When it comes to understanding testosterone levels, traditional testing reports one number: total testosterone. But there's more to the story, especially for men who may be experiencing symptoms of low testosterone.
Dr. Nathan Starke, a Houston urologist with fellowship training in andrology, has published research showing how free testosterone, a less commonly discussed metric, can open the door for treatments that standard testing might miss.
"With traditional testing for total testosterone, you were only low if you were below 300, depending on the guideline," Dr. Starke says. "If one patient was 299, he'd be low. If another were 301, he'd be normal. And none of that ever made any sense to me because the two men could have the exact same symptoms."
This one-size-fits-all approach left many men without answers and without treatment. Here's what Nathan Starke thinks you need to know about the difference between free and total testosterone, and why it matters for your health.
What Is Testosterone?
Testosterone is the primary male sex hormone, playing a crucial role in everything from muscle mass and bone density to mood, energy levels, and sexual function. Produced mainly in the testicles, testosterone affects nearly every system in your body.
As men age, testosterone levels naturally decline, typically about 1% per year after age 40. But some men experience more significant drops that can impact their quality of life, leading to symptoms like:
- Persistent fatigue and low energy
- Decreased muscle mass and strength
- Reduced libido and sexual function
- Mood changes, including irritability or depression
- Difficulty concentrating
- Increased body fat
Understanding your testosterone levels is the first step in addressing these symptoms. But which type of testosterone should you be measuring?
Free vs. Total Testosterone: What's the Difference?
Total Testosterone
Levels of total testosterone (most-commonly tested) reflect the sum of all three types of testosterone in your bloodstream at the time of testing:
- Testosterone bound to Sex Hormone Binding Globulin (SHBG): About 60–70% of your total testosterone is tightly bound to this protein, which makes it unable to activate androgen receptors in the cell.
- Testosterone bound to albumin: About 30–40% is loosely bound to albumin and can be released to bind with cells and initiate androgenic gene expressions
- Free testosterone: 1–3% circulates completely unbound and is also available for androgen receptor activation
SHBG plays an important role in regulating healthy hormone function, but it isn't usually manipulable in such a way as to affect the negative health effects associated with low testosterone. It accounts for an outsized share of your total testosterone levels, which can make it a misleading metric in some cases.
Free Testosterone
Free testosterone (usually must be requested from your doctor specifically) is the unbound form that's immediately available to enter your cells and do its work. It's like having money in your wallet versus money in a locked savings account. Both count toward your total wealth, but only one is readily accessible.
The functional difference between free testosterone and total testosterone sparked an observation in Dr. Starke's practice: men with normal total testosterone levels were still presenting with symptoms of low testosterone. His observation later formed the hypothesis for his research on free testosterone testing as a success indicator for hormone therapy.
"We wondered whether a newer but less well-tested version of the test called free testosterone, which may be more accurate, could help," Dr. Starke notes. "It's the circulating version of testosterone that actually does something."
Is It Better to Test for Free Testosterone or Total Testosterone?
The answer: neither is inherently better than the other. Free testosterone and total testosterone can both reveal necessary information about a man's health. Weighing the strengths and limitations of each test alongside patients' reported symptoms can provide more personalized care on a case-by-case basis.
Dr. Starke's research directly addressed this by studying 86 men experiencing clear symptoms of low testosterone (fatigue, low libido, reduced vitality) whose total testosterone levels fell within the "normal" range of 300–660 ng/dL. All of these men had low free testosterone (below 7.9 pg/mL), yet according to standard medical guidelines, they wouldn't qualify for testosterone therapy.
Dr. Starke and his colleagues continued with hormone therapy, using their low free testosterone as the indicator rather than dismissing their symptoms based solely on total testosterone numbers.
The results were striking. After six months of testosterone therapy, nearly 90% of patients reported substantial improvement in their energy and libido, with another 8% experiencing mild but noticeable improvement. Only 2% saw no benefit at all.
"We essentially proved that a huge number of men with technically normal total testosterone, but low free testosterone and appropriate symptoms, benefit symptomatically from treatment," Starke says.
How Can I Increase Free Testosterone Levels?
Before considering testosterone replacement therapy, there are several natural approaches that may help optimize your free testosterone:
Lifestyle Modifications
- Lose excess weight: Obesity increases aromatase enzyme activity, which converts testosterone to estrogen, and can lower testosterone production.
- Exercise regularly: Resistance training and high-intensity interval training have been shown to boost testosterone levels.
- Get adequate sleep: Testosterone production peaks during sleep. Dr. Starke emphasizes this connection: "As part of your natural circadian rhythm, testosterone levels rise while you sleep and spike first thing in the morning when you wake up. If you don't get the proper amount of sleep, your natural sleep cycle gets disrupted, which could lead to fewer spikes and lower average testosterone."
- Manage stress: Chronic stress elevates cortisol, which can suppress testosterone production.
- Optimize your diet: Focus on adequate protein, healthy fats, and micronutrients like zinc and vitamin D.
Medical Interventions
If lifestyle changes don't improve your symptoms, medical options include:
- Treating underlying conditions: Addressing diabetes, thyroid problems, or sleep apnea can improve hormone balance
- Medication review: Some drugs affect testosterone levels; alternatives may be available
- Testosterone replacement therapy (TRT): Available in various forms (injections, gels, patches) when other approaches aren't sufficient
What Can Total Testosterone & Free Testosterone Tell You About Your Health?
Next time you get your testosterone checked, make sure you're looking at the full picture.
Total testosterone is a valuable screening tool for tracking changes over time. But free testosterone provides crucial additional information, especially if:
- Your total testosterone is in the "borderline" or low-normal range
- You have symptoms of low testosterone despite "normal" total levels
- You have conditions that affect SHBG (obesity, diabetes, thyroid disorders)
- You're considering or monitoring testosterone replacement therapy
"Doctors, especially urologists, mostly want cut-and-dry rules to follow in the office and make things quick and efficient," Dr. Starke observes. This is why a comprehensive approach that looks at symptoms, total testosterone, free testosterone, and overall health is essential.
If you're experiencing symptoms of low testosterone, don't let a single "normal" test result be the end of the conversation. Ask your doctor about testing both total and free testosterone. The difference between the two might be the difference between living with symptoms and reclaiming your vitality.
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