Short answer: Total testosterone is all the testosterone in your blood, both the part attached to proteins and the part floating free. Free testosterone is the small unbound share, only about 1 to 3% of the total, that can move straight into tissues. Doctors start with a morning total testosterone test and add free testosterone when the total is borderline or when a binding protein called SHBG is likely to be unusually high or low. Neither number diagnoses anything on its own: your symptoms, repeat tests and a clinician’s judgment decide what the results mean.
Key Takeaways
- Testosterone travels in three forms: tightly bound to SHBG (about 45% in men), loosely bound to albumin (most of the rest), and free (about 1 to 3%).[3]
- Total testosterone is the standard first test. A widely used harmonized range for healthy young men is about 264 to 916 ng/dL.[5]
- Free testosterone matters most when SHBG is abnormal, because total and free testosterone track closely and only diverge when binding proteins change.[6]
- Equilibrium dialysis is the reference method for free testosterone. A calculation from total testosterone and SHBG is a practical alternative, while “direct” analog immunoassays are considered unreliable.[6][7]
- Test in the morning, usually between 7 and 10 a.m., and expect a repeat test before any diagnosis.[1]
What Total and Free Testosterone Actually Measure
Testosterone does not float around your bloodstream on its own. Most of it is carried by proteins, mainly sex hormone-binding globulin (SHBG) and albumin.[1] That binding acts like a reservoir: it limits how quickly the body can use the hormone and keeps levels steady.
The three forms of testosterone
- SHBG-bound testosterone. SHBG is a protein made by the liver that grips testosterone tightly. In men, roughly 45% of circulating testosterone is held this way.[3] Because the bond is so strong, this fraction is considered biologically inactive.[4]
- Albumin-bound testosterone. Most of the remaining testosterone is loosely attached to albumin.[3] This bond releases easily, so albumin-bound testosterone is treated as available to tissues. Labs sometimes call it “weakly bound.”[4]
- Free testosterone. Only about 1 to 3% is completely unbound.[3] This is the fraction that can diffuse into cells and interact with receptors.[4]
Where “bioavailable” testosterone fits
You may also see bioavailable testosterone on a lab menu. It equals free testosterone plus the albumin-bound portion, in other words everything that is not locked to SHBG.[1] It is ordered less often than total or free testosterone, and some labs note it gives much the same information as a calculated free testosterone value.[3]
Free vs Total Testosterone: Side-by-Side Comparison
The table below uses reference figures published by specific labs and by the Endocrine Society. Every lab sets its own range based on its method, so always compare your result with the range printed on your own report.[2]
| Feature | Total testosterone | Free testosterone | Bioavailable (free + weakly bound) |
|---|---|---|---|
| What it includes | SHBG-bound, albumin-bound and free | Unbound hormone only | Free plus albumin-bound |
| Share of total | 100% | About 1 to 3%[3] | 9 to 46% (Mayo Clinic Laboratories adult male range)[4] |
| Example adult male range | 264 to 916 ng/dL (harmonized range)[5] | 52 to 280 pg/mL, or 1.5 to 3.2% free (Labcorp, equilibrium dialysis)[8] | 40 to 250 ng/dL (Mayo Clinic Laboratories)[4] |
| How often ordered | Most common first test[1] | Follow-up test | Not commonly done[1] |
| Most useful when | Screening for symptoms of low or high testosterone | Total is borderline or SHBG is abnormal | Similar situations to free testosterone |
| Strongly affected by SHBG? | Yes | Much less, which is why it clarifies results | Less, since SHBG-bound hormone is excluded |
Note the units. Total testosterone is usually reported in nanograms per deciliter (ng/dL), while free testosterone is often reported in picograms per milliliter (pg/mL), a much smaller unit. Mixing them up is a common source of panic when people read their own results. For a fuller look at age and population ranges, see our guide to normal testosterone levels.
How Labs Measure Free Testosterone
Free testosterone is harder to measure than total testosterone because it exists in such tiny amounts. The method your lab uses changes how much weight you can put on the number.
Equilibrium dialysis (the reference method)
In equilibrium dialysis, serum is placed against a membrane that lets only unbound hormone pass through. The lab measures the percentage that crosses and multiplies it by total testosterone, which is itself measured by liquid chromatography with tandem mass spectrometry in high-quality labs.[8] A review summarized by the Endocrine Society calls equilibrium dialysis the reference method, but notes it is not readily available everywhere and is not fully standardized between labs.[6]
Calculated free testosterone
When total testosterone and SHBG are measured together, a lab can estimate free testosterone with a formula.[3] In a well-known evaluation by Vermeulen and colleagues, calculated free testosterone gave values almost identical to equilibrium dialysis in the conditions studied, except during pregnancy, and the authors described it as a simple, reliable index for routine use.[7] Because it depends on an accurate SHBG result, a calculated value is only as good as the inputs.
Direct analog immunoassays
Some labs still offer a quick “direct” free testosterone immunoassay. The same Vermeulen evaluation found it returned only a fraction of the true value, and that fraction varied with SHBG.[7] The Endocrine Society review states these assays are inaccurate and should not be used.[6] If your report says “direct” or “analog,” ask your doctor whether a dialysis or calculated value would be more meaningful.
Free androgen index
The free androgen index (FAI) is simply total testosterone divided by SHBG.[3] It is a rough ratio rather than a true free testosterone value, and free androgen calculations are generally not recommended as first-line tests.[3]
When Free Testosterone Matters: The Role of SHBG
For most men, total and free testosterone move together. They only tell different stories when binding proteins change.[6] That is the core reason doctors add a free testosterone test.
Conditions that can raise SHBG
Higher SHBG soaks up more testosterone, so total testosterone can look normal while free testosterone is low. Lab Tests Online lists liver disease, hyperthyroidism, anorexia and estrogen use as causes of higher SHBG.[3] SHBG also rises with age.[4] We cover this situation in detail in our article on high SHBG in men.
Conditions that can lower SHBG
Lower SHBG has the opposite effect: total testosterone can look low while free testosterone is adequate. Causes include obesity, hypothyroidism, androgen use and Cushing’s disease.[3] Some anticonvulsant medicines also affect SHBG.[3]
The practical rule
The Endocrine Society review summarized it this way: measure total testosterone first, and if SHBG changes are suspected or total testosterone sits near the low end of normal, measure free testosterone, ideally by equilibrium dialysis.[6] The 2018 Endocrine Society guideline also puts greater emphasis on free testosterone than its earlier version and calls for accurate, standardized testosterone assays.[5]
How to Get a Reliable Result
Testosterone follows a daily rhythm, peaking in the morning, so timing matters as much as the method.[1]
- Book a morning draw. Blood is usually taken between 7 and 10 a.m., when levels are typically highest.[1]
- Ask about fasting. Some providers ask you to fast for several hours beforehand.[1][2]
- List every medicine and supplement. Some drugs and hormone products affect results, and your provider may ask you to pause certain medicines. Never stop a prescription on your own.[1]
- Expect a repeat test. The case examples in the Endocrine Society guideline use early-morning fasting samples drawn on two different days.[5] A single low value is not a diagnosis.
- Ask which method was used. Equilibrium dialysis or a calculated value is more trustworthy than a direct analog assay.[6][7]
What Your Results May Mean, and When to See a Doctor
A testosterone test alone cannot diagnose a condition, and abnormal results do not always mean treatment is needed.[1] Interpretation depends on your age, symptoms, other test results and overall health. Common patterns include:
- Normal total, normal free: testosterone is unlikely to explain your symptoms. Other causes such as sleep, mood, thyroid or medication effects are worth exploring.
- Normal total, low free: often points to high SHBG. Your doctor may look for the cause, such as thyroid or liver issues.
- Low total, normal free: often seen when SHBG is low, for example with obesity. The free value can prevent a misleading label of low testosterone.
- Low total, low free: warrants a full evaluation. MedlinePlus lists possible causes in men including testicular problems, pituitary disorders, chronic liver or kidney disease, alcohol use disorder and genetic conditions.[1]
See a clinician if you have persistent symptoms such as low sex drive, fatigue, loss of muscle or mood changes. Our guide to the signs of low testosterone explains what to track before your appointment. Only a doctor can confirm a hormone problem and decide whether any treatment is appropriate.
Where Supplements Fit
No supplement replaces a proper workup, and you should tell your doctor about anything you take before a hormone test so it can be factored into your results. Ultra Bann is a natural male vitality supplement made by DL Bioproducts, with seven botanicals listed by amount on the label and no proprietary blend. It is not a medicine, it is not intended to diagnose or manage any medical condition, and it is not a substitute for testing or clinical care. You can review the full Ultra Bann ingredient label to share with your doctor, or learn more on the Ultra Bann shop page.
Frequently Asked Questions
Is free testosterone more important than total testosterone?
Not in every case. Total testosterone is the standard first test, and for most men the two values move together. Free testosterone becomes more important when SHBG is abnormal or when total testosterone is borderline, because then the two numbers can disagree.[6]
What is a normal free testosterone level for men?
It depends on the lab and the method. Labcorp’s equilibrium dialysis test, for example, lists 52 to 280 pg/mL (1.5 to 3.2% free) for adult males.[8] Other labs use different ranges, so always read your result against the range on your own report.
Can total testosterone be normal while free testosterone is low?
Yes. When SHBG is high, more testosterone is tied up in the bound form, so the total can look normal while the free fraction is low. Higher SHBG is linked to aging, liver disease, hyperthyroidism and estrogen use.[3][4]
Why does the time of my blood test matter?
Testosterone is typically highest in the morning, so most labs draw blood between 7 and 10 a.m.[1] An afternoon sample can read lower and lead to a false impression of low testosterone.
Should I get my free testosterone tested by a direct immunoassay?
Experts advise against relying on direct analog immunoassays because they underestimate free testosterone in a way that varies with SHBG.[6][7] Ask for equilibrium dialysis or a calculated free testosterone based on total testosterone and SHBG.
References
- MedlinePlus, U.S. National Library of Medicine. Testosterone Levels Test.
- Cleveland Clinic. Testosterone Test.
- Lab Tests Online UK. Sex Hormone Binding Globulin (SHBG).
- Mayo Clinic Laboratories. Testosterone, Free and Weakly Bound, With Total Testosterone, LC-MS/MS.
- Endocrine Society. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline (2018 presentation).
- Endocrine News, Endocrine Society. Summary of an Endocrine Reviews article by Jasuja and colleagues on free testosterone measurement.
- Vermeulen A, Verdonck L, Kaufman JM. A Critical Evaluation of Simple Methods for the Estimation of Free Testosterone in Serum. Journal of Clinical Endocrinology and Metabolism, volume 84, issue 10.
- Labcorp. Testosterone, Free, Mass Spectrometry/Equilibrium Dialysis (Endocrine Sciences).
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease. This article is for information only and is not medical advice.
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