Which result should guide a TRT decision?
Total testosterone should, in most men. It is measured accurately, it is what the diagnostic cutoffs are built on, and two early-morning values settle most cases. Free testosterone earns a say when the total is borderline or when something is pushing SHBG up or down, and then it can tip the decision either way.
Think of total testosterone as the headline and free testosterone as the fine print you read when the headline is ambiguous.
Free and total testosterone side by side
| Total testosterone | Free testosterone | |
|---|---|---|
| What it measures | All testosterone in blood: bound and unbound | Only the unbound fraction available to tissues |
| How it is measured | Immunoassay or mass spectrometry | Equilibrium dialysis, or calculated from total, SHBG and albumin |
| Accuracy | High in a good lab | Depends heavily on method |
| Guideline role | First test, repeated to confirm | Tie-breaker for borderline totals or abnormal SHBG |
| Affected by SHBG | Strongly | Accounts for it |
| Needed every time | Yes | Only in specific situations |
What does each number measure?
Total testosterone
Most testosterone in your blood rides on proteins. A large share is held tightly by sex hormone-binding globulin (SHBG), more is bound loosely to albumin, and only a small fraction floats free. MedlinePlus describes the total test as measuring both bound and free forms, and it is the most common testosterone test ordered. Our total testosterone blood test page covers reference ranges, which vary by lab.
Free testosterone
Free testosterone is the unbound portion that can move into cells. Because total testosterone cannot tell bound from unbound, as the MedlinePlus SHBG page explains, two men with identical totals can have different amounts of usable hormone if their SHBG differs.
Why the free testosterone method matters
Free testosterone is easy to report and hard to measure well. The Endocrine Society guideline recommends getting it by equilibrium dialysis, the reference method, or by estimating it with an accurate formula from total testosterone, SHBG and albumin. The direct analog immunoassays still offered by some labs are considered inaccurate and should not drive a treatment decision.
Here is why. Equilibrium dialysis physically separates free hormone from bound hormone before measuring it. A calculated value applies well-tested binding math to accurately measured inputs. A direct analog assay tries to measure the free fraction in one step and is known to misread it, especially when SHBG is abnormal, which is exactly when you need it to be right. Our free testosterone calculator page shows how the calculation works.
When does free testosterone settle a borderline total?
Guidelines give free testosterone a role in two situations.
A total near the lower limit of normal. If your morning totals hover around the cutoff and your symptoms fit, a reliable free testosterone can show whether usable hormone is truly low. The AUA guideline does not use free testosterone as the primary diagnostic test, but it allows it to help in highly symptomatic men with low-normal or equivocal totals.
A condition that shifts SHBG. Obesity, type 2 diabetes and insulin resistance tend to lower SHBG, which can make a total look low while free testosterone is fine. Liver disease and an overactive thyroid tend to raise SHBG, which can make a total look normal while free testosterone is low. In both cases the free value, measured properly, is the better guide. Our pages on SHBG and high SHBG with normal testosterone go further.
Medicines can move SHBG as well. Anabolic steroids and steroid medicines tend to push it down, while estrogens and some older seizure medicines tend to push it up, so bring a full medicine and supplement list to your visit.
Even then, free testosterone is repeated rather than trusted once, and it never replaces the symptom picture.
Questions to ask about your own report
- Was the total measured in the early morning, and has it been repeated?
- Is free testosterone listed, and does the report say “calculated” or “equilibrium dialysis”?
- Was SHBG measured in the same sample?
- Is the reference range on the report for adult men, and from the same lab as your earlier results?
Practical points: side effects, convenience and cost
Both come from the same morning blood draw, so adding free testosterone means no extra needle. A calculated free testosterone requires SHBG and albumin in the same sample, which is the usual approach. Equilibrium dialysis is often sent to a specialty lab and can take longer.
Free testosterone and SHBG add modestly to lab cost and are ordered when they can change your plan. Lab work at Ultimate Male is direct-pay with a quote before booking, and it is FSA and HSA eligible.
How we read your results
Your first draw at our San Gabriel or Downey clinic is the TRT pre-screening panel: total testosterone, estradiol, PSA and a CBC, bundled with your first consultation. If the total is borderline or your health history suggests SHBG is off, your provider adds SHBG and a calculated free testosterone, and LH and FSH when the source of the problem matters. If an earlier free testosterone came from a direct assay, expect it to be rechecked with a calculated method before anyone draws conclusions from it.
Your PA-C or MD then puts the numbers next to your symptoms and explains what they mean for you, including when the answer is to wait, retest or look elsewhere. For the cutoffs themselves, see what testosterone level qualifies you for TRT, and for the full lab lineup, our preventative blood testing page.
