Your lab report says your testosterone is "normal." You still feel exhausted, foggy, and flat. Or the opposite happens: your total testosterone looks low, your doctor talks about treatment, but something doesn't add up. Both situations usually come down to one overlooked number on the page. That number is SHBG, and it controls how much of your testosterone you can actually use.
This guide breaks down the difference between free and total testosterone, explains what SHBG does, and shows you how to read your own labs the way an endocrinologist would. No hand-waving. Just the numbers, the thresholds, and the traps.
Medical disclaimer: This article is for education only. It is not medical advice and does not replace a conversation with a licensed clinician. Testosterone deficiency is diagnosed by a doctor using your symptoms plus confirmed lab results, not by a single number on a website. Don't start, stop, or change any treatment based on what you read here.
Quick Answer
- Total testosterone is every bit of testosterone in your blood added together. Free testosterone is the tiny slice (roughly 1–4%) that floats unbound and can actually enter your cells and do its job.
- SHBG (sex hormone-binding globulin) is a protein that grabs onto testosterone and holds it hostage. The more SHBG you have, the less free testosterone you have, even if your total looks fine.
- The standard healthy range for total testosterone in men ages 19–39 is 264 to 916 ng/dL, based on a 9,054-man study used to set modern lab reference ranges (Travison 2017).
- If your total testosterone is borderline or your symptoms don't match your total number, always check SHBG and free testosterone. That's exactly when guidelines say total alone can mislead you (Endocrine Society 2018).
What Is the Difference Between Total and Free Testosterone?
Total testosterone is the headline number. When a lab measures it, it counts every molecule of testosterone in your bloodstream, no matter what that molecule is doing. Most of those molecules are not free agents. They're tied up.
Here's how the total breaks down for a typical man:
| Fraction | Roughly how much | Can your cells use it? |
|---|---|---|
| Bound tightly to SHBG | ~40–60% | No. Locked away. |
| Bound loosely to albumin | ~40–50% | Sort of. Releases easily, counts as "bioavailable." |
| Free (unbound) | ~1–4% | Yes. This is the active hormone. |
Free testosterone is the fraction that isn't attached to any protein. It can slip into your tissues, hit androgen receptors, and produce the effects you associate with testosterone: muscle, libido, energy, mood, bone strength. The albumin-bound portion releases easily too, so doctors sometimes group free plus albumin-bound testosterone together and call it bioavailable testosterone.
The key idea: your body doesn't respond to your total testosterone. It responds to what's free. Two men can have the exact same total number and feel completely different, because one has most of it locked up and the other doesn't.
What Does SHBG Actually Do?
SHBG stands for sex hormone-binding globulin. Your liver makes it, and its job is to carry sex hormones (testosterone and estrogen) around your bloodstream. Think of SHBG as a fleet of taxis. Testosterone is the passenger. A passenger sitting in a taxi can't get out and work. Only the passenger standing on the curb (free testosterone) can.
This matters because SHBG isn't a fixed number. It swings up and down based on your age, body weight, blood sugar, thyroid, liver, and the medications you take. When SHBG rises, it pulls more testosterone into "taxis," and your free testosterone drops, even if your total stays the same. When SHBG falls, it releases testosterone, and your free fraction goes up.
That's the whole reason this article exists. SHBG is the dial that decides how much of your total testosterone you actually get to use.
What Pushes SHBG Up?
Higher SHBG means lower free testosterone. These tend to raise it:
| Factor | Effect on SHBG | Why it matters |
|---|---|---|
| Aging | Rises ~1% per year | Free testosterone falls faster than total as you age |
| Hyperthyroidism (overactive thyroid) | Raises | Thyroid hormone tells the liver to make more SHBG |
| Liver disease / cirrhosis | Raises | Disrupted liver hormone handling |
| Estrogen (oral estrogen, some conditions) | Raises | Estrogen drives SHBG production |
| Anorexia / very low body fat | Raises | Linked to metabolic stress |
| Anticonvulsant medications | Raises | Drug effect on the liver |
Because SHBG climbs with age, older men often see free testosterone drop steeper than total testosterone. A 70-year-old can have a "decent looking" total and a genuinely low free level (Travison 2017).
What Pushes SHBG Down?
Lower SHBG means more free testosterone gets released. These tend to lower it:
| Factor | Effect on SHBG | Why it matters |
|---|---|---|
| Obesity | Lowers | Fat tissue and inflammation suppress SHBG |
| Insulin resistance / type 2 diabetes | Lowers | High insulin tells the liver to make less SHBG |
| Hypothyroidism (underactive thyroid) | Lowers | Low thyroid hormone reduces SHBG |
| High testosterone / anabolic steroids | Lowers | Testosterone itself suppresses SHBG |
| Fatty liver disease | Lowers | Metabolic dysfunction in the liver |
Low SHBG is the flip side of a common trap: a man with obesity or insulin resistance can have a low total testosterone but a normal free testosterone, because his low SHBG releases a bigger share of what he has. Treating him as deficient off the total number alone could be a mistake.
How Does SHBG Change the Way I Read My Labs?
This is where most people get tripped up. Your total testosterone and your free testosterone can tell two different stories, and SHBG is the translator. Here are the four scenarios that actually show up on lab reports:
| Scenario | Total T | SHBG | Free T | What it usually means |
|---|---|---|---|---|
| 1. Both normal | Normal | Normal | Normal | Likely fine. Look elsewhere for symptoms. |
| 2. Hidden low | Normal | High | Low | Classic SHBG trap. Total looks OK, but you're functionally low. |
| 3. False alarm | Low | Low | Normal | Total looks low, but free is fine. May not need treatment. |
| 4. Truly low | Low | Normal/low | Low | Genuine deficiency on both counts. |
Scenario 2 is the one that gets missed most. A man comes in tired, low libido, foggy. His total testosterone reads 450 ng/dL, smack in the normal range, so he's told he's fine. But his SHBG is sky-high, his free testosterone is rock bottom, and he's symptomatic. The total number lied. This is exactly why the Endocrine Society recommends measuring free testosterone when the total is near the lower end of normal or when SHBG is likely altered (Endocrine Society 2018).
Scenario 3 is the opposite trap. An overweight man with type 2 diabetes shows a total of 250 ng/dL, which looks deficient. But his SHBG is very low, his free testosterone is actually normal, and his symptoms may stem from his weight or blood sugar rather than a true androgen problem. Reaching for the prescription pad off the total alone could miss the real issue.
The takeaway: never read total testosterone in isolation if SHBG is abnormal or your symptoms don't match. Total plus SHBG plus free, read together, is the only way to see the real picture. If you're still figuring out whether your symptoms even point to low testosterone, our guide on whether you need TRT walks through the signs and the diagnosis process.
What Are the Normal Ranges for Total Testosterone, Free Testosterone, and SHBG?
Reference ranges vary slightly by lab and by how the test was run, which is part of the problem. For years, different labs reported wildly different "normal" ranges. A landmark 2017 study fixed this by pooling 9,054 men across four large cohort studies to create a harmonized reference range, now the basis for modern lab reporting (Travison 2017).
| Measurement | Typical reference range (adult men) | Notes |
|---|---|---|
| Total testosterone | 264–916 ng/dL (ages 19–39) | Harmonized range; older men trend lower at the bottom end |
| Free testosterone | ~5–25 pg/mL (lab-dependent) | Calculated free T is preferred over direct analog assays |
| SHBG | ~10–57 nmol/L (lab-dependent) | Wide variation; trends matter more than a single value |
| Bioavailable testosterone | ~110–575 ng/dL (lab-dependent) | Free plus albumin-bound |
A few practical points on these numbers:
- The harmonized 2.5th, 50th, and 97.5th percentiles for healthy nonobese men ages 19–39 are 264, 531, and 916 ng/dL (Travison 2017). The 531 figure is the true median, which surprises men who think 600 or 700 is "average."
- Free testosterone and SHBG ranges differ a lot between labs. Always read your result against the range printed on your own report, not a number from the internet.
- The clinical diagnostic thresholds differ from population ranges. The AUA uses a total testosterone below 300 ng/dL on two early-morning tests as its cutoff for testosterone deficiency, combined with symptoms (AUA guideline).
Converting Between ng/dL and nmol/L
Outside the US, testosterone is often reported in nmol/L. To convert total testosterone from ng/dL to nmol/L, multiply by 0.0347. So 300 ng/dL is about 10.4 nmol/L, and 264 ng/dL is about 9.2 nmol/L. To go the other way, divide by 0.0347.
How Is Free Testosterone Measured (and Why Do Some Tests Lie)?
Not all free testosterone tests are created equal. This is a genuinely important detail, because the cheapest, most common method is also the least reliable.
| Method | How it works | Reliability |
|---|---|---|
| Equilibrium dialysis | Physically separates free testosterone in the lab | Gold standard, accurate, expensive |
| Calculated free T (Vermeulen) | Math formula using total T, SHBG, and albumin | Good, widely used, recommended |
| Direct analog (immunoassay) | A single antibody-based measurement | Unreliable, often inaccurate |
The direct analog assay is the one to watch out for. It's cheap and many labs default to it, but it systematically misreads free testosterone and disagrees with the gold standard. Major guidelines steer clinicians away from it.
The practical workaround most experts recommend is calculated free testosterone, usually with the Vermeulen equation, which estimates free T from your total testosterone, SHBG, and albumin (Vermeulen 1999). The Endocrine Society endorses calculating free testosterone from total T and SHBG as an acceptable approach (Endocrine Society 2018). It correlates well with equilibrium dialysis for most men, which is exactly why you want SHBG measured alongside your total. Research continues to refine these calculations against the dialysis gold standard, especially at very high or very low SHBG (Fiers 2018).
You can plug your own numbers into a free Vermeulen calculator online. If your lab gives you total T, SHBG, and albumin, you can estimate your free testosterone yourself. That's a more trustworthy number than a direct analog result.
When Should I Get Free Testosterone and SHBG Tested?
Total testosterone is the right first test for most men. But there are specific situations where total alone isn't enough, and you should make sure SHBG and free testosterone are on the order. The Endocrine Society spells these out (Endocrine Society 2018):
- Your total testosterone is borderline. If it's hovering near the bottom of the range, free testosterone settles the question.
- You're older. SHBG rises with age, so free T can be low even with a respectable total.
- You have obesity, diabetes, or insulin resistance. These lower SHBG and can make total T look falsely low.
- You have thyroid disease. Both overactive and underactive thyroid shift SHBG.
- You have liver disease. The liver makes SHBG, so liver problems distort it.
- Your symptoms don't match your total number. The single biggest reason. When the story and the lab disagree, SHBG and free T usually explain why.
If none of these apply and your total testosterone is clearly normal with no symptoms, you may not need the full panel. But the moment your numbers are confusing, SHBG and free testosterone turn the lights on.
How Should Blood Be Drawn for an Accurate Result?
Even a perfect panel is worthless if the blood was drawn at the wrong time. Testosterone is not steady throughout the day, and a few simple rules make or break the result.
| Rule | Why it matters |
|---|---|
| Draw before 10 a.m. | Testosterone peaks in the morning and falls through the day |
| Fast beforehand | Eating, especially sugar, transiently lowers testosterone |
| Confirm with a second test | A single low reading isn't a diagnosis |
| Avoid testing when acutely ill | Illness temporarily drops testosterone |
Testosterone follows a daily rhythm, with the highest levels in the morning and a meaningful drop by afternoon (Brambilla 2009). That's why guidelines insist on early-morning draws. A "low" reading taken at 4 p.m. might be perfectly normal at 8 a.m.
Food matters too. A glucose load or a regular meal temporarily lowers testosterone in healthy men, which is why fasting morning samples are the standard (Gagliano-Jucá 2019). Grab a sugary coffee on the way to the lab and you may sabotage your own result.
And one reading is never enough. Both the Endocrine Society and the AUA require two separate morning measurements before diagnosing deficiency, because day-to-day swings are normal (AUA guideline). For the full rundown on which tests to run and how often, see our guide to TRT blood work and monitoring.
What If My Total Is Normal But I Still Have Symptoms?
This is the most common frustration, and it's almost always Scenario 2 from the table above: normal total, high SHBG, low free testosterone.
Here's the move. Ask for SHBG and a calculated free testosterone, drawn fasting in the morning. If your SHBG comes back high and your calculated free T comes back low, you've found the disconnect. Your total was never the problem. Your free fraction was.
From there, the conversation with your doctor changes. The goal isn't to chase your total number into the stratosphere. It's to address why your free testosterone is low. Sometimes that means treating an underlying cause (thyroid, a medication, weight). Sometimes, with symptoms and confirmed low free T, it means a conversation about treatment.
What you should not accept is being dismissed because "your testosterone is normal" when only the total was measured. That's an incomplete workup. If your current provider won't look past the total number, it may be time to find one who runs the full panel. Our guide on how to choose a TRT provider covers what good evaluation looks like, and you can compare TRT providers that include proper lab work on TRT Atlas.
A Worked Example: Same Total, Different Reality
Numbers make this concrete. Picture two men, both with a total testosterone of exactly 400 ng/dL.
| Man A | Man B | |
|---|---|---|
| Total testosterone | 400 ng/dL | 400 ng/dL |
| SHBG | 25 nmol/L (normal) | 70 nmol/L (high) |
| Calculated free T | ~9 ng/dL (normal) | ~5 ng/dL (low) |
| Symptoms | None | Fatigue, low libido, fog |
Same total. Completely different situations. Man A is fine. Man B has high SHBG locking up his testosterone, leaving him functionally low and symptomatic, despite an identical headline number. If a doctor only looked at total testosterone, both men would be told they're "normal," and Man B would walk out untreated and miserable.
This is the entire case for reading total, SHBG, and free testosterone together. The total is the start of the story, not the end of it.
How Does This Affect TRT Decisions and Cost?
If you and your doctor land on treatment, SHBG keeps mattering after diagnosis. Men with low SHBG often clear testosterone faster and may need different dosing rhythms than men with high SHBG. Free testosterone, not just total, helps guide how treatment is dialed in over time.
It also shapes how you read follow-up labs. On treatment, your total testosterone might look great while your free fraction tells a more nuanced story, or vice versa. The same logic applies: track SHBG and free testosterone, not total alone. To understand the full monitoring picture once on therapy, see our deep dive on TRT blood work and monitoring and our overview of TRT side effects and safety.
The lab work itself is a recurring cost, not a one-time fee, and a proper panel (total, free, SHBG, plus safety markers) costs more than a bare total. Factor that into your planning. You can estimate your real all-in cost with the TRT cost calculator, and weigh clinic options side by side on our compare page.
Frequently Asked Questions
Can I have low free testosterone with a normal total testosterone? Yes, and it's common. High SHBG locks up a larger share of your testosterone, dropping the free, usable fraction even when the total looks fine. This is exactly why guidelines recommend checking free testosterone when SHBG might be altered or when symptoms don't match the total (Endocrine Society 2018).
Is free or total testosterone more important? Free testosterone is what your cells actually use, so it often tracks symptoms better. But total testosterone is still the right first test for most men. The most reliable read comes from looking at total, SHBG, and free together, not picking one in isolation.
What is a good SHBG level? Typical lab ranges run roughly 10–57 nmol/L, but the "right" number depends on the rest of your panel. Very high SHBG can drag free testosterone down; very low SHBG often signals obesity or insulin resistance. Read your SHBG against your total and free testosterone, and against the range on your own report.
Why does my testosterone need to be tested in the morning? Testosterone peaks in the morning and falls through the day, so an afternoon draw can read falsely low (Brambilla 2009). Eating, especially sugar, also lowers it temporarily (Gagliano-Jucá 2019). Fasting, before 10 a.m., is the standard for an accurate result.
Should I trust a "free testosterone" result from a cheap lab panel? Be careful. Many cheap panels use a direct analog immunoassay, which is unreliable for free testosterone. The better approach is a calculated free testosterone using your total T, SHBG, and albumin via the Vermeulen equation (Vermeulen 1999), which the Endocrine Society accepts as a valid method (Endocrine Society 2018).
Related Guides
- Do I Need TRT? Low-Testosterone Symptoms & How It's Diagnosed
- TRT Blood Work: The Labs & Monitoring Schedule
- Estrogen Management on TRT (and the Anastrozole Debate)
- TRT Side Effects & Safety: What the Evidence Says
- How to Choose a TRT Provider: Telehealth vs In-Person
- Compare TRT providers and estimate your cost
Sources
- Travison TG, et al. Harmonized Reference Ranges for Circulating Testosterone Levels in Men of Four Cohort Studies. J Clin Endocrinol Metab. 2017. PMID 28324103
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018. PMID 29562364 — also the Endocrine Society guideline page
- Mulhall JP, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. J Urol. 2018. PMID 29601923 — also the AUA guideline page
- Vermeulen A, et al. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999. PMID 10523012
- Fiers T, et al. Reassessing Free-Testosterone Calculation by LC-MS/MS Direct Equilibrium Dialysis. J Clin Endocrinol Metab. 2018. PMID 29618085
- Brambilla DJ, et al. The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men. J Clin Endocrinol Metab. 2009. PMID 19088162
- Gagliano-Jucá T, et al. Oral glucose load and mixed meal feeding lowers testosterone levels in healthy eugonadal men. Endocrine. 2019. PMID 30191441