8. Interpretation for Thyroid Function Test
High T4 Normal T4 Low T4
High
TSH
In vivo or in vitro artefact
Pituitary hyperthyroidism
Thyroid hormone
resistance
Subclinical hypothyroidism Primary hypothyroidism
Normal
TSH
As above
Sampling within 6 h of
thyroxine dose
Normal Pituitary or hypothalamic
hypothyroidism
Severe non-thyroidal illness
Low
TSH
Hyperthyroidism Subclinical
hyperthyroidism
Subtle thyroxine
overreplacement
Autonomous functioning
thyroid nodule
Non-thyroidal illness
Pituitary or hypothalamic
hypothyroidism
Severe non-thyroidal illness