Subclinical hypothyroidism involves high levels of thyroid-stimulating hormone and typical thyroxine levels in the blood. This may be due to an autoimmune disease, a medication, or thyroid surgery. People with this condition may not experience symptoms.
While thyroid hormone levels in a person’s blood will be within the acceptable range, they
Treatment for subclinical hypothyroidism may include the thyroid hormone replacement medication levothyroxine.
This article explores subclinical hypothyroidism, including the causes, symptoms, diagnosis, and treatments.
A person’s pituitary gland produces TSH, which, in turn, stimulates the thyroid gland, a butterfly-shaped organ at the base of the neck. The TSH causes the thyroid to produce thyroid hormones called triiodothyronine (T3) and thyroxine (T4).
Thyroid hormones regulate metabolic processes in the body, including heart rate, digestive function, and brain development.
Healthcare experts call it subclinical hypothyroidism because the free thyroid hormone levels are still normal. Some people do not experience symptoms; however, others can have the same symptoms that overt hypothyroidism would cause.
If the thyroid is not producing enough T4 to meet the body’s needs, TSH levels will spike to overwork the thyroid.
The higher the
Learn more about hypothyroidism and other thyroid conditions.
Subclinical hypothyroidism has several potential causes, including certain autoimmune conditions, surgery, and some medications.
Hashimoto’s thyroiditis, or Hashimoto’s disease
Symptoms may include:
- thyroid gland enlargement, which can cause pain and trouble swallowing
- fatigue and sluggishness
- weight gain
- muscle weakness
- changes to the skin and hair
Treatment for certain thyroid conditions, such as thyroid nodules and thyroid cancer, may involve the surgical removal of part or all of the thyroid. This procedure is known as a thyroidectomy.
Injury to the thyroid gland
Blunt force trauma or injury to the head or neck may reduce the thyroid’s ability to produce enough thyroid hormones to meet the body’s needs. This may lead to subclinical hypothyroidism.
Radioactive iodine or antithyroid medications may cause subclinical hypothyroidism in people who have previously undergone treatment for hyperthyroidism.
According to a review published in the Cleveland Clinic Journal of Medicine, the following medications can affect thyroid function and cause subclinical hypothyroidism:
- iodinated contrast
- tyrosine kinase inhibitors
Learn more about the thyroid and other conditions.
The following factors may increase a person’s chances of developing subclinical hypothyroidism:
- Age: TSH levels increase as people age. People aged
65–70 yearsmay have elevated levels of TSH and low T4 levels.
- Sex: Subclinical hypothyroidism is more common among females than among males. Researchers don’t fully understand why this is the case, but they believe that the female hormone estrogen may be responsible.
- Race: According to a 2019 review, subclinical hypothyroidism is more common in white people. The authors note that this may be due to a genetic factor.
- Iodine intake: Populations that consume excess iodine may be at a higher risk of subclinical hypothyroidism than those that do not.
Before diagnosing this condition, a doctor will rule out non-thyroidal factors that can elevate TSH levels.
Health experts recommend that doctors assess a person’s TSH and T4 levels every 2–3 months.
To make a proper diagnosis, the doctor
- Thyroid function test: This can show the doctor how well a person’s thyroid gland is working. High TSH levels and normal T4 levels suggest subclinical hypothyroidism.
- Thyroid peroxidase antibody (TPO) test: This can help the doctor measure the level of antibodies against blood TPO. Elevated TPO antibodies may indicate Hashimoto’s thyroiditis.
- Ultrasound: An ultrasound can reveal the state and shape of the thyroid. Dark gray patches on an ultrasound may indicate hypothyroidism.
Doctors treat subclinical hypothyroidism with a replacement therapy known as levothyroxine therapy.
The American Thyroid Association (ATA) and the American Association of Clinical Endocrinology
- TSH higher than 10 mIU/L
- presence of hypothyroid symptoms
- presence of cardiovascular risk factors
- positive TPO antibody
For people without a cardiovascular disease, the starting dose of levothyroxine is 1.6 mcg/kg. For people with cardiovascular disease, the starting dose is 25 mcg/kg, and a doctor will increase it as needed.
The ATA notes that pregnant people should take their thyroxine dose as instructed, as it is safe for them to do so.
In fact, most pregnant people need a higher dose of levothyroxine to keep up with the high thyroxine needs of their body and their developing baby.
If a pregnant person has received a diagnosis of subclinical hypothyroidism, they must start treatment immediately and continue it until they deliver.
Subclinical hypothyroidism has an incidence rate of
Without treatment, it can escalate into full hypothyroidism. The risk of subclinical hypothyroidism progressing to hypothyroidism is
In hypothyroidism, the thyroid produces low levels of thyroid hormones.
The ATA notes that hypothyroidism’s symptoms will likely develop slowly over a few months or years. However, some people develop symptoms quickly over a few months. Generally, the lower a person’s thyroid hormone levels and the longer they stay low, the more severe the symptoms will be.
If a person is experiencing even mild symptoms of subclinical hypothyroidism, they should consult a doctor.
A doctor will evaluate a person’s symptoms and determine the best treatment.
Subclinical hypothyroidism is a mild endocrine disorder characterized by normal T4 but high TSH levels.
The condition can be asymptomatic. This means that people with the condition do not know they have it. At other times, it can cause mild or severe symptoms.
Subclinical hypothyroidism can be a result of the autoimmune disease Hashimoto’s thyroiditis, certain medications, or other factors.
To accurately diagnose the condition, a doctor may order a thyroid function test, a TPO antibody test, and an ultrasound.
Levothyroxine therapy is the first line of treatment for people with subclinical hypothyroidism. It can help relieve symptoms and prevent the condition from progressing.