FT3 testing is not necessary in most thyroid diseases patients.

Type of practice

Laboratory tests

Topic Area


Measurement of serum concentration of thyroid hormones helps confirm the clinical suspicion of thyroid dysfunction and evaluate response to treatment. In daily practice, it is quite common that symptoms be non specific (anxiety, depression, abnormal serum lipids, obesity, palpitations … ) and that the pre-test probability of a thyroid disorder be low. In these cases, it is recommended to measure the TSH only, reserving measurement of FT4 and FT3 to the situations where the TSH results suppressed. The measurement of FT3 is not useful in adjusting dosage in patients on regular replacement with levothyroxine.


1. UK Guidelines for the Use of Thyroid Function Tests (ACB-BTA-BTF), 2006. http://www.acb.org.uk/
2. AACE Medical Guidelines for Clinical Practice for the Evaluation and treatment of Hyperthyroidism and Hypothyroidism.Endocr Pract 2002;8:457-69.
3. AACE/AME Medical Guidelines for Clinical Practice for the Diagnosis and Management of Thyroid Nodules. Endocr Pract 2006; 12: 63-102.
4. Demers LM, Spencer CA. Laboratory medicine practice guidelines: laboratory support for the diagnosis and monitoring of thyroid disease. Clin Endocrinol (Oxf) 2003, 58: 138-40.

Attention. Please note that these items are provided only for information and are not intended as a substitute for consultation with a clinician. Patients with any specific questions about the items on this list or their individual situation should consult their clinician.