Notes · Endocrine · 6 min read
Thyroid function tests made simple
Read TSH and free T4 together and the pattern names the problem.
Key points
- High TSH with low free T4: primary hypothyroidism.
- Low TSH with high free T4 or T3: primary hyperthyroidism.
- High TSH with normal free T4: subclinical hypothyroidism.
- Low or normal TSH with low free T4: secondary (pituitary) hypothyroidism or non-thyroidal illness.
- Biotin supplements can falsely distort some immunoassays; stop them before testing.
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