Thyroid
Free T4: what it measures and why lifters track it
Usually reported in ng/dL by US labs. Check the unit on your own report before comparing two results.
What it is
Free T4 is the main hormone the thyroid makes, in its unbound form. The body turns it into the active T3 as needed.
Why lifters track it
It is read with TSH and free T3 to see where in the chain a change is happening.
What can change the reading
- Biotin supplements can upset the test.
- Some medicines.
Questions for your doctor
What a result means for you is a question for your own doctor. These are worth taking with you:
- How do my TSH, free T4 and free T3 fit together?
Where is my number?
Every lab prints its own range next to each result, and ranges differ between labs and methods. That printed range is the one to compare with, which is why this page gives none. If a result sits outside it, talk to your doctor.
Before your next test
- Follow your lab's or your doctor's instructions first. Most say to fast overnight (water is fine) for blood sugar, insulin and cholesterol.
- Book an early-morning draw, and keep the same time of day every test. Several hormones, testosterone among them, change through the day.
- Skip hard training for a couple of days before. A heavy session can raise AST, ALT, creatinine and hs-CRP for days.
- Drink water as normal. Being dehydrated makes your blood more concentrated, which pushes up hematocrit and hemoglobin.
- If you take biotin (vitamin B7, common in hair and skin supplements), tell your doctor and lab before the test. It can upset the results of many hormone and thyroid tests.
- Use the same lab and the same tests each time where you can. Different methods give different numbers for the same blood.
- Write down anything unusual: a cold, a bad night's sleep, alcohol, a big change in diet or training. It explains a lot when you look back.
Read it with
Coaching built around your blood tests
With CoachAk Full Panel, you add your results to the CoachAk app, see each marker's trend, and every 12 weeks CoachAk reviews your latest test with you and adjusts your training and nutrition around it.
See Full PanelCoaching feedback, not medical advice. CoachAk is not a doctor and does not diagnose or treat conditions. Review all results with your doctor.