Two men jogging while discussing total versus free testosterone

Total versus free testosterone: a closer look

Medically reviewed by Morgan Spicer, Medical Communications Manager on December 12, 2022. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

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When you’re suffering from symptoms like hair growth or loss, fluctuations in body fat distribution, or changes in muscle mass, you may begin to suspect that your testosterone levels may be outside their normal ranges. Read on to go over a few things you should know about the kinds of testosterone tests that are available.

What’s the difference between total testosterone and free testosterone?

You may already know that testosterone is the primary male sex hormone. What you may not know is that it plays an important role for people of all sexes.

In people assigned male at birth, testosterone is produced in the testes. In people assigned female at birth, and to a lesser extent, it is produced in the ovaries. It’s most commonly associated with its effects on sex drive and masculine secondary sexual characteristics (like body hair or a deeper voice), but testosterone is also involved in muscle growth and fat storage and/or breakdown. A testosterone level outside of normal ranges can disrupt signaling to fat and muscle cells, causing them to grow or shrink abnormally—which can translate to weight fluctuation or body fat redistribution.

Total testosterone is the largest biological pool of testosterone which includes about 70% that is bound to sex-hormone binding globulin (SHBG), about 20-30% that is bound to albumin (another circulating protein), and about 1-2% that is not bound to any protein (free testosterone). A healthcare provider may order a free testosterone or total testosterone measurement depending on your symptoms or levels they are trying to check.

Both free and total testosterone are used in varying aspects of clinical practice. Repeat tests of total testosterone are commonly recommended if initial testosterone level measurements are outside of the normal ranges. Total (serum) testosterone is the more broadly accepted analyte within clinical guidelines. Studies support the use of salivary free testosterone as an acceptable assay for screening, and it is also commonly tested for if there is suspicion that the level of total testosterone may be low, which can be associated with several medical conditions [1].

What’s the difference between a testosterone blood test and a saliva test?

Both blood tests and saliva tests are well-established techniques for clinically measuring several biomarkers in people of all sexes, and testosterone is no exception. But there are a few differences between these two testing methods:

  • Sample type - Testosterone is circulated throughout your body by the bloodstream, and a fraction of it enters your saliva. Testosterone blood tests measure testosterone levels in a sample of blood, but saliva tests use a sample of saliva.
  • Collection process - Blood samples are often collected through a blood draw (venipuncture) or fingerstick, while saliva samples require someone to spit into a tube.
  • Units of measure - Blood (total testosterone) tests use nanograms per deciliter (ng/dL). Salivary (free testosterone) tests use picograms per milliliter (pg/mL). For comparison, 1 ng/dL = 10 pg/mL, so the numerical results from two different tests that use different types of samples (and different units of measurement) will look completely different. It doesn’t mean either test is inaccurate.

Testosterone tests: the final verdict

There are a variety of methods to test your testosterone levels, both from the comfort of home and in the clinic or lab. Saliva and blood collections are both valid and used for different aspects of clinical practice, as are the free and total testosterone biomarkers. Whichever method you end up choosing, it’s always best to discuss your results with your healthcare provider to set up next steps that are best for you.

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References

1. Testosterone Levels Test. MedlinePlus. Accessed Decembeer 12, 2022. URL

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