What is Subclinical Hyperthyroidism?

TLDR: Subclinical hyperthyroidism is when you have low levels of TSH but have normal levels of T3 and T4.

How can you diagnose Subclinical hyperthyroidism?

If your TSH levels are low and your T4 and T3 levels are in the normal ranges.

Subclinical hyperthyroidism is generally classified into two categories:

Grade I: Low, but detectable TSH. People in this category have TSH levels between 0.1 and 0.4 mlU/L.
Grade II: Undetectable TSH. People in this category have TSH levels less than 0.1 mlU/L.

What is Subclinical hyperthyroidism?

Subclinical hyperthyroidism is a condition in which you have low levels of thyroid stimulating hormone (TSH) but normal levels of the thyroid hormones T3 and T4.

Let’s take a closer look at T3 and T4:

  • T4 (thyroxine) is the major thyroid hormone secreted by your thyroid gland.
  • T3 (triiodothyronine) is a modified version of T4.

Let’s look at TSH:

The amount of T4 produced by your thyroid gland is controlled by the levels of TSH production by your pituitary gland and vice versa. Therefore, if your pituitary gland sees very little T4, it will produce more TSH to tell your thyroid gland to produce more T4. Once the amount of T4 reaches appropriate levels, your pituitary gland recognizes that and stops producing TSH.

So where does subclinical hyperthyroidism come into the picture? An imbalance of hormones:

In people with subclinical hyperthyroidism, the thyroid produces normal levels of T4 and T3. Yet, they have lower-than-normal TSH levels. This imbalance of hormones leads to the condition.

What are the potential symptoms of subclinical hyperthyroidism?

Most people who have subclinical hyperthyroidism have no symptoms of an overactive thyroid. If symptoms of subclinical hyperthyroidism are present, they’re mild and nonspecific.

These symptoms can include:

  • rapid heartbeat or heart palpitations
  • tremors, typically in your hands or fingers
  • sweating or intolerance to heat
  • nervousness, anxiety, or feeling irritable
  • weight loss
  • difficulty concentrating

What can subclinical hyperthyroidism be caused by?

Subclinical hyperthyroidism can be caused by both internal (endogenous) and external (exogenous) factors.

Internal causes can include:

  • Graves’ disease. Graves’ disease is an autoimmune disorder that causes an overproduction of thyroid hormones.
  • Multinodular goiter. An enlarged thyroid gland is called a goiter. A multinodular goiter is an enlarged thyroid where multiple lumps, or nodules, can be observed.
  • Thyroiditis. Thyroiditis is an inflammation of the thyroid gland, which includes a group of disorders.
  • Thyroid adenoma. A thyroid adenoma is a benign tumor of the thyroid gland.

External causes can include:

  • excessive TSH-suppressive therapy
  • unintentional TSH suppression during hormone therapy for hypothyroidism
  • Pregnancy, especially in the first trimester. However, it’s not associated with adverse pregnancy outcomes and typically doesn’t require treatment.

Effects on the body if left untreated:

  • Increased risk of hyperthyroidism. People who have undetectable TSH levels are at an increased risk for developing hyperthyroidism.
  • Negative cardiovascular effects. People who are untreated can develop an increased heart rate, a reduced tolerance to exercise, arrhythmias, atrial fibrillation
  • Decreased bone density. Untreated subclinical hyperthyroidism can lead to a decrease in bone density in postmenopausal women.
  • Dementia. Some reports suggest that untreated subclinical hyperthyroidism can increase your risk of developing dementia.

Whether the condition needs treatment depends on:

  • the cause
  • how severe it is
  • the presence of any related complications

Your doctor will work to diagnose what may be causing your subclinical hyperthyroidism. Determining the cause can help determine the appropriate treatment.

Treating internal causes of subclinical hyperthyroidism:
If you have subclinical hyperthyroidism due to Graves’ disease, medical treatment is required. Your doctor will likely prescribe radioactive iodine therapy or anti-thyroid medications, such as methimazole.

Radioactive iodine therapy and anti-thyroid medications can also be used to treat subclinical hyperthyroidism due to multinodular goiter or thyroid adenoma.

Subclinical hyperthyroidism due to thyroiditis typically resolves spontaneously without any additional treatment required. If thyroiditis is severe, your doctor may prescribe anti-inflammatory drugs. These could include nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids.

Treating external causes of subclinical hyperthyroidism:
If the cause is due to TSH-suppressive therapy or hormone therapy, your doctor may adjust the dosage of these drugs where appropriate.

Treatment based on severity:
If your TSH levels are low but still detectable and you don’t have complications, you may not receive immediate treatment. Instead, your doctor may choose to retest your TSH levels every few months until they return to normal or your doctor is satisfied that your condition is stable.

Treatment may be required if your TSH levels fall into Grade I or Grade II and you’re in the following risk groups:

  • you’re over 65 years of age
  • you have cardiovascular disease
  • you have osteoporosis
  • you have symptoms suggestive of hyperthyroidism

Your treatment will depend on what type of condition is causing your subclinical hyperthyroidism.

Treatment with the presence of complications:
If you’re experiencing cardiovascular or bone-related symptoms due to your subclinical hyperthyroidism, you may benefit from beta-blockers and bisphosphonates.

You may have some weight loss if you have subclinical hyperthyroidism. This is because people with an overactive thyroid have an elevated basal metabolic rate (BMR). The calorie requirements for maintaining your weight will be higher.

Since this condition can be caused by a variety of different conditions, the treatment you receive will depend on the cause and severity. Once your levels return to normal either naturally or through use of medication, your outlook should be excellent.


Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

The information on is NOT intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice.

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