When to Check Your Thyroid: TSH Basics for Adults Over 40

Medically reviewed by Meg LaFerriere, APRN · Regulate Rx, Lee’s Summit, MO

Your thyroid is small, but it sets the pace for almost everything: energy, temperature, heart rate, digestion and weight. When it’s off, you feel it.

What does TSH actually measure?

TSH comes from the pituitary gland in your brain. It tells your thyroid how hard to work. Think of it as a thermostat signal.

When thyroid hormone is low, the pituitary turns TSH up to push the thyroid harder, so TSH rises. When thyroid hormone is high, TSH drops. That’s why the numbers can seem backward at first: a high TSH usually means an underactive thyroid.

Many labs list a reference range of roughly 0.4 to 4.0 mIU/L, though each lab sets its own. Your clinician reads your result alongside your symptoms and other tests.

What symptoms suggest a thyroid problem?

Thyroid symptoms overlap with stress, aging and other hormone changes, which is why testing helps.

Underactive (hypothyroid)	Overactive (hyperthyroid)
Fatigue and sluggishness	Feeling jittery or anxious
Weight gain or trouble losing weight	Unplanned weight loss
Feeling cold	Feeling hot and sweaty
Dry skin, hair thinning	Fast or irregular heartbeat
Constipation	More frequent bowel movements
Heavier or irregular periods, low mood	Lighter periods, trouble sleeping

Women are much more likely than men to have thyroid disease, and risk rises with age. In the US, the most common cause of an underactive thyroid is Hashimoto’s thyroiditis, an autoimmune condition.

When should you get a TSH test?

Guidelines differ on routine screening for people with no symptoms. Most clinicians agree it makes sense to check when:

• You have symptoms like those above that don’t have a clear explanation
• You have a family history of thyroid disease or another autoimmune condition
• You’re in perimenopause or menopause and your symptoms are hard to sort out
• You’re planning pregnancy, are pregnant or recently gave birth
• You take medications known to affect the thyroid, such as lithium or amiodarone
• You have high cholesterol, infertility or an irregular heart rhythm

What else goes on a thyroid panel?

TSH is the starting point. If it’s out of range, or symptoms are strong, your clinician may add free T4, the main hormone your thyroid makes. Free T3 is sometimes checked too. Thyroid antibodies (TPO antibodies) can show whether autoimmune thyroid disease is likely.

A few things can throw off results. High-dose biotin, common in hair and nail supplements, can interfere with some thyroid tests, so ask whether to pause it before your draw. Recent illness and certain medications can also shift numbers.

If you’re curious how thyroid fits into a broader workup, see our guide to what a comprehensive hormone panel can include, or the women’s program and men’s program pages.

How do thyroid and sex hormones interact?

They overlap more than most people realize. Low thyroid function can cause heavy periods and low libido. Perimenopause can cause fatigue, weight change and mood shifts that look a lot like thyroid trouble. Estrogen therapy taken by mouth can change thyroid-binding proteins, which matters if you already take thyroid medication.

This is why it helps to look at the whole picture. Treating one system while ignoring another can leave you feeling only partly better.

Frequently asked questions

Can my TSH be normal and I still have a thyroid problem?

Sometimes. Early autoimmune thyroid disease, or a problem with the pituitary, can show up in other tests first. If symptoms continue, your clinician may repeat TSH or add free T4 and antibodies.

Do I need to fast for a thyroid test?

Fasting usually isn’t required for TSH alone, but it may be if other labs are drawn at the same time. Ask about pausing biotin supplements for a few days beforehand, since biotin can skew some results.

Does Regulate Rx treat thyroid disease?

Thyroid markers can be part of our hormone lab panel, and Meg reviews them with your other results. If you need specialized thyroid care, we’ll help you connect with the right clinician.

Sources: American Thyroid Association; Endocrine Society; FDA safety communication on biotin and lab tests; Cleveland Clinic; Mayo Clinic; NIH/MedlinePlus

This article is for general education and isn’t medical advice. Treatments aren’t right for everyone, and results vary. Our practitioner reviews your health history before any treatment.