a careful joint decision with your doctor, says DEGAM. Your doctor also sets how often to recheck. If symptoms get worse, new ones appear, or you are pregnant or planning a pregnancy, do not wait for the next planned check. Contact your doctor sooner. The DEGAM guideline sets its own upper TSH limit for pregnancy.

Can you have Hashimoto's without raised TPO antibodies?

It happens. DEGAM says TPO antibodies are raised in about 90 in 100 people with Hashimoto's, and not in the rest. So a TPO result that is not raised does not rule Hashimoto's out for certain. And as above, some people only have Tg antibodies.

An ultrasound can give clues too. A hypoechoic thyroid picks up autoimmune inflammation even more sensitively than TPO antibodies, according to DEGAM. The ATA notes that ultrasound can show inflammation early, while levels are still normal. But for a raised TSH, the finding does not change the decision about care, says DEGAM. It advises against routine ultrasound when TSH is raised. The ATA also says an ultrasound may or may not be needed.

Whether you need one, and whether you have Hashimoto's, is for your doctor to judge.

What else causes hypothyroidism?

The NHS, the ATA, informedhealth.org and DEGAM list, among others:

• surgery that removed part or all of the thyroid
• radioactive iodine or radiation around the neck
• treatment for an overactive thyroid
• certain medicines
• other forms of thyroiditis
• severe iodine deficiency, which the NHS calls rare in the UK
• a thyroid that did not work properly from birth, which is rare
• rarely, a problem with the pituitary gland or hypothalamus

With that last group, TSH is not raised but low, says DEGAM. The ATA says a low TSH with a low free T4 points to the pituitary.

Not every underactive thyroid stays. With some other forms of thyroiditis, most people's thyroid function returns to normal within 12 to 18 months, according to the ATA. With Hashimoto's, hypothyroidism is usually permanent. A raised TSH can also be temporary, for example after an acute illness or because of medicines (DEGAM). Depending on the cause, care may be temporary or lifelong, says informedhealth.org.

Because medicines can be a cause, bring a full list to your appointment, including over-the-counter products and supplements. The medication list guide covers what belongs on it.

Do Hashimoto's symptoms differ from other hypothyroidism?

Hardly. When thyroid hormone is lacking, metabolism slows down, says informedhealth.org. That is where the symptoms come from, whatever the cause. The ATA therefore lists the same symptoms for Hashimoto's as for hypothyroidism. They include tiredness, feeling cold, constipation, dry skin and depression. The NHS adds trouble concentrating, hair loss, a hoarse voice and irregular or heavy periods.

The sources describe two things specific to Hashimoto's:

• The inflammation can enlarge the thyroid, called a goiter (ATA). That is one reason a GP may examine your neck, says the NHS.
• Rarely, Hashimoto's comes with a short-lived overactive phase. The ATA calls such cases rare.

While levels are still in range, you may have no symptoms at all, says the ATA. And the usual symptoms have many other possible causes. Why symptoms and TSH don't always match is covered in TSH results explained.

What should you keep from the work-up?

Finding the cause leaves a trail of paper. There are lab reports with TSH, free T4 and maybe antibodies. There is a doctor's letter naming the cause, and sometimes an ultrasound report. Keep them with their dates, older ones included. If you need copies, see getting a copy of your medical records.

In Sam, they go into the Health Vault. With your consent, Sam reads about 33 lab values by name from your reports, including TSH, free T4 and free T3. TPO and Tg antibodies are not among those named values. If such a row is printed, Sam usually takes it over under its printed name. Some rows land under the wrong name: a TSH receptor antibody row can be saved as TSH, for example. So check every value Sam reads against your original report.

If the report prints a range, you see the value beside it. If one lab prints a different unit from the other, Sam does not compare that line. Between your last two lab reports, Sam shows up to three of the biggest changes. An antibody value printed on both reports can show up there too. Under DEGAM, though, the course of antibody levels has no consequence for care.

Your doctor's letter and ultrasound report go in as documents of their own. With your consent, Sam writes a short summary, and you confirm it. Whether Hashimoto's is your cause is in your doctor's letter.

When do you need help right away, whatever the cause?

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 on 116 123, day or night. In the US, you can call or text 988, the Suicide & Crisis Lifeline, at any hour.

Keep your Hashimoto's and thyroid reports in Sam

Your lab reports, doctor's letter and ultrasound report sit in one app at your visit.

• Instead of a folder: you scan or import each report and keep your own copy, separate from your practice's records.
• Instead of retyping: with your consent, Sam reads your lab reports for TSH, free T4 and free T3. Antibody rows usually keep their printed name. Check each value against the original.
• Instead of leafing through: if both print the same unit, you see up to three of the biggest changes between your last two reports.
• Instead of a paper pile: with your consent, Sam summarises a doctor's letter or ultrasound report, and you confirm it.

Whether Hashimoto's is the cause is for your doctor to say. 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

• How Is Hypothyroidism Diagnosed? Doctor and Blood Tests
• TSH results explained: hypothyroidism and your doctor visit
• Medication list for your doctor: what to include
• Getting a copy of your medical records when changing doctor
• Symptom diary: paper template or app?

Sources

Updated: October 2026

• NHS: Underactive thyroid (hypothyroidism) (last reviewed 28 April 2025)
• American Thyroid Association: Hashimoto's Thyroiditis
• American Thyroid Association: Thyroiditis
• American Thyroid Association: Thyroid Function Tests
• British Thyroid Foundation: Thyroid function tests (updated 8 October 2026)
• IQWiG (informedhealth.org): Underactive thyroid (hypothyroidism) (updated 28 May 2024)
• DEGAM: S2k guideline Erhöhter TSH-Wert in der Hausarztpraxis, long version (PDF) (AWMF 053-046, April 2023, in German; sections 4, 5.4.3 on thyroid autoantibodies, 5.4.4 on ultrasound, and 6; revision planned for May 2027)
• 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