Free vs Total Testosterone, Explained Simply
Two men can have the same total number and feel completely different. The reason is often the part most basic tests don't show.
What this is
Total testosterone measures everything circulating in your blood; free testosterone measures the fraction actually available to your body. This page explains why that distinction matters, how a binding protein called SHBG fits in, and why a "normal" total result doesn't always mean the full picture is normal.
Why it happens
Most testosterone in the blood is bound to proteins and unavailable for use. When binding is high, total can look fine while the usable portion is low, which is why symptoms sometimes persist despite a normal total reading.
Common causes
Differences between free and total levels are influenced by SHBG, age, body fat, thyroid function, and certain medications and health conditions.
Possible paths forward
Asking a provider whether free testosterone should be measured alongside total; interpreting both values together rather than in isolation; and considering the factors that shift binding when results don't match symptoms. Diagnosis and treatment are a provider's role.
Questions worth asking.
These FAQs are meant to help you with common situations affecting our community - men over 40 - so when you do speak with your doctor, you have a head start. FAQs are for educational purposes only and aren't a substitute for professional medical advice.