Skip to Content

What levels indicate Hashimoto’s?

Hashimoto’s thyroiditis, also known as chronic lymphocytic thyroiditis, is an autoimmune disorder that causes the immune system to attack and destroy the thyroid gland. This results in hypothyroidism, or an underactive thyroid. There are several lab tests that can help diagnose Hashimoto’s by looking at levels of different thyroid hormones and antibodies.

TSH

One of the most common first tests ordered when a doctor suspects hypothyroidism or Hashimoto’s is TSH, or thyroid stimulating hormone. TSH is produced by the pituitary gland in the brain, which regulates the production of thyroid hormones. Here are the normal reference ranges for TSH:

  • General adult range: 0.4 – 4.0 mIU/L
  • Newborn range: 0.7 – 15.2 mIU/L
  • 1-6 months: 0.6 – 6.0 mIU/L
  • 6-12 months: 0.7 – 5.7 mIU/L
  • 1-5 years: 0.7 – 5.7 mIU/L
  • 6-12 years: 0.7 – 5.5 mIU/L
  • 13-19 years: 0.7 – 5.3 mIU/L

In Hashimoto’s, the TSH level is often elevated beyond the normal range, indicating the pituitary gland is trying to stimulate more thyroid hormone production. A TSH above the reference range, along with symptoms of hypothyroidism, is an indicator of Hashimoto’s.

Free T4

Free T4 measures the level of unbound thyroxine hormone available in the bloodstream. This gives an indication of how much active thyroid hormone is present to carry out the thyroid’s functions in the body. Normal reference ranges for free T4 are:

  • 0.8 – 1.8 ng/dL for adults
  • 0.7 – 2.0 ng/dL for children

In Hashimoto’s, the free T4 is often low because thyroid hormone production is decreasing. A low or low-normal free T4 along with an elevated TSH points to hypothyroidism caused by Hashimoto’s.

Free T3

Free T3 measures unbound triiodothyronine, which is another thyroid hormone. Normal ranges are:

  • Adults: 2.3 – 4.2 pg/mL
  • Children:
    • 1-3 days old: 3.1 – 6.9 pg/mL
    • 4-10 days old: 3.5 – 6.5 pg/mL
    • 2-20 weeks old: 2.8 – 6.4 pg/mL
    • 21 weeks – 19 years old: 2.5 – 5.8 pg/mL

In Hashimoto’s, the free T3 may be low or within the lower end of the normal range. Measuring free T3 helps determine if conversion of T4 to T3 is impaired in someone with low thyroid levels.

Thyroid Peroxidase Antibodies

Thyroid peroxidase (TPO) antibodies are autoantibodies that attack thyroid peroxidase, an enzyme needed for thyroid hormone production. A high level of TPO antibodies indicates Hashimoto’s thyroiditis. Normal ranges are:

  • Normal: Under 9 IU/mL
  • Borderline: 9-35 IU/mL
  • High: Over 35 IU/mL

TPO antibodies are present in 95% of people with Hashimoto’s. Levels may correlate with disease activity – people with very high levels (>1000 IU/mL) tend to have more inflamed thyroid tissue.

Thyroglobulin Antibodies

Thyroglobulin (Tg) antibodies attack thyroglobulin, a protein used in thyroid hormone production. Tg antibodies can also help diagnose Hashimoto’s. Normal ranges are:

  • Normal: Under 4 IU/mL
  • High: Over 4 IU/mL

About 60-80% of people with Hashimoto’s test positive for elevated Tg antibodies. A high level indicates an autoimmune disorder and ongoing immune system destruction of thyroid tissue.

Other Tests

There are a few other lab tests that may be ordered to evaluate thyroid function:

  • Total T4: measures both bound and unbound T4. Total T4 levels tend to be normal in the early stages of Hashimoto’s but may decrease as the disease progresses.
  • Total T3: measures both bound and unbound T3. Total T3 may be low or low-normal.
  • Reverse T3: inactive form of T3 that is high in some thyroid disorders. Not routinely tested in Hashimoto’s.
  • Thyroid ultrasound: can check thyroid size and look for inflammation or nodules. Many people with Hashimoto’s have an enlarged thyroid gland early on.
  • Radioactive iodine uptake (RAIU): measures how much iodine the thyroid takes up from the bloodstream. May be used to evaluate the cause of thyroid problems.

Key Takeaways

Here are some of the main lab abnormalities that can indicate Hashimoto’s thyroiditis:

  • Elevated TSH and low/low-normal free T4 – indicates hypothyroidism
  • Positive TPO antibodies – present in 95% of Hashimoto’s patients
  • Positive Tg antibodies – present in 60-80% of Hashimoto’s patients
  • Low/low-normal free T3 – indicates impaired T4 to T3 conversion
  • Enlarged thyroid on ultrasound – suggests thyroid inflammation

The combination of elevated TSH and positive thyroid antibodies is enough for a diagnosis of Hashimoto’s in most cases. The other thyroid hormone levels help confirm that autoimmune destruction of the thyroid is causing hypothyroidism.

While reference ranges provide a guide, the optimal TSH for an individual may fall outside the standardized range. Doctors also look at clinical symptoms and thyroid antibody presence when diagnosing Hashimoto’s.

Typical Pattern of Lab Changes

Hashimoto’s thyroiditis develops slowly over months to years. The typical pattern of lab changes is:

  1. Normal thyroid function tests but positive TPO and/or Tg antibodies
  2. Slightly elevated TSH, remainder of thyroid panel still normal
  3. Overt hypothyroidism – high TSH, low free T4, low or low-normal free T3

As Hashimoto’s progresses, TSH gradually increases while free thyroid hormone levels decrease. Mild TSH elevation may resolve back to normal briefly, but eventually worsens over time.

Hashimoto’s with Normal Thyroid Levels

Some individuals have positive thyroid antibodies and symptoms of hypothyroidism, but normal TSH, free T4 and T3 levels. This is sometimes referred to as Hashimoto’s encephalopathy or euthyroid Hashimoto’s. Treating these patients with thyroid hormone replacement can improve symptoms.

Monitoring TSH and Antibodies

Once diagnosed, periodic monitoring of TSH and thyroid antibodies helps assess whether thyroid function is stable or gradually worsening. Guidelines recommend:

  • Check TSH and antibodies every 6-12 months once stable on thyroid medication
  • Monitor TSH more frequently when adjusting thyroid medication doses
  • Yearly TSH screening for family members with a history of Hashimoto’s or autoimmune thyroid disease

Some doctors also monitor clinical symptoms and use age-adjusted TSH ranges to guide treatment decisions.

Hashimoto’s Treatment

Treatment for Hashimoto’s focuses on replacing thyroid hormone to treat hypothyroidism. Levothyroxine, a synthetic thyroxine, is typically the medication of choice. Finding an optimal dose that resolves symptoms may take months.

A gluten free diet may improve symptoms and thyroid antibodies in Hashimoto’s patients with gluten sensitivity. Selenium supplements may help lower thyroid antibody levels. Treating other autoimmune conditions and reducing stress can help improve well-being.

FAQs

How high can TSH go with Hashimoto’s?

In untreated Hashimoto’s, TSH levels may rise well above the reference range, sometimes over 100 mIU/L. The highest TSH levels are typically seen in more advanced Hashimoto’s thyroiditis.

What is a dangerous TSH level?

There is no specific TSH level considered dangerous. However, extremely high TSH levels over 100 mIU/L can sometimes cause issues like an enlarged thyroid gland (goiter), slowed thinking and movement, and impaired heart function.

Can TSH be high and T4 normal?

Yes, in the early stages of Hashimoto’s thyroiditis TSH may become slightly elevated while free T4 and T3 remain in the normal range. Over time, free T4 usually decreases as hypothyroidism progresses.

Can Hashimoto’s make your TSH low?

No, Hashimoto’s will not directly lower TSH levels. However, some Hashimoto’s patients develop temporary hyperthyroidism (overactive thyroid) when the inflamed thyroid releases excess thyroid hormone. This short-term hyperthyroid phase can briefly suppress TSH.

The Bottom Line

Hashimoto’s thyroiditis is diagnosed when a patient has high thyroid antibodies (TPOAb and/or TgAb) and hypothyroid symptoms or TSH elevation. Checking TSH, free T4, free T3 and thyroid antibodies identifies the characteristic pattern of hormonal changes in Hashimoto’s.

Following antibody levels and thyroid function tests over time allows for proper monitoring of Hashimoto’s thyroiditis progression and guiding of treatment decisions.