Thyroid Blood Tests Explained: TSH, T4, T3 and Antibodies, Palm Beach County, FL

What it involves

The thyroid is a small, butterfly-shaped gland in the front of the neck. Its hormones help control how your body uses energy and affect your breathing, heart rate, weight, digestion, and mood. Thyroid function is measured through blood tests, and your provider chooses which ones to order based on your symptoms and history. This page explains the tests, and the practice's [[thyroid care page|/thyroid-care/]] covers the visits that follow.

Who this is for

• Patients who were told their TSH was high or low and want to understand it
• Patients on thyroid medicine who have regular follow-up blood work
• Patients with tiredness, weight change, or feeling too cold or hot who wonder what a thyroid test would show
• Patients bringing thyroid results from another provider to a first visit

What to expect

• A review of your symptoms, medicines, and history before any test is ordered
• A blood draw from a vein in your arm that takes less than five minutes
• A walk-through of each number once the results are back
• A plan for follow-up tests or visits set by your provider

What a TSH test measures

TSH stands for thyroid-stimulating hormone. MedlinePlus explains that the pituitary gland in the brain makes TSH to tell the thyroid how much hormone to produce. If thyroid hormone in the blood is too low, the pituitary makes more TSH to push the thyroid harder. If it is too high, the pituitary makes little or none. So a high TSH usually points toward an underactive thyroid and a low TSH toward an overactive one.

What a TSH test cannot tell you

MedlinePlus is direct that a TSH test can show whether the thyroid is making too much or too little hormone but cannot show why. It also notes that TSH can run high or low even when the gland is healthy. Because of that, one abnormal number is a reason for a conversation and often a second look, not a diagnosis on its own.

The tests that usually come next

If a TSH result is not normal, MedlinePlus says a provider will probably order other thyroid blood tests to find the cause: Tiredness can come from the blood as well as the thyroid, so a complete blood count is often added to thyroid tests, and the complete blood count explained page describes red cells, white cells, and platelets.

• A T4 thyroid hormone test
• A T3 thyroid hormone test
• A thyroid antibodies test, which helps diagnose an autoimmune thyroid disorder

Two autoimmune conditions behind abnormal results

MedlinePlus names Graves' disease as the most common cause of hyperthyroidism, meaning too much thyroid hormone, and Hashimoto's disease as the most common cause of hypothyroidism, meaning too little. Antibody testing is how a provider tells whether an autoimmune cause is involved.

Symptoms that send people to the test

MedlinePlus lists symptoms on both sides. An overactive thyroid can bring weight loss despite eating more, a rapid or irregular heartbeat, nervousness, trouble sleeping, and shaky hands. An underactive thyroid can bring fatigue, weight gain, sensitivity to cold, dry skin, thinning hair, constipation, and depression. It adds that hypothyroidism develops slowly, so many people do not notice symptoms for months or years. Fatigue and weakness have several possible causes besides the thyroid, including low vitamin D or B12, and the vitamin D and B12 blood tests guide explains when those levels are worth checking. When tiredness is the main complaint, the fatigue and tiredness evaluation guide shows where a thyroid test fits among the other blood tests a provider may consider. Ongoing constipation is another reason a provider may check thyroid function, and the constipation evaluation lists the other conditions NIDDK ties to it. An underactive thyroid is one of the medical conditions MedlinePlus lists behind numbness and tingling, as the numbness and tingling guide explains. Thyroid problems are one of the conditions MedlinePlus ties to ringing in the ears, as the tinnitus guide explains.

Preparing and what to tell your provider

MedlinePlus says you may need to stop certain medicines before a TSH test, so tell your provider everything you take, and do not stop any medicine unless told to. MedlinePlus says you may need to fast only if other blood tests were ordered with it, so follow the fasting blood work guide and confirm with the office. If you take thyroid medicine, MedlinePlus says regular TSH tests check that your dose is right. Hair that sheds more than usual is another reason people ask about thyroid tests, and the hair loss guide lists thyroid disease among the causes MedlinePlus names.

Sources

• MedlinePlus — TSH (Thyroid-stimulating hormone) Test
• MedlinePlus — Thyroid Tests
• NIDDK — Hypothyroidism (Underactive Thyroid)