A primary care professional or an endocrinologist can diagnose hypothyroidism. The process typically involves a medical history, physical exams, and blood tests.

Hypothyroidism, or underactive thyroid, is when your thyroid gland doesn’t make enough thyroid hormones. Researchers estimate that up to 7% of people in the United States have undiagnosed hypothyroidism.

Common symptoms of hypothyroidism may include:

  • persistent and unexplained fatigue
  • unintentional weight gain
  • cold intolerance
  • chronic constipation
  • dry skin
  • dry, thinning hair
  • voice changes (hoarse voice)
  • muscle and joint pain
  • puffy face

If you have a combination of the symptoms above, it may be a good idea to discuss them with a healthcare professional. They may recommend blood tests to check your thyroid levels.

If you have symptoms of hypothyroidism, your first stop will likely be your primary care professional. You can discuss your symptoms with them, and they may order tests to help diagnose hypothyroidism.

It’s possible that they may refer you to an endocrinologist. These are doctors who specialize in treating conditions that involve hormones, such as thyroid disease and diabetes.

A doctor may reach a hypothyroidism diagnosis based on your family and personal medical history, a physical exam, and a series of blood and imaging tests.

Medical history

When you first meet with a healthcare professional, they will gather information from medical history. They’ll request paperwork from you and ask you about things like:

  • symptom description, duration, and severity
  • family history of thyroid disease and other conditions
  • current or past medical conditions you’ve had
  • medications and supplements you take

Physical exam

After getting your medical history, a healthcare professional will do a physical exam. During the exam, they’ll gently touch your neck to help get an idea of the size and shape of your thyroid gland.

They may also check your lymph nodes, heart rate, oxygenation, and other important health markers. This will help them reach an accurate diagnosis, which may involve ruling out other symptoms and conditions.

Blood tests

The results of blood tests, which don’t require special preparation, are used to diagnose hypothyroidism. These tests involve collecting a small sample of blood from a vein in your arm and sending it to a lab to be analyzed.

Common thyroid blood tests look at the levels of three hormones:

  • thyroid-stimulating hormone (TSH)
  • thyroxine (T4): Inactive thyroid hormone
  • triiodothyronine (T3): Active thyroid hormone

TSH is a hormone made by the pituitary gland that tells your thyroid to make thyroid hormone. TSH levels are high in hypothyroidism. This is due to the pituitary gland signaling the need for more TSH in response to low levels of thyroid hormones.

The free T4 test measures the amount of thyroid hormone in your body that’s available for use. If you have hypothyroidism, you will likely have low free T4 levels since your thyroid isn’t making enough thyroid hormone.

The free T3 test measures how much T3 you have in the blood that the body’s cells can use for important functions.

High TSH levels and low free T4 and T3 levels signal clinical hypothyroidism.

Subclinical hypothyroidism will be diagnosed if you have high TSH levels and normal free T4 and T3 levels. People with subclinical hypothyroidism may have milder symptoms, and the doctor may want to monitor hormone levels.

Testing for Hashimoto’s thyroiditis

Hashimoto’s thyroiditis is an autoimmune disease that can cause hypothyroidism. In Hashimoto’s thyroiditis, your immune system mistakenly attacks your thyroid gland, which damages it and lowers thyroid hormone production.

If you have hypothyroidism, a healthcare professional may want to see if Hashimoto’s thyroiditis is the cause. This is done using a blood test to look for antibodies to thyroid peroxidase and thyroglobulin, enzymes involved in making thyroid hormone.

Elevated levels of these antibodies suggest that you could have Hashimoto’s thyroiditis.

Since the thyroid is often enlarged in advanced Hashimoto’s thyroiditis, ultrasound may also be used. Ultrasound can help a healthcare professional look at the size of your thyroid and also check for other features associated with Hashimoto’s thyroiditis.

Once your diagnosis of hypothyroidism is confirmed, a doctor may recommend next steps. If you haven’t already, you may be referred to an endocrinologist to help plan and monitor your hypothyroidism treatment.

Hypothyroidism is often treated using a medication called levothyroxine. Since levothyroxine is a synthetic version of the T4 made in your body, it replaces low levels of the natural hormone and helps the body convert T4 to T3 to support essential functions.

If someone can’t take levothyroxine, options are limited but available and may include:

  • liothyroizine sodium (Cytomel): Synthetic T3
  • liotrix (Thyrolar): Synthetic T3 with T4
  • desiccated thyroid extract (Armout Thyroid, NP Thyroid): T4 and T3 from pig thyroid glands

If you’re seeing a healthcare professional for symptoms of hypothyroidism, you may be wondering how to prepare. Try some of the following tips below.

Make a list

Prior to your appointment, it may be helpful to sit down and think about your main questions or concerns. Writing these down can help you remember to address them when you meet with the doctor.

Keep a journal

Hypothyroidism can cause a variety of vague or nonspecific symptoms that may vary from person to person. As such, accurately reporting your symptoms can help your healthcare professional zero in on a diagnosis.

If you’re noticing persistent symptoms that are consistent with hypothyroidism, it can be helpful to track when the symptoms first appeared, how severe they are, and if anything makes them better or worse.

Gather information

During your appointment, you will be asked about your personal and family medical history and any medications or supplements you are using.

Aim to gather this information before you meet with the healthcare team, as it can help them with a diagnosis.

Ask a family member or friend to come

It’s natural to get caught in the moment during a doctor’s appointment and forget one or two things on your list of questions and concerns.

If you’re concerned this may happen to you, ask a trusted friend or family member to come with you. Not only can they help you take notes, but they can also prompt you if you forget to cover something.

Hypothyroidism is diagnosed by a primary care professional or endocrinologist. A medical history, physical exam, and blood tests for TSH, T3, and T4 are used to make a diagnosis. Further tests may be used to check for Hashimoto’s thyroiditis.

Levothyroxine is used to treat hypothyroidism and helps to replace missing thyroid hormone.

If you’re having symptoms that are consistent with hypothyroidism, consider making an appointment with a healthcare professional to talk about them. Hypothyroidism is a treatable condition, and support is available.