Subclinical hypothyroidism

Subclinical hypothyroidism is a blood-test finding rather than a clearly symptomatic condition. The pituitary is working a little harder than normal (raised TSH), but the thyroid is still producing enough free T4 to keep it within the reference range.

Many people with subclinical hypothyroidism have no symptoms at all, or only mild ones. Some experience fatigue, feeling cold, or low mood - though these are non-specific and may have other causes.

In the UK, NICE guidance distinguishes between a mildly raised TSH (roughly 4 - 10 mIU/L) and a more significantly raised TSH (above 10 mIU/L). Where TSH is persistently 10 mIU/L or higher (on two tests about three months apart), NICE advises considering levothyroxine. At the lower end - above the reference range but under 10 - regular monitoring is often appropriate, though a time-limited trial of levothyroxine may be offered if there are symptoms, particularly in people under 65.

Whether or not to start levothyroxine is a nuanced decision involving TSH level, symptoms, age, presence of TPO antibodies, and other factors. This is a conversation to have with your GP, who will weigh up the options with you based on your individual picture.