Doctors diagnose hypothyroidism using a range of blood tests, including TSH and T4 tests. Several scans, such as ultrasound, thyroid, and radioactive iodine uptake scans, also support a diagnosis.

The thyroid is a small gland in the neck that produces thyroxine (T4) and triiodothyronine (T3), two hormones vital for managing the body’s energy use. Hypothyroidism occurs when the body does not make enough of these, which can lead to subtle symptoms, including weight gain, high cholesterol, fatigue, and low mood.

As these are signs of many other health concerns, diagnosing hypothyroidism might be difficult. However, several causes can lead to hypothyroidism, including treatment side effects, cancers, and autoimmune disorders. Getting the right diagnosis can help people access medication for hypothyroidism, which they may need on a lifelong basis.

This article explains the diagnosis process of hypothyroidism. It also goes over the symptoms and treatment for the condition.

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Diagnosis of hypothyroidism starts with questions about a person’s medical and symptom history. Some of the key symptoms of low thyroid hormones may not show for everyone with the condition.

The healthcare professional will typically also ask about previous treatments and surgeries, as well as family history. They may also check previous adverse outcomes for pregnancies and newborns, as well as psychological and cognitive symptoms, including depression, anxiety, and memory loss.

A physical examination will then take place. The healthcare professional will likely look for the following symptoms:

Symptoms may not be obvious at this stage. Only blood tests can demonstrate low thyroid levels.

Learn more about hypothyroidism.

Once a healthcare professional believes the thyroid gland may not be functioning properly, they will usually request blood tests to confirm a low level of thyroid hormones. These tests check hormone levels that fluctuate depending on whether the thyroid is producing enough hormones. Blood tests for hypothyroidism include the following:

  • Thyroid-stimulating hormone (TSH): This is often the first blood test a doctor requests. The pituitary gland — a small gland at the base of the brain — releases TSH to try to increase thyroid hormone levels. If levels are high, the thyroid is not making enough hormones. An abnormal TSH result typically leads to other tests to find the cause.
  • T4: T4 is a thyroid hormone. Low levels can indicate thyroid issues, although low T4 can also occur after severe illness or the use of corticosteroid medications. These affect a type of T4 called “bound” T4 that connects to proteins in the blood, ready for later use. Free T4 is available to enter cells in the body. Healthcare professionals prefer to test free T4 for hypothyroidism diagnosis.
  • Thyroid antibody tests: These can point to an autoimmune disorder that triggers the release of cells to attack an otherwise healthy thyroid. Thyroid antibody tests can help healthcare professionals diagnose Hashimoto thyroiditis, the most common condition that leads to hypothyroidism.

Find out about at-home thyroid tests.

Several scans and imaging tests can help healthcare professionals identify physical issues with the thyroid, such as lumps. These include the following:


An ultrasound technician may use a device that bounces sound waves off the neck to create images of the thyroid. This can show whether lumps have a risk of being cancerous.

Thyroid scan

A thyroid scan shows the shape, size, and position of the thyroid and helps healthcare professionals check for nodules and lumps. The medical team injects a radioactive form of iodine, which the thyroid absorbs. A special camera then takes pictures of the thyroid. Thyroid nodules take up too much iodine, which is shown in the images.

Recognizing the symptoms of hypothyroidism is the first step of the diagnosis process. These may include:

  • extreme tiredness
  • unexpected or unwanted weight gain
  • an inability to tolerate the cold
  • muscle and joint pain
  • dry skin
  • thinning hair
  • irregular or heavy periods
  • fertility problems
  • a slow heart rate
  • depression

These symptoms may vary between individuals and are often quite subtle. Symptoms can also occur due to many other conditions that do not involve thyroid hormone levels. For example, iron deficiency anemia, depression, and sleep apnea may all cause fatigue.

Learn about how hypothyroidism affects the body.

The main treatment for hypothyroidism is a daily oral medication called levothyroxine. This is a lab-made form of T4 that fulfills the same function as thyroid hormones in the body. A person with low thyroid hormones will need to take this for the rest of their life.

Part of diagnosis is working out the ideal dose to correct levels. Doctors may prescribe a lower dose to start the treatment journey before increasing this over time. They will continue to monitor bodily changes, symptoms, and possible side effects, administering blood tests every 6 to 8 weeks to test levels and adjust the dose.

Symptoms may not improve for several months. However, some people start to feel better sooner.

The following are answers to some questions people frequently ask about hypothyroidism diagnosis.

Is hypothyroidism hard to diagnose?

Hypothyroidism might be hard to spot early on due to its subtle symptoms and the multiple possible causes of them. However, blood tests can confirm thyroid hormone levels and further testing can help healthcare professionals identify the underlying cause.

How do I know if I have hypothyroidism without a test?

Confirming hypothyroidism without a test is not possible, as its symptoms can occur due to other conditions. Often, symptoms also develop slowly, so a medical issue may not be obvious. Consult with a healthcare professional if the following symptoms become consistent:

  • fatigue
  • cold sensitivity
  • unexpected weight gain
  • depression
  • constipation
  • slow thinking processes
  • slow movements
  • muscle weakness, cramps, and aches
  • dry, scaly skin
  • low libido
  • carpal tunnel syndrome
  • changes to the volume or frequency of menstruation

Healthcare professionals diagnose hypothyroidism by exploring an individual’s medical history, performing a physical examination, and ordering blood tests. These tests show levels of different hormones that indicate especially low thyroid activity, as well as autoimmune activity that may suggest conditions such as Hashimoto thyroiditis.

The healthcare professional may also request ultrasound and thyroid scans to check for nodules and physical changes to the thyroid. However, the condition can be difficult to diagnose, as symptoms are often subtle and might occur due to several different health problems.