Total vs. free testosterone: what is the difference?

This guide explains testing in adult men and other adults being evaluated for male hypogonadism. It does not set reference ranges for other populations or targets for hormone treatment.

What do total, free and bioavailable mean?

Total testosterone includes both protein-bound and free testosterone. Free testosterone is the portion not attached to a blood protein. Bioavailable testosterone generally means free testosterone plus testosterone loosely attached to albumin.

Binding is not all alike. Sex hormone-binding globulin (SHBG) holds testosterone tightly; albumin binds it more loosely. Albumin-bound testosterone can detach readily, which is why calling all bound testosterone “inactive” is too simple. Fiers and colleagues explain these distinctions in their laboratory study.

Can total testosterone be normal but free testosterone low?

Yes, higher sex hormone-binding globulin (SHBG) can coexist with total testosterone in range and lower free testosterone. Lower SHBG can produce the opposite pattern: lower total without low free testosterone. These patterns need clinical interpretation, as Endotext explains, rather than a diagnosis from either result alone.

Conditions associated with lower SHBG include obesity, insulin resistance, and an underactive thyroid. An overactive thyroid and some liver diseases can be associated with higher SHBG. Medicines can also affect it. An SHBG result alone does not identify the cause or tell you to change treatment. MedlinePlus: SHBG blood test.

When is a free-testosterone test useful?

Free testosterone may help when total testosterone is near the lower limit or a condition changes SHBG. The Endocrine Society guideline recommends it in those circumstances, using a suitable measurement or calculation. It does not mean everyone needs both tests or a larger hormone panel.

If a report contains only total testosterone, ask what question the clinician was trying to answer and whether the result leaves uncertainty. If both measurements are present, ask how they fit together. You do not need to choose whichever number looks more reassuring or more concerning.

How is free testosterone measured or calculated?

A laboratory can separate unattached testosterone from protein-bound testosterone by equilibrium dialysis, or estimate free testosterone from total testosterone, SHBG and albumin with an appropriate equation. Those approaches differ from a direct analog immunoassay, which the Endocrine Society advises against because it is inaccurate. Check the method in the report or laboratory directory; the word “direct” alone does not identify it.

Why can a calculator disagree with my report?

A calculator can disagree because its equation or input values differ from those used by the laboratory. Calculated free testosterone is an estimate, and Fiers and colleagues found differences between calculation methods when comparing them with equilibrium dialysis. That finding does not establish a personal treatment target.

If an online calculator disagrees with your report, save the details and ask which equation and inputs were used. Repeating the calculation on several websites does not resolve a difference in the underlying methods.

Why do free-testosterone ranges differ?

Free-testosterone ranges depend on the method and the reference population, so no single interval fits every report. An age-specific laboratory interval is an example for that assay, not a universal target for men of that age. Free-testosterone assays are outside the CDC hormone standardization program, as ARUP Consult explains; do not compare a free result with a total-testosterone cutoff.

One laboratory, two age groups: Mayo Clinic Laboratories lists free testosterone at 5.25–20.7 ng/dL (about 0.182–0.718 nmol/L) for males aged 20–24, and 4.06–15.6 ng/dL (about 0.141–0.541 nmol/L) at 50–54. These are selected intervals from its equilibrium-dialysis/LC-MS/MS test, not all-laboratory “normal” bands. Mayo laboratory catalog, checked September 13, 2026.

The nmol/L values are rounded conversions using ng/dL × 0.0347. Free testosterone may instead be reported in pg/mL or pmol/L, so check the unit carefully; use the blood-test guide's explanation of units and ranges before comparing numbers.

For total testosterone, the CDC HoSt program evaluates measurement performance against reference values. Certification concerns assay performance; it does not interpret an individual's symptoms or decide whether treatment is appropriate. You can ask whether the laboratory's total-testosterone method is standardized.

Bring the complete reports to follow-up. Check the test name, units, method, and printed range before treating a change as a trend. These details give the clinician a better basis for comparison.

What should I ask about total and free testosterone?

Ask what uncertainty another test would resolve, how the result was obtained and whether collection conditions need to be repeated. If treatment is being discussed, also ask about fertility and the monitoring plan before deciding what to do.

• What uncertainty would measuring free testosterone help resolve for me?
• Was this result measured or calculated, and which method was used?
• Could my health conditions or medicines be affecting SHBG?
• Do these results need repeating under consistent collection conditions?

The aim is to understand what the tests can tell you before making a care decision. This guide cannot diagnose a testosterone deficiency or determine what level you personally need.

Take the printable appointment checklist to your visit, with space for the questions and next steps you want to remember.