Overview
Subclinical hyperthyroidism is defined as suppressed thyroid-stimulating hormone (TSH) below the normal reference range but free T4 (FT4) and free T3 (FT3) are within the normal reference range.
The most common cause of subclinical hyperthyroidism is toxic multinodular goitre.
Epidemiology
- Subclinical hyperthyroidism is more common in the elderly
Diagnosis and Referral
Diagnosis
Thyroid function tests (TFTs) show low TSH and normal FT4 and FT3. These should be repeated 3 months after to exclude other causes of transient TSH suppression. If after at least 3 months of repeat testing, TSH is still low but FT4 and FT3 are normal, subclinical hyperthyroidism is diagnosed.
Referral
- Urgently refer to secondary care via a suspected cancer pathway if:
- Goitre, nodule, or structural change is present or if malignancy is suspected
- TFTs are generally normal in people with thyroid cancer
- Refer to an endocrinologist if:
- Subclinical hyperthyroidism is diagnosed as above and there is evidence of thyroid disease (e.g. goitre, positive autoantibodies, or symptoms of hyperthyroidism)
Complications
Subclinical hyperthyroidism can have the following complications:
- Atrial fibrillation
- Osteoporosis
- Increased risk of dementia
