low TSH, raised free thyroid hormones
Last reviewed 06/2021
A depressed TSH with elevated free T3 or T4 is characteristic of primary hyperthyroidism. In most cases the radioiodine thyroid scan will show increased signal.
The common causes of primary hyperthyroidism are:
- Grave's disease:
- 90% have antithyroid antibodies
- diffuse uptake on an radioiodine scan
- multinodular goitre
- toxic nodule
Other diagnoses to consider are:
- transient thyroiditis:
- may be subacute, silent or post-partum
- usually a short history
- rapid return to euthyroidism with treatment
- De Quervain's thyroiditis:
- raised ESR and a tender thyroid are supportive