Mildly underactive thyroid

Clinically: Subclinical hypothyroidism · also SCH, mild hypothyroidism, subclinical underactive thyroid, compensated hypothyroidism

endocrine

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, 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

The thyroid control hormone (TSH) is high, but the thyroid hormone itself is still normal. It is a mild, early form of an underactive thyroid.

Raised serum TSH with thyroxine (free T4) and T3 within the population reference range. The 2013 ETA guideline splits it into mildly raised TSH (4.0-10.0 mU/L) and more severely raised TSH (above 10 mU/L); persistent disease means raised TSH with normal free T4 on two occasions at least 3 months apart.

caveats unverified

TSH can rise for a short time for many reasons, such as recovery from an illness. So a high result is repeated after 2 to 3 months before the label is used. TSH also tends to be a little higher in older people.

No clinical version written yet.

The typical lab pattern

What the diagnosis rests on

The results a diagnosis is actually made on.

Thyrotropin

high

—

ETA 2013 definition: TSH above the reference range with normal thyroid hormones; mild 4.0-10.0 mU/L, more severe above 10 mU/L. A raised result is repeated after 2-3 months, and TSH is checked at least yearly once treatment starts.

Consistent with it

Fits the picture, but not enough on its own.

Cholesterol, total	high	ref ≤ 200	Study results are mixed. Some find higher total cholesterol, rising with TSH; one large study found it only in women.
LDL cholesterol (calculated)	high	ref ≤ 100	Study results are mixed. One large study found higher LDL cholesterol only in women.

Points away from it

Results that argue against this explanation.

Thyroxine, free

either

—

Must be within the reference range. A free T4 outside it points to overt thyroid disease instead.

How it usually feels

Difficulty passing stool · occasional
Dry, rough skin · occasional
Feeling cold when others do not · occasional
Feeling tired all the time · occasional
Muscle cramps or spasms · occasional
Muscles feeling weak · occasional
Trouble thinking clearly · occasional

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.