This private blood test measures free triiodothyronine, an active thyroid hormone, used alongside TSH and Free T4 to assess thyroid function. The test costs £71.25, plus a £50 blood-draw fee, with results usually available in 1 day.
You can walk in or book online at 117a Harley Street, seven days a week.
Written by Mr Stephen Lingam. Reviewed by Dr Mohammad Bakhtiar (GMC 4694470) on 28/09/2026.
It measures free triiodothyronine, an active thyroid hormone, used alongside TSH and Free T4 to assess thyroid function.
The test costs £71.25. A separate £50 blood-draw fee applies.
Results are usually available in 1 day.
No GP referral is needed. You can walk in or book online.