Subclinical hypothyroidism
An early, mild form of an underactive thyroid: the TSH is raised but the thyroid hormone (free T4) is still normal. Often symptom-free and found on a routine test, it sometimes needs treatment and sometimes just monitoring.
What it is
Subclinical hypothyroidism is a biochemical stage in which the pituitary has to push harder (a raised TSH) to keep thyroid hormone output normal — so the free T4 is still within range. It sits between fully normal thyroid function and overt hypothyroidism. It is common, especially in women and with age, and is usually picked up on a routine blood test rather than from symptoms, though some people have mild tiredness, low mood, weight change or cold intolerance. The key questions it raises are whether it will progress to full hypothyroidism (more likely with a higher TSH and positive thyroid antibodies), and whether treating it helps — which depends on how high the TSH is, the person's age, symptoms, antibody status and whether they are pregnant or trying to conceive. Because the picture is nuanced, it is a condition of judgement rather than an automatic prescription.
Key lab markers
- TSH — raised, this is the defining abnormality; the degree matters (mildly raised vs above 10).
- Free T4 — normal, which is what makes it 'subclinical'; a low free T4 would make it overt hypothyroidism.
- Anti-TPO antibodies — if positive, autoimmune (Hashimoto's) is the cause and progression to overt disease is more likely.
- Repeat TSH — a single mildly raised TSH is often confirmed 2–3 months later, as it can be transient.
- Lipids — can be mildly affected.
Symptoms
- Often none — found on a routine blood test
- Mild tiredness or low energy
- Low mood
- Feeling the cold
- Mild weight gain
- Dry skin, constipation Symptoms, when present, are mild and non-specific and overlap with everyday life, which is part of why treatment decisions are individualised.
Related lab panels
When to discuss with a doctor
A single mildly raised TSH with a normal free T4 is usually repeated after a couple of months, because it can be temporary. If it persists, the decision to treat depends on the details: treatment is more clearly worthwhile when the TSH is above 10, when thyroid antibodies are positive, when there are symptoms, and especially in pregnancy or when trying to conceive, where even mild thyroid underactivity matters. Milder cases in older adults are often monitored rather than treated. This is a shared decision with your doctor rather than an automatic one. Mediora.AI shows the TSH/free-T4/antibody pattern and flags the level relative to the treat-or-monitor thresholds; the decision belongs with your GP or endocrinologist.