Reference ranges
Free T4 reference range
Reference ranges describe the interval a laboratory prints next to your result. They are not a diagnosis of what is “normal” for you personally — your clinician interprets results in context.
General biomarker education — not personalized medical advice. Learn more
What Free T4 measures
Labs report the fraction of thyroxine that is not bound to carrier proteins in the blood.
Why ranges differ
Laboratories set their own reference intervals using their methods, equipment, and population data. That is why the range on your Quest report may differ from a LabCorp report — always use the interval printed on your source document.
Common units
Free T4 is often reported in ng/dL. Confirm units on your original report before comparing values across time.