Short answer: SHBG is a protein that binds testosterone in the bloodstream. Looking at SHBG and testosterone together can help explain why a total testosterone result may not match symptoms, especially when SHBG is unusually high or low. The value should be interpreted with properly timed testosterone lab testing and the patient’s overall health.
Total testosterone is often the first laboratory test used to evaluate suspected deficiency. It remains important, but it does not tell the whole story in every patient.
What is SHBG?
Sex hormone-binding globulin is made mainly by the liver. It carries testosterone and estradiol through the blood. Testosterone exists in bound and unbound forms; only a small portion is free.
Changes in SHBG can shift the relationship between total and free testosterone. A man with high SHBG can have a total value that looks acceptable while the estimated free portion is lower. A man with low SHBG may have a low total value without the same degree of reduction in free testosterone.
7 reasons SHBG and testosterone are reviewed together
1. Symptoms and total testosterone do not match
When symptoms strongly suggest deficiency but total testosterone is not clearly low—or when total testosterone is low without a compatible clinical picture—SHBG can provide useful context.
2. The total result is near the lower boundary
A borderline result is particularly sensitive to testing conditions and protein binding. Repeat morning testing and an appropriate free testosterone assessment may help avoid both overdiagnosis and missed diagnosis.
3. Obesity or insulin resistance may lower SHBG
Lower SHBG is often seen with obesity, insulin resistance, and type 2 diabetes. This can pull total testosterone downward and complicate interpretation.
4. Thyroid or liver conditions may alter SHBG
Thyroid status and liver health can affect SHBG production. The direction of change depends on the condition, and abnormal results should be evaluated rather than attributed to hormones alone.
5. Aging can raise SHBG
SHBG often increases with age. The result may help explain why total testosterone and free testosterone tell different stories in an older patient.
6. Certain medications can change SHBG
Estrogens, some antiseizure medications, thyroid hormone exposure, and other drugs may influence SHBG. A complete medication and supplement list is essential for interpretation.
7. It can improve calculated free testosterone
Some clinical calculations use total testosterone, SHBG, and albumin to estimate free testosterone. The method and assay quality matter, so results from different laboratories may not be directly comparable.
High SHBG versus low SHBG
High SHBG can be associated with aging, hyperthyroidism, some liver conditions, estrogen exposure, and certain medications. Low SHBG can occur with obesity, insulin resistance, hypothyroidism, and some medication or hormone exposures. These are examples, not a diagnosis.
The goal is not to “treat the SHBG number” in isolation. The clinician looks for a reversible contributor and determines whether the overall findings support a hormone diagnosis.
How testing is performed
Evaluation usually begins with morning total testosterone. A low result is commonly confirmed on a separate morning. SHBG, albumin, or free testosterone may be added when indicated. Acute illness, severe sleep disruption, recent hormone use, and laboratory method can affect interpretation.
For a broader overview, see our guide to blood tests before TRT.
Frequently asked questions
Does high SHBG mean testosterone is low?
Not automatically. It changes how testosterone is distributed and may reduce the free fraction, but total and free results, symptoms, and clinical context must be reviewed together.
Can SHBG be changed?
Sometimes an underlying condition or medication contributes, but treatment should address the cause rather than chase a target SHBG value without context.
Which free testosterone test is best?
Methods differ. Equilibrium dialysis is considered a reference approach, while calculated free testosterone may be useful when reliable total testosterone, SHBG, and albumin results are available. The clinician should interpret the laboratory’s method.
This article is for general educational purposes and does not replace individualized medical advice, diagnosis, or treatment. Testing and treatment decisions vary by patient.
