Low testosterone · Telehealth for men · Canada & USA
What is the difference between free and total testosterone?
Total testosterone counts all the testosterone in your blood. Free testosterone is the small part that is not bound to a protein — only 2 to 4 percent, according to the Endocrine Society. Most is held by SHBG (tightly) and albumin (loosely). When SHBG runs high or low, or your total T sits near the lower limit, free T can tell a different story. We help men in Canada and the USA read total T, SHBG, albumin and free T together by telehealth, then build a written nutrition, training and sleep plan with follow-up labs.
Part of our low testosterone and andropause guide for men in Canada and the USA.
Total, free and bioavailable testosterone
The total testosterone on your lab report is the sum of everything in circulation. According to the Endocrine Society’s 2018 guideline, most of it is bound to sex hormone-binding globulin (SHBG) and albumin, a little to cortisol-binding globulin and orosomucoid, and only 2 to 4 percent travels unbound, or free. “Bioavailable” testosterone is the free part plus the part loosely held by albumin, which lets go easily in tissues with slow blood flow such as the liver and brain. Under the free hormone hypothesis, it is the unbound hormone that gets into cells and acts. So two men with the same total T can have different amounts of usable testosterone if their SHBG differs.
SHBG and testosterone: what raises and lowers it
SHBG is the main carrier. When it runs high, more testosterone is held tightly, so total T can look normal while free T is low. When it runs low, total T can read low while free T is fine. The Endocrine Society lists what moves it. Lower SHBG: obesity, diabetes, an underactive thyroid, nephrotic syndrome, acromegaly, and glucocorticoids, some progestins and androgenic steroids. Higher SHBG: aging, cirrhosis and hepatitis, an overactive thyroid, HIV, some anticonvulsants and estrogens. Gene variants can push it either way. Age shows the pattern clearly: in follow-up data from the Massachusetts Male Aging Study (Feldman and colleagues, 2002), SHBG was about 1.6 percent higher for each year of age, while free and albumin-bound testosterone were about 2 percent lower and total T only 0.8 percent lower. Low SHBG also travels with insulin resistance: in a 2009 New England Journal of Medicine study by Ding and colleagues, low SHBG strongly predicted type 2 diabetes in women and men. More on how age and weight compare in low T from aging or from weight.
Age
SHBG climbs with age, so free T falls faster than total T in older men.
Weight and blood sugar
Obesity, insulin resistance and diabetes go with lower SHBG, which can pull total T down.
Thyroid and liver
An overactive thyroid or liver disease raises SHBG; an underactive thyroid lowers it.
Medications
Glucocorticoids and androgenic steroids lower SHBG; some anticonvulsants and estrogens raise it.
Calculated free testosterone: total T, SHBG and albumin
Most free T results are calculated, not measured. The Endocrine Society says free T should be measured by equilibrium dialysis or estimated with a formula that uses total testosterone, SHBG and albumin and accurately reflects dialysis. The best-known formula comes from Vermeulen, Verdonck and Kaufman (Journal of Clinical Endocrinology & Metabolism, 1999). They tested it on samples with SHBG ranging from very low to extremely high, and calculated free T was almost identical to dialysis in every condition studied except pregnancy. A calculation is only as good as its inputs, so it needs an accurate total T (the guideline favours CDC-certified assays, and mass spectrometry offers higher precision at low levels), plus SHBG and albumin from the same sample.
Dialysis, calculated or a direct analog test?
Equilibrium dialysis is the reference method: serum sits against a membrane that only unbound testosterone can cross. It is accurate but slow, so it is usually sent to a reference lab. Direct analog immunoassays are the quick free T tests many local labs offer. In Vermeulen’s study their values were only a fraction of the dialysis result, and that fraction shifted with SHBG, so the error is biggest exactly when free T matters most. The Endocrine Society says these direct analog tests are inaccurate and should not be used, and advises a reliable reference lab for free T. The same study found the free androgen index (testosterone divided by SHBG) also varied with SHBG and was not a reliable index. Look for the method name on your report: “calculated” or “equilibrium dialysis” is what you want to see.
Units: nmol/L vs ng/dL, pmol/L vs pg/mL
The Canadian Urological Association guideline writes total T in nmol/L; the Endocrine Society and American Urological Association write it in ng/dL. Testosterone weighs 288.4 grams per mole (PubChem), so 1 nmol/L is about 28.8 ng/dL, and for free T 1 pg/mL is about 3.47 pmol/L. The Endocrine Society’s own pairs line up: 264 ng/dL is 9.2 nmol/L, 320 ng/dL is 11 nmol/L, and a free T of 64 pg/mL is 220 pmol/L. To compare, multiply nmol/L by 28.8 to get ng/dL, and multiply free T in pg/mL by 3.47 to get pmol/L. Free T also sits in a far smaller unit than total T (a picomole is a thousandth of a nanomole), so a free T of 300 is not “higher” than a total T of 15. Always read the unit next to the number, or convert it in our testosterone calculator.
Total T
nmol/L × 28.8 = ng/dL. ng/dL ÷ 28.8 = nmol/L.
Free T
pg/mL × 3.47 = pmol/L. pmol/L ÷ 3.47 = pg/mL.
Results from both countries
We line up results from Canadian and US labs in one unit so the trend is clear.
What is a normal free testosterone for men?
There is no single agreed number. The Endocrine Society says a harmonized free T range has not been established, so ranges vary with the dialysis method or formula, and labs set their own lower limits. Total T now has one: 264 to 916 ng/dL (9.2 to 31.8 nmol/L) in healthy, non-obese men aged 19 to 39, for CDC-certified assays. The free T figure researchers use most comes from the European Male Ageing Study (Wu and colleagues, New England Journal of Medicine, 2010; 3,369 men aged 40 to 79). It defined late-onset hypogonadism as at least three sexual symptoms (poor morning erections, low sexual desire, erectile dysfunction) with total T below 11 nmol/L and free T below 220 pmol/L (64 pg/mL). In a later analysis of the same men, calculated free T averaged 326 pmol/L in those with normal total and free T. The Canadian Urological Association treats total T below 10 nmol/L as a reasonable threshold, and the American Urological Association uses below 300 ng/dL on two early-morning tests with symptoms. We read the range on your own report, the method behind it and your symptoms together.
Total testosterone normal but you still have symptoms?
This is where free T earns its place. In a 2016 European Male Ageing Study analysis (Antonio and colleagues, Journal of Clinical Endocrinology & Metabolism; 3,334 men aged 40 to 79), 277 men had a normal total T but a low calculated free T. They were older and in poorer health, had higher SHBG and LH, and reported more sexual and physical symptoms, with lower hemoglobin and bone scores. The 96 men with low total T but normal free T were younger and heavier, with lower SHBG, and lacked the features of low testosterone. The authors concluded that low free T, even with a normal total, goes with symptoms. The Canadian Urological Association adds two points: look-alike conditions such as depression, an underactive thyroid and sleep disorders should be ruled out, and high SHBG can effectively neutralize circulating testosterone, so in unclear cases SHBG with a calculated free or bioavailable T adds insight. See the full picture in low testosterone symptoms and how rest fits in low testosterone and sleep.
High SHBG can hide it
A normal total with high SHBG can still leave free T low, often in older men.
Low SHBG can mislead
Heavier men can show a low total with normal free T and few symptoms.
Rule out look-alikes
Low mood, thyroid problems and poor sleep cause many of the same symptoms.
Read them together
Total T, SHBG, free T and LH side by side, alongside how you actually feel.
When free testosterone is worth checking
Start with the basics: a fasting, early-morning total T, repeated on another morning, because the Endocrine Society notes that 30 percent of men with one low result are normal on the repeat. The guideline then recommends free T in two situations: when total T sits near the lower limit (for example 200 to 400 ng/dL), and when a condition that changes SHBG is present. When total T is far below the limit (for example under 150 ng/dL), free T is unlikely to be normal, so it is generally not needed. Symptoms with a normal total T are a third reason, as the European Male Ageing Study data above show. See low testosterone labs to ask for and when to get checked for low T.
How Odin helps
Odin Health Labs is telehealth for men in Canada and the USA with andropause and low testosterone symptoms. On a free call we go through your symptoms, weight, sleep, medications and the labs you already have. We read your total T, SHBG, albumin and free T with you in plain language, check whether free T was calculated, measured by dialysis or run on a direct analog test, put results from Canadian and US labs into the same units, and look for what might be moving your SHBG. Then we build a written plan for nutrition, training, sleep and stress, with follow-up check-ins and repeat labs so you can see what is changing. Our health coaching keeps the plan on track, functional health looks at the whole picture, and our supplements page shows where they fit.
Telehealth consults
Video or phone, anywhere in Canada or the USA, at a time that fits your week.
SHBG and free T review
Total T, SHBG, albumin and free T read together, with the method and units checked.
A written plan
Nutrition, training, sleep and stress steps aimed at what is moving your numbers.
Follow-up and repeat labs
Check-ins and repeat labs from the same method, so changes are real, not lab noise.
From confusing numbers to a plan
Here is how we work with you, start to finish.
- Step 1
Talk through symptoms
On a free call we go through your energy, drive, mood, sleep, weight, training and medications.
- Step 2
Get the right labs
Two fasting early-morning total T results, plus SHBG, albumin and a calculated free T when they help.
- Step 3
Read the numbers together
Method, units and SHBG checked, then a written nutrition, training, sleep and stress plan.
- Step 4
Track and adjust
Regular check-ins and repeat labs show what is shifting, and we adjust the plan with you.
Sources
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2018;103(5):1715–1744. doi.org/10.1210/jc.2018-00229
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab 1999;84(10):3666–3672. doi.org/10.1210/jcem.84.10.6079
- Wu FC, Tajar A, Beynon JM, et al. Identification of late-onset hypogonadism in middle-aged and elderly men. N Engl J Med 2010;363(2):123–135. doi.org/10.1056/NEJMoa0911101
- Antonio L, Wu FC, O’Neill TW, et al. Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. J Clin Endocrinol Metab 2016;101(7):2647–2657. doi.org/10.1210/jc.2015-4106
- Feldman HA, Longcope C, Derby CA, et al. Age trends in the level of serum testosterone and other hormones in middle-aged men: longitudinal results from the Massachusetts Male Aging Study. J Clin Endocrinol Metab 2002;87(2):589–598. doi.org/10.1210/jcem.87.2.8201
- Ding EL, Song Y, Manson JE, et al. Sex hormone-binding globulin and risk of type 2 diabetes in women and men. N Engl J Med 2009;361(12):1152–1163. doi.org/10.1056/NEJMoa0804381
- Grober ED, Krakowsky Y, Khera M, et al. Canadian Urological Association guideline on testosterone deficiency in men: Evidence-based Q&A. Can Urol Assoc J 2021;15(5):E234–E243. doi.org/10.5489/cuaj.7252
- Mulhall JP, Trost LW, Brannigan RE, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline (2018). American Urological Association. auanet.org testosterone deficiency guideline
- National Library of Medicine. PubChem compound summary: testosterone (CID 6013), molecular weight 288.4 g/mol. pubchem.ncbi.nlm.nih.gov
Frequently asked questions
What is the difference between free and total testosterone?
Total testosterone is all the testosterone in your blood: the part held tightly by SHBG, the part held loosely by albumin, and a small unbound part. Free testosterone is that unbound part, only 2 to 4 percent of the total according to the Endocrine Society (2018). Free plus albumin-bound testosterone is called bioavailable testosterone. Total T is still the first test. Free T helps when SHBG is unusual or total T sits near the lower limit. We read both with you and explain what they mean for your symptoms.
What is a normal free testosterone level for men?
Each lab sets its own range, because the Endocrine Society notes that no harmonized free T range exists yet and results depend on the method used. The cut-off researchers use most comes from the European Male Ageing Study (NEJM, 2010): free T below 220 pmol/L (64 pg/mL), with total T below 11 nmol/L and at least three sexual symptoms, defined late-onset hypogonadism. Men in that study with normal total and free T averaged 326 pmol/L. Check the unit and the method printed on your report before you compare numbers.
What is SHBG and why does it matter?
Sex hormone-binding globulin is the protein that holds most of your testosterone tightly. High SHBG, which comes with aging, liver disease, an overactive thyroid and some anticonvulsants, can make total T look normal while free T is low. Low SHBG, which comes with obesity, diabetes and an underactive thyroid, can make total T look low while free T is normal. In the Massachusetts Male Aging Study, SHBG was about 1.6 percent higher for each year of age. We look at what may be moving your SHBG and build the weight, nutrition, training and sleep plan around it.
My total testosterone is normal but I have low-T symptoms. What should I check?
Ask for SHBG and a calculated free testosterone from the same fasting, early-morning sample. In a 2016 European Male Ageing Study analysis, men with normal total T but low calculated free T had higher SHBG and more sexual and physical symptoms. The Canadian Urological Association (2021) also points to look-alike conditions such as depression, an underactive thyroid and sleep disorders. We go through your symptoms and labs together and plan the next tests and lifestyle steps with you.
Which free testosterone test is most accurate?
Equilibrium dialysis is the reference method. A free T calculated from total T, SHBG and albumin was almost identical to dialysis in a 1999 study by Vermeulen and colleagues. Direct analog immunoassays gave values that were only a fraction of the dialysis result, and the Endocrine Society says they are inaccurate and should not be used. If your report says direct or analog, ask for a calculated free T or a dialysis test from a reference lab.
How does Odin Health Labs work with my doctor?
Odin Health Labs is a telehealth service for men in Canada and the USA with low testosterone (andropause) symptoms. We work alongside your own doctor: we go through your symptoms and lab results with you, including total T, SHBG, albumin and free T, help you prepare questions such as which free T method to ask for, build your nutrition, training, sleep and stress plan, and track your progress with follow-up check-ins and repeat labs. We can share your plan and results with your doctor if you choose. See our low testosterone overview and our Privacy Policy.
Want your total T, SHBG and free T read together?
A free call is the first step: we go through your symptoms and results, plan the right labs and set up nutrition, training, sleep and stress steps with you.