A thyroid function test is a blood test measuring TSH and, where needed, the thyroid hormones T4 and T3. It detects an underactive thyroid, which can cause weight gain, fatigue, low mood and hair thinning, and an overactive thyroid, which can cause weight loss and palpitations.
In Australia, the test is Medicare rebateable when clinically indicated and can be ordered through a telehealth consultation, with collection at a local pathology centre. Results guide treatment or specialist referral where required.