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Free T4

FT4 Free Thyroxine Unbound T4
Serum (SST) pmol/L

About this test

Unbound fraction of thyroxine; the active hormone at tissue level. Tested when TSH is abnormal to quantify degree of hyper/hypothyroidism.

Reference Ranges

Sex Age Range Notes
All ≥ 18 yrs 10 – 22 Adult (varies by assay)

Clinical Interpretation

Low / Decreased
Low — hypothyroidism (primary or central). If TSH is also low, consider central hypothyroidism.
High / Increased
Elevated — hyperthyroidism. If markedly elevated with suppressed TSH, treat urgently.

Related Tests

Free T3
Specimen
Serum (SST)
Reporting Unit
pmol/L
Category
⚗️ Endocrinology

⚠ Clinical Note
Reference ranges are indicative. Always interpret results in the context of the individual patient and local laboratory reference intervals, which may vary.