What Does a High TPO Level Mean With Hashimoto's?

You get your blood test results back and suddenly see TPO antibodies listed. Maybe the number is much higher than you expected.

But what does it actually mean?

Does a high TPO level mean your Hashimoto's is getting worse? Can the number tell you how severe your Hashimoto's is? And should you be trying to lower it?

Those are completely understandable questions.

What Are TPO Antibodies?

TPO stands for thyroid peroxidase, an enzyme your thyroid needs to produce thyroid hormones.

With Hashimoto's, the immune system produces antibodies that target components of the thyroid. One of these is TPO antibodies (anti-TPO).

An elevated anti-TPO level can therefore be an important indication of Hashimoto's.

You can think of it as evidence that the immune system is involved in what is happening in your thyroid.

How High Is a High TPO Level?

There isn't one universal cutoff that applies to every laboratory.

Different laboratories may use different testing methods and reference ranges. That's why you should always compare your result with the reference range shown on your own laboratory report.

A result considered elevated by one laboratory may have a different reference range at another.

Does a Higher TPO Level Mean More Symptoms?

Not necessarily.

This is probably the most important thing to understand.

The level of your anti-TPO antibodies does not directly tell you how severe your symptoms will be.

You can have a high TPO level and feel relatively well. Someone else may have a lower level and experience significant symptoms.

TPO antibodies are mainly useful as an indication of the autoimmune component of Hashimoto's. To assess how well your thyroid is functioning, TSH and FT4 are particularly important.

Can a High TPO Level Cause Your Symptoms?

It's tempting to look at one blood result and think:

“That's what's causing everything.”

But Hashimoto's usually isn't that simple.

Symptoms such as fatigue, feeling cold, hair loss, dry skin, weight gain or brain fog can occur with hypothyroidism, but they don't tell you on their own how much autoimmune activity is present.

That's why healthcare professionals look at several pieces of information:

How is your thyroid functioning?
What symptoms are you experiencing?
What are your TSH and FT4 levels?
Are TPO antibodies present?
What does your individual situation look like?

The whole picture matters more than one number.

Do You Need to Keep Checking Your TPO Level?

Not necessarily.

Once Hashimoto's has been diagnosed, treatment for hypothyroidism is generally not adjusted based on the anti-TPO level alone.

TSH and FT4 are much more important when assessing thyroid function and treatment. Repeated TPO testing generally doesn't provide information that changes treatment.

So you don't necessarily need to worry every time your TPO level remains elevated.

Can a High TPO Level Become Normal?

Anti-TPO antibody levels can change over time. In some people they decrease, while in others they remain elevated.

But a lower TPO level doesn't automatically mean that Hashimoto's has disappeared.

And a high TPO level doesn't automatically mean that your thyroid is functioning worse at that particular moment.

That's why it usually isn't helpful to focus entirely on trying to “get your TPO down.”

What If Your TSH and FT4 Are Normal?

This can be confusing.

You can have positive TPO antibodies while your TSH and FT4 are still within the normal range.

This means there is evidence of an autoimmune response involving the thyroid, but your thyroid may still be producing enough hormone at that point.

That's one reason Hashimoto's can be present before someone develops clear hypothyroidism.

You can therefore have Hashimoto's without currently having an underactive thyroid.

What If Your TPO Is Very High?

Seeing a very high TPO level on your blood test can be frightening, especially when you see the number for the first time.

But try not to think of it as a “severity score” for Hashimoto's.

A TPO level of 500 doesn't automatically mean someone has five times as many symptoms as someone with a level of 100.

The result needs to be interpreted alongside your other thyroid results and your symptoms.

The Most Important Thing to Remember

A high TPO level mainly tells you something about the autoimmune response associated with Hashimoto's.

It does not tell you exactly:

how many symptoms you'll have;
how severe your Hashimoto's is;
how well your thyroid is currently functioning;
whether your medication needs to be changed.

Other information, particularly thyroid function, is needed for that.

So if you see a high TPO level on your blood test, it doesn't automatically mean that something is urgently wrong.

It's one piece of the puzzle.

And perhaps that's the most useful way to think about thyroid blood tests with Hashimoto's: not as individual numbers that determine how you “should” feel, but as information that becomes meaningful when considered alongside your symptoms and other results.