SHBG is a protein that binds sex hormones in the blood. Its level can help explain why a total testosterone result does not tell the whole story about the amount available to tissues. It does not, by itself, explain fatigue, low desire or a change in training performance.[1]
Total testosterone includes hormone bound to proteins and hormone that is unbound, or free. An SHBG test adds information about that binding context.[1]
Why total and free are different measurements
Two people with similar total testosterone can have different SHBG levels. The total result alone cannot show the exact free fraction. A provider may consider SHBG and an appropriate assessment of free testosterone when the clinical picture calls for it.[1][2]
This is not a reason to treat SHBG as a number that should always be pushed lower. Its result also needs interpretation alongside health history, other results and the method used by the laboratory.
Symptoms are necessary context
The Endocrine Society recommends diagnosing testosterone deficiency only when compatible symptoms or signs occur with clearly and consistently low concentrations. It also recommends confirmation with a repeat morning fasting measurement and further evaluation of the cause when deficiency is established.[2]
A single result, a gym-performance plateau or a comparison with someone else's number does not meet that standard.
Read the whole report
The units, reference interval and type of measurement matter. Results from different laboratories are not always directly comparable, and a reference interval is not a personalized performance target.[3]
Useful context includes why the test was ordered, collection timing, symptoms and medications or supplements. Those details help determine whether another measurement would clarify the issue.
