The thyroid is a small gland at the front of the neck that produces hormones controlling metabolism, energy production, body temperature, and growth. When the thyroid produces too much or too little hormone, it affects virtually every system in the body.
This test measures three markers. TSH (thyroid stimulating hormone) is produced by the pituitary gland and tells the thyroid how much hormone to make. It is the most sensitive early indicator of thyroid dysfunction. Free T4 (thyroxine) is the main hormone the thyroid releases into the bloodstream. Free T3 (triiodothyronine) is the biologically active form that cells actually use, converted mainly from T4 in tissues throughout the body.
Together, these three markers reveal whether the thyroid is underactive (hypothyroidism), overactive (hyperthyroidism), or compensating for a problem elsewhere in the hormonal feedback loop. A high TSH with low Free T4 is the typical pattern for hypothyroidism. A low TSH with elevated Free T4 or Free T3 points towards hyperthyroidism. Subclinical forms, where TSH is abnormal but T3 and T4 remain in range, are also common and worth identifying.
Common symptoms that prompt thyroid testing include persistent fatigue, unexplained weight changes, sensitivity to heat or cold, hair thinning, mood changes, and changes in heart rate. Women are affected by thyroid conditions more frequently than men, and risk increases with age, family history, and existing autoimmune conditions.
If results suggest a thyroid abnormality, your GP or endocrinologist may recommend further testing such as thyroid antibodies to determine whether an autoimmune process is involved.
This test checks whether your thyroid is producing the right amount of hormone. It can help identify an underactive thyroid (hypothyroidism), an overactive thyroid (hyperthyroidism), or flag that your thyroid is compensating for a hormonal imbalance elsewhere in the system.
