What counts as bioavailable testosterone?
Bioavailable testosterone is the share of your testosterone that your tissues can realistically use. MedlinePlus describes the bioavailable test as measuring free testosterone plus testosterone attached to proteins other than SHBG, which in practice means albumin.
It helps to picture three pools in your blood:
| Pool | How tightly it is held | Usable by tissues? |
|---|---|---|
| Bound to SHBG | Tightly | No, not readily |
| Bound to albumin | Loosely | Yes, it can be released |
| Free | Not bound | Yes |
| Bioavailable | Free plus albumin-bound | The usable total |
Total testosterone adds all three together. Free testosterone is the last row alone. Bioavailable sits in between, counting everything except the hormone locked to SHBG.
How is it measured?
Labs reach the number in one of two ways. Some measure it directly by removing the SHBG-bound portion from the sample and measuring what remains. Others calculate it from total testosterone, SHBG and albumin, much like a calculated free testosterone.
Either way, the result depends heavily on method, so reference ranges vary more from lab to lab than they do for total testosterone. Compare your number with the range printed on your own report, and keep repeat tests at the same lab. For context on the total, the Endocrine Society patient guide puts normal adult male total testosterone at roughly 300 to 1,000 ng/dL, depending on age and lab.
When does it add something beyond free testosterone?
Its clearest use is in older men whose SHBG has climbed. The Endocrine Society guideline lists aging among the conditions that raise SHBG, along with liver disease, an overactive thyroid and some seizure medicines. When SHBG is high, more testosterone is locked away, and a total that looks comfortably normal can sit on top of a low usable supply.
In that setting, both free and bioavailable testosterone answer the same core question: how much is actually reaching your tissues? Many clinicians rely on free testosterone, measured or calculated, and the guideline focuses on free testosterone when SHBG is abnormal. Bioavailable can still help as a cross-check:
- When free testosterone sits right on the line and a second view of the same question is useful.
- When albumin is unusual, such as with liver disease, because albumin changes the size of the bioavailable pool.
- When an earlier workup used it, so a repeat keeps the trend comparable.
Our pages on the free testosterone test and free versus total testosterone go further into that choice.
What can a high SHBG hide in an older man?
Take a 68-year-old man with low energy and low libido whose morning total is 420 ng/dL. On the total alone, he looks normal. If his SHBG is high, though, a large share of that 420 is bound, and his bioavailable or free value may fall below the lab’s range.
That does not settle the question by itself. MedlinePlus notes that a high SHBG means less of your total testosterone is available to tissues, but the next step is finding out why SHBG is high and repeating the measurement. Our page on high SHBG with normal testosterone walks through that workup.
What does it mean for a testosterone therapy decision?
A low bioavailable value is one piece of evidence, not a diagnosis. The Endocrine Society diagnoses low testosterone only when symptoms fit and levels are consistently low on repeat early-morning testing, with reversible causes considered first. A low usable testosterone in a man with no symptoms is a reason to monitor, not to treat.
Age also matters to how the result is read. Our page on normal testosterone levels by age explains why a number that is typical at 70 would be unusual at 30.
How Ultimate Male decides whether you need it
Bioavailable testosterone is not one of the four tests in our TRT pre-screening panel, which covers total testosterone, estradiol, PSA and a CBC. Whether it belongs in your workup depends on your SHBG, how close your total and free values sit to the line, your age and how well your symptoms fit the numbers.
If you are curious whether this test makes sense for you, ask on the free 10-minute call, and bring any earlier results that included it. At your consultation in San Gabriel or Downey, a PA-C or MD reviews the full picture and explains which measurement answers your question most clearly. Our preventative blood testing page lists every panel we offer.
