Empeiria

Underactive thyroid

Clinically: Hypothyroidism · also underactive thyroid, low thyroid, slow thyroid, Hashimoto

endocrine ICD-10 E03.9 MONDO MONDO:0005420 unverified
This describes what this condition typically looks like. It is not a diagnosis and cannot tell you whether you have it -- patterns overlap, results vary between labs, and the same numbers mean different things in different people. Diagnosis usually rests on Thyrotropin, Thyroxine, free, interpreted alongside symptoms and history rather than read off a report.

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

Your thyroid is not making enough hormone. Your whole body then runs slower than it should. That includes your heart rate, your digestion, and your thinking.

Production by the thyroid gland of too little thyroid hormone to meet the body's needs, most commonly due to Hashimoto's disease, an autoimmune thyroiditis. In primary disease the pituitary keeps releasing TSH, so serum TSH is high; a low T4 also indicates hypothyroidism.

why measured unverified

The symptoms are vague and easy to attribute to stress or ageing, but the blood test is simple and the treatment is usually straightforward.

The symptoms are vague and easy to attribute to stress or ageing, but the blood test is simple and the treatment is usually straightforward.

No clinical version written yet.

caveats unverified

The test result runs in the opposite direction to intuition. A HIGH TSH means an UNDERactive thyroid, because TSH is the signal your brain sends telling the gland to work harder. A short illness can shift the number temporarily, so an odd result is usually repeated once you are well.

The test result runs in the opposite direction to intuition. A HIGH TSH means an UNDERactive thyroid, because TSH is the signal your brain sends telling the gland to work harder. A short illness can shift the number temporarily, so an odd result is usually repeated once you are well.

No clinical version written yet.

How common it is

Common, and several times more so in women. The likelihood rises steadily with age. Autoimmune thyroiditis is the usual cause where iodine intake is adequate.

The typical lab pattern

What the diagnosis rests on

The results a diagnosis is actually made on.

Thyrotropin high — TSH above the reference range is part of the definition, and is usually the first test checked.
Thyroxine, free low — Primary hypothyroidism: TSH above and free T4 below the reference range. A high TSH with normal free T4 is the milder, subclinical form.
Consistent with it

Fits the picture, but not enough on its own.

Triiodothyronine, free low — Low T3 can mean hypothyroidism, but T3 is rarely used to diagnose it because TSH and free T4 pick it up earlier.
Cholesterol, total high ref ≤ 200 Hypothyroidism raises total and LDL cholesterol; people with high cholesterol are advised to be tested for it.

How it usually feels

Frequencies say how often a symptom accompanies this condition — not the other way round. Most people with any of these symptoms do not have this.