Thyroid stimulating hormone (TSH) is an important hormone that is released by the pituitary gland in the brain. It plays a key role in regulating thyroid hormone levels in the body. TSH influences how much thyroid hormone is produced and released by the thyroid gland. In most cases, a TSH level within the normal range indicates that the thyroid is functioning properly. However, in some situations, a high TSH level may still be considered normal.
What is TSH?
TSH is a hormone that is released by the pituitary gland, a small gland located at the base of the brain. When TSH levels in the blood are low, this signals to the thyroid gland to produce more thyroid hormone. The main thyroid hormones are T3 (triiodothyronine) and T4 (thyroxine). When TSH levels are high, this tells the thyroid gland that enough thyroid hormone is being produced, and it should slow down hormone production.
This feedback loop allows TSH to maintain thyroid hormone levels within a normal range. TSH production is controlled by TRH (thyrotropin-releasing hormone), which is made by the hypothalamus. The hypothalamus monitors thyroid hormone levels and releases TRH when more TSH is needed to stimulate thyroid hormone production.
Functions of TSH
- Stimulates the thyroid gland to produce thyroid hormones T3 and T4
- Regulates growth and function of the thyroid gland
- Part of the feedback loop that maintains optimal thyroid hormone levels
Normal TSH Reference Range
There is no single TSH level that is considered definitively normal. TSH reference ranges tend to fall between 0.5 and 5.0 mIU/L, though the exact normal values can vary by factors like age and stage of life:
| Age Group | Normal TSH Range (mIU/L) |
|---|---|
| Newborns (0-1 month) | 0.5 – 15 |
| Infants (1-12 months) | 0.8 – 8 |
| Children (1-10 years) | 0.5 – 5.5 |
| Adolescents (10-19 years) | 0.5 – 4.5 |
| Adults (20-50 years) | 0.4 – 4.0 |
| Pregnant women | 0.1 – 2.5 |
As a general guideline, a TSH level above the normal range may indicate an underactive thyroid gland, while a TSH below the normal range can signal an overactive thyroid. However, as we’ll discuss next, there are some situations where a TSH outside of the reference range may still be considered normal for an individual.
When Can a High TSH Be Normal?
In most healthy individuals, a high TSH level is an indication that thyroid hormone levels are too low. This typically reflects an underactive thyroid gland. However, there are some circumstances when a high TSH may still fall within an acceptable range:
1. At the Upper End of the Normal Range
If your TSH is slightly above the normal range but falls within what is considered the upper end of normal, it may not necessarily indicate a problem. For example, if the normal range is considered 0.5-5.0 mIU/L, a TSH of 4.5 or 5.0 may still be within normal limits, especially if there are no symptoms of hypothyroidism present.
2. During Pregnancy
The TSH range is lower during pregnancy, typically between 0.1-2.5 mIU/L. TSH levels can fluctuate during pregnancy due to the effects of human chorionic gonadotropin (hCG). As a result, TSH levels that would be considered high outside of pregnancy may still be normal in a pregnant woman.
3. In Older Adults
As we age, the normal TSH range tends to shift upward. TSH levels above 5.0 mIU/L may be considered normal and not indicate hypothyroidism in adults over the age of 60, especially when thyroid hormone levels are normal.
4. Due to Individual Variation
There is natural variation in what is considered a “normal” TSH level between individuals. Some people simply have a higher TSH baseline. If your TSH is above the reference range but thyroid hormone levels are normal, you may represent healthy variation rather than have an underlying problem.
5. Subclinical Hypothyroidism
In subclinical hypothyroidism, the TSH level is elevated but circulating thyroid hormone levels remain within the normal range. This represents very mild thyroid failure that may not necessarily require treatment right away. Whether high TSH in subclinical hypothyroidism should be treated or not depends on other factors like symptoms and risk factors.
What Causes High TSH?
Some common causes of an elevated TSH include:
- Hypothyroidism: An underactive thyroid is the most common reason for persistently high TSH. This includes Hashimoto’s disease, where the immune system attacks the thyroid.
- Pituitary disorders: Tumors or other diseases affecting the pituitary gland can impair TSH production and elevate levels.
- Medications: Some drugs like lithium and certain painkillers can impact thyroid function and raise TSH.
- Pregnancy and postpartum: Hormone fluctuations during and after pregnancy can lead to high TSH.
- Aging: TSH levels may increase slightly as we get older.
- Non-thyroidal illness: Serious acute or chronic illness can temporarily increase TSH.
- Iodine deficiency: Lack of sufficient dietary iodine causes hypothyroidism and elevated TSH.
Signs and Symptoms of High TSH
Some signs and symptoms that may be present with an elevated TSH include:
- Fatigue
- Weight gain or difficulty losing weight
- Feeling cold
- Dry skin
- Constipation
- Muscle weakness
- Elevated blood cholesterol
- Muscle cramps
- Heavy or irregular menstruation
- Thinning hair
- Slowed heart rate
- Depression
- Impaired memory
However, the severity of symptoms can vary greatly. People with mild hypothyroidism or subclinical hypothyroidism may have minimal symptoms or none at all. Older adults also tend to have more subtle symptoms compared to younger people.
Should High TSH Be Treated?
Whether high TSH requires treatment depends on several factors:
- Your exact TSH level and how far above normal it is
- Presence and severity of hypothyroid symptoms
- Levels of thyroid hormones T3 and T4
- Your age
- Whether you are pregnant
- Presence of goiter or thyroid nodules
- Risk factors like high cholesterol or heart disease
Mild TSH elevations may simply need periodic monitoring, while more significant elevations causing symptoms will usually warrant thyroid hormone replacement medication. Work with your doctor to determine whether your high TSH should be treated or not.
Treatment for High TSH
Treatment for high TSH generally involves thyroid hormone replacement medication to get thyroid hormone levels back to normal. This helps relieve symptoms of hypothyroidism and bring the TSH back down to a healthier range.
Levothyroxine
The standard treatment for hypothyroidism is levothyroxine (Levoxyl, Synthroid, Tirosint, Unithroid). This synthetic version of the T4 thyroid hormone is usually taken once daily by mouth. Your doctor will determine the appropriate dosage based on your weight, age, TSH level, and other factors. It may take several months to adjust the dosage to get your TSH into the optimal range.
Liothyronine
Some doctors may prescribe liothyronine (Cytomel), a synthetic T3 hormone, in combination with levothyroxine. This combination therapy benefits some people who don’t feel well on levothyroxine alone. However, there is limited evidence that combining T3 and T4 is better than T4 alone for most people.
Regular Monitoring
When taking thyroid hormone replacement, your doctor will monitor your TSH and thyroid hormone levels every 6-12 weeks when first starting treatment and adjust the medication dosage as needed. Once the correct dosage is determined and your levels stabilize, yearly monitoring is usually sufficient.
Other Medications
Other prescription medications may be used to treat goiter, thyroid nodules, thyroid cancer, or inflammation of the thyroid. Over-the-counter iodine supplements may benefit people with hypothyroidism related to iodine deficiency.
Lifestyle Changes
Certain lifestyle measures may help complement medical treatment for high TSH:
- Balanced diet: Eat a nutritious diet adequate in iodine, selenium, zinc, iron, and vitamin D.
- Stress management: Find healthy ways to manage stress levels.
- Moderate activity: Get regular moderate exercise. Avoid overtraining.
- Healthy weight: If overweight, lose excess weight through diet and exercise.
- Limit impacts: Reduce factors that impair thyroid function, like smoking, excessive alcohol, and certain medications.
- Supplements: Some supplements like ashwagandha, selenium, zinc, iron, and vitamin D may provide benefit.
A nutritious whole food diet, healthy lifestyle, and stress relief techniques help complement conventional treatment for high TSH.
Can You Have a Normal TSH and Still Have Thyroid Problems?
In most cases, a TSH level within the normal range indicates that thyroid function is optimal. However, there are some exceptions when thyroid issues can still be present despite a normal TSH:
Subclinical Hyperthyroidism
In subclinical hyperthyroidism, TSH is low but circulating thyroid hormones T3 and T4 remain within normal limits. This indicates mild thyroid overactivity that may warrant monitoring and treatment in some cases despite the normal TSH.
Isolated Low T3 Syndrome
Some people with hypothyroid symptoms have a normal TSH with low levels of the active T3 thyroid hormone. Treatment with liothyronine (T3) may help despite the normal TSH.
Thyroid Autoimmunity
People with Hashimoto’s thyroiditis or Graves’ disease may have normal TSH levels but test positive for thyroid antibodies like thyroid peroxidase antibodies or thyrotropin receptor antibodies.
Peripheral Resistance
In some cases, tissues become resistant to the effects of thyroid hormone. This means thyroid hormone levels can’t get into cells efficiently, causing hypothyroid-like symptoms despite normal lab results.
Thyroid Nodules and Goiter
Benign and cancerous thyroid nodules can form and the thyroid gland can enlarge into a goiter, despite a normal TSH. Ultrasound would detect these structural changes.
While not very common, thyroid issues can sometimes still be present even if TSH is within the normal range. A skilled endocrinologist will also assess symptoms and perform additional testing beyond TSH when needed.
Key Takeaways
- In most cases, TSH levels above the normal range indicate hypothyroidism or an underactive thyroid.
- However, some high TSH values at the upper end of normal or related to pregnancy, aging, or subclinical hypothyroidism may still be considered acceptable.
- Persistent elevations in TSH usually warrant treatment with thyroid hormone replacement medication to relieve symptoms.
- Lifestyle measures like a healthy diet, stress reduction, and exercise support medical treatment.
- Rarely, thyroid problems like nodules or inflammation can be present even if TSH is normal.
- Work with your doctor to determine whether your high TSH requires treatment based on your symptoms, thyroid hormone levels, and overall health.
The Bottom Line
Moderately elevated TSH levels may still fall within an acceptable range in some situations. However, persistently high TSH usually reflects an underactive thyroid that will benefit from treatment. Blood tests showing high TSH should prompt a discussion with your doctor about what TSH range is optimal for your unique health status.