Hashimoto’s disease, also known as chronic lymphocytic thyroiditis, is an autoimmune disorder that causes the immune system to attack and destroy the thyroid gland. This leads to hypothyroidism, or underactive thyroid, as the thyroid is no longer able to produce sufficient amounts of thyroid hormones. One of the key tests used to diagnose Hashimoto’s is the thyroid stimulating hormone (TSH) test.
What is TSH?
Thyroid stimulating hormone (TSH) is produced by the pituitary gland in the brain. When thyroid hormone levels in the body drop too low, the pituitary releases more TSH to stimulate the thyroid to produce more hormones. Therefore, TSH levels help determine how well the thyroid is functioning.
In a healthy individual, TSH levels usually range between 0.4 to 4.0 mIU/L. If the thyroid is underactive and not making enough hormones, the pituitary keeps releasing more TSH to try to spur the thyroid into action. This causes TSH levels to rise above the normal range.
TSH Range in Hashimoto’s
In Hashimoto’s disease, the immune attack on the thyroid causes it to gradually lose function over time. As a result, TSH levels start to increase as the pituitary tries harder and harder to stimulate an already damaged gland.
Some key TSH levels in Hashimoto’s include:
- 4.5-10 mIU/L: This mild TSH elevation indicates subclinical hypothyroidism and early thyroid failure. TSH is above range but not yet high enough to cause symptoms.
- Above 10 mIU/L: Overt hypothyroidism. The thyroid is severely underactive and unable to keep up with the body’s needs.
The higher the TSH, the more hypothyroidism has progressed. In some cases, TSH may rise well above 10 mIU/L into the 100s before a diagnosis is made.
TSH Threshold for Hashimoto’s Diagnosis
There is some debate around the TSH level that warrants a diagnosis of Hashimoto’s. Some doctors may not diagnose until TSH climbs above 10 mIU/L. However, many practitioners and medical guidelines support diagnosing Hashimoto’s at a TSH between 4-5 mIU/L along with positive thyroid antibodies.
Reasons for this lower threshold include:
- A TSH above 4 indicates the thyroid is starting to decline in function and antibodies are likely present.
- Diagnosing earlier allows quicker treatment to resolve symptoms and prevent long term complications.
- The normal TSH range may be too broad, with many people feeling best when TSH is below 2.5 mIU/L.
Treating Hashimoto’s aims to get TSH down to 1-2 mIU/L through medications like levothyroxine. This indicates the thyroid is getting adequate stimulation again.
TSH Trends and Hashimoto’s Progression
Tracking TSH over time can provide insight into how Hashimoto’s disease is progressing. In general:
- A gradually increasing TSH indicates the thyroid is being progressively damaged.
- A TSH that remains persistently elevated signals continued thyroid failure.
- Frequent changes or fluctuations in TSH can mean unstable thyroid function.
A declining TSH back down to the normal range shows the thyroid is responding well to treatment. However, TSH trends must be interpreted within the bigger clinical picture. Doctors also look at symptoms, thyroid hormone levels, thyroid antibodies, and treatment response.
TSH Alone Insufficient to Diagnose Hashimoto’s
An elevated TSH is just one piece of the puzzle in diagnosing Hashimoto’s thyroiditis. Looking at TSH alone can be misleading in some situations:
- Other causes of high TSH: TSH may temporarily rise during an illness, with certain medications, or in response to normal aging. Confirming Hashimoto’s requires thyroid antibodies.
- Normal TSH with thyroid antibodies: Some individuals have positive antibodies with a normal TSH if the thyroid is still compensating well. They are at high risk for developing hypothyroidism.
- Fluctuating TSH: In early Hashimoto’s, TSH may swing back and forth. Clinicians should review trends over several months vs. a single value.
Therefore, checking thyroid antibodies and free T4 is also essential. The combination of elevated TSH, low T4, and positive antibodies supports a definitive Hashimoto’s diagnosis.
Thyroid Antibodies in Hashimoto’s
Thyroid antibodies directly indicate that an autoimmune reaction is occurring against the thyroid. The two main antibodies are:
- Thyroid peroxidase antibodies (TPOAb): Present in 95% of people with Hashimoto’s. They are considered the classic Hashimoto’s antibody.
- Thyroglobulin antibodies (TgAb): Found in 60-80% of people with Hashimoto’s. May develop later or along with TPOAb.
Checking both antibodies provides the most accurate results. A positive test for one or both confirms Hashimoto’s as the cause of thyroid dysfunction.
Normal Antibody Ranges
Reference ranges for thyroid antibodies may vary slightly between labs. In general:
- Normal TPOAb: < 9 IU/mL
- Normal TgAb: < 4 IU/mL
Any result above the upper end of normal is considered positive or elevated.
Antibody Levels in Hashimoto’s
In Hashimoto’s, antibody levels are often significantly higher than the normal range. However, there is no specific threshold or antibody concentration that makes the diagnosis.
TPOAb levels above 20-30 IU/mL are typically seen. Extremely high levels exceeding 1,000 IU/mL are not uncommon. The higher the antibodies, the more vigorous the immune attack on the thyroid.
Some key notes about thyroid antibodies:
- Levels do not correlate with symptoms or determine the treatment approach.
- Antibodies can fluctuate or even become undetectable but Hashimoto’s remains.
- Falling antibody levels over time can indicate the immune attack is calming down.
Free T4 Level in Hashimoto’s
Free T4 measures the unbound and active thyroid hormone thyroxine in the bloodstream. This gives direct insight into the thyroid’s functional state. In Hashimoto’s, damaged thyroid tissue loses the ability to produce adequate T4.
The normal range for free T4 is generally 0.7-1.8 ng/dL. In Hashimoto’s, the T4 level typically drops below range or into the low end:
- Overt hypothyroidism: T4
- Subclinical hypothyroidism: T4 0.7-1.0 ng/dL
The lower the free T4, the more hypothyroidism has developed. Monitoring T4 helps determine if thyroid replacement medication needs to be adjusted.
However, some individuals maintain a normal free T4 as the thyroid is still compensating well despite antibody presence. Others have low T3 rather than T4. Evaluating multiple thyroid lab markers together gives the complete picture.
Reverse T3 in Hashimoto’s
Reverse T3 (RT3) is an inactivated form of T3 thyroid hormone that rises when the body is sick, stressed, or inflamed. Chronic illnesses like Hashimoto’s can drive up RT3 levels.
High RT3 in relation to low active T3 may contribute to ongoing hypothyroid symptoms in Hashimoto’s. However, RT3 testing is still considered controversial and not routinely ordered.
Research shows the ratio of RT3 to total T3 may be a helpful indicator. A ratio above 0.2 often correlates with fatigue and inflammation in autoimmune thyroid disease.
Diagnosing Hashimoto’s Without Elevated TSH
It is possible to have Hashimoto’s even with a normal TSH level. TSH can fluctuate, and some individuals maintain normal thyroid function for a long time before hypothyroidism develops.
Key patterns include:
- Isolated hypothyroxinemia: Normal TSH with low free T4 signaling declining function.
- Euthyroid sick syndrome: Normal labs but thyroid dysfunction symptoms due to autoimmunity.
- Central hypothyroidism: Pituitary dysfunction rather than thyroid causes low thyroid hormone levels.
Checking thyroid antibodies even with normal TSH can reveal Hashimoto’s in its early stages before overt hypothyroidism occurs.
Hashimoto’s Treatment if TSH Normal
Whether or not thyroid medication is warranted if TSH is normal depends on the clinical context:
- Symptomatic patients may benefit from a trial of low-dose thyroid hormone even if TSH is within range.
- If TPOAb or TgAb are very high, medication may help slow the autoimmune attack.
- L-thyroxine therapy is definitely indicated if T4 level is low or falling over time.
- Closely monitoring labs every 3-6 months is prudent to catch developing thyroid failure.
Treatment focuses on relieving symptoms, supporting the thyroid, and addressing underlying drivers like gut issues or nutrient deficiencies.
Other Lab Tests for Hashimoto’s
While TSH, T4, and antibodies are the primary lab markers used to diagnose Hashimoto’s, other tests can provide helpful supporting information:
Free T3
Checks unbound active T3 hormone levels, which tend to fall in hypothyroidism. Low T3 can persist even if T4 normalizes on medication.
Thyroid Ultrasound
Imaging to evaluate thyroid gland size, architecture, and nodules. Typifying Hashimoto’s findings include an enlarged, heterogeneous thyroid with diffuse inflammation.
Complete Blood Count
Anemia and low white blood cells may indicate impaired thyroid function. High platelet count can support autoimmunity.
Ferritin
Iron deficiency commonly co-occurs with hypothyroidism. Optimizing ferritin may help thyroid medication work better.
Vitamin D
Low vitamin D is highly prevalent in Hashimoto’s. Supplementing if deficient may help manage autoimmunity.
Celiac panel
Celiac disease and Hashimoto’s frequently overlap. Testing TTG IgA or total IgA and IgG can screen for celiac-related antibodies.
Adrenal panel
Cortisol, DHEA-S, and other adrenal hormones may identify co-existing adrenal dysfunction or insufficiency.
The Takeaway
An elevated TSH over 4.5-10 mIU/L, particularly in combination with high thyroid antibodies and low thyroid hormones, strongly indicates Hashimoto’s thyroiditis. However, TSH is just one piece of the diagnostic process.
Changes in TSH mirror the thyroid’s declining functional state. But confirming Hashimoto’s requires assessing T4 levels plus thyroid antibodies like TPOAb and TgAb.
Individuals can have Hashimoto’s even with a normal TSH early on or if the pituitary is dysfunctional. Evaluating the whole clinical presentation and trends over time is necessary for an accurate diagnosis.
Close monitoring of thyroid labs is important for identifying Hashimoto’s thyroiditis, determining treatment needs, and tracking disease progression over the long term.