Total testosterone, free testosterone, bioavailable testosterone – you may be confused. Which testosterone level is most important?
If you been to this website before you know that we emphasize the fact that testosterone is a total body hormone, not just a muscle or sex hormone. And, that testosterone levels decline as we age (but not necessarily because we age as a recent study suggests that the decline is lifestyle related) creating a variety of signs and symptoms in both men and women.
Men make about 7 mg of testosterone a day (range of 3 mg to 10 mg) with 95% being produced in the testes and the remaining 5% by the adrenal glands. Women also make testosterone (ovaries, adrenal glands, and conversion from other hormones), but a woman’s production is one-eighth to one-tenth that of men. But, women can suffer from low T (low testosterone), too.
Testosterone Level and Binding Proteins
Most of the testosterone we make is bound to 2 proteins; sex-hormone binding globulin (SHBG) and albumin. In fact, 98% of testosterone is bound to these 2 proteins. The remaining 2% or so is called the free testosterone. It is the free testosterone that actually enters the cell, hooks up a testosterone receptor, and then turns that cell on to do what that cell has been programmed to do when stimulated by testosterone (muscle cell will build muscle, a bone cell will build bone, etc.).
The total testosterone is just that – it’s all the testosterone floating through your blood stream and includes the free testosterone, the testosterone bound to albumin, and the testosterone bound to SHBG. It is the most common testosterone level ordered by physicians, but clinically the least useful level, yet the level upon which most treatment guidelines are based upon.
Here’s why the total testosterone may not be the best testosterone level to obtain. A man (or woman) can have a “normal” total testosterone level based on reference ranges, but he or she may have an excessive amount of testosterone bound to protein, thus having a low amount of free testosterone to enter the cell potentially developing symptoms related to low testosterone.
SHBG’s and Albumin’s Affinity to Bind Testosterone
Sex-hormone binding globulin binds to testosterone much more strongly than albumin does to testosterone. SHBG’s affinity to bind testosterone is somewhere in the magnitude of 100 to 1000 times stronger than albumin’s affinity to bind testosterone. What’s the significance of this? First, about 60% to 70% of the total testosterone is bound to SHBG and the remaining 30% to 40%% to albumin (keep in mind the 2% that is free). Testosterone can disassociate (become unbound) from albumin if needed, and therefore, is potentially bioavailable for the cells to use. Testosterone bound to SHBG is essentially “locked up” and is not available for use.
You can think of bioavailable testosterone as a reserve that the body can tap into when the free testosterone is running low. So it’s a bit like indicator coming on in your car telling you that you have so many gallons of gas left in your tank. How much bioavailable testosterone ever actually enters the cell and is used in these situations is unknown.
Bioavailable testosterone is calculated from a formula. To apply the formula you need to know your total testosterone, SHBG, and albumin levels.
Now that you understand testosterone physiology better, you’ve probably have already concluded there are 2 ways to increase your free testosterone. The most obvious is to increase total testosterone, and the other way to raise the free testosterone is by reducing the amount of testosterone bound to SHBG.
What Factors Affect Sex-Hormone Binding Globulin?
Sex-hormone binding globulin is affected by many factors. SHBG naturally increases with age. Other hormones affect SHBG and include insulin, growth hormone, testosterone, estrogen, and thyroid. Obesity and insulin resistance lowers SHBG which may sound like a good thing, but many other factors offset that and testosterone levels tend to be lower in diabetics and obese individuals. There is some evidence that SHBG can be affected by herbs and supplements. Green tea is reported to raise SHBG. Vitamin D, boron, and stinging nettle root are reported to lower it.
Our Recommendations
We get a total and free testosterone on all our patients at every lab draw in addition to other hormones and labs. At this point we believe the combination of both gives us an accurate assessment. We believe the free testosterone level is the most clinically useful level to obtain in our patients. As we learn more about SHBG and the factors that affect it that might be modifiable there may be situations in certain patients where obtaining a SHBG level could be clinically useful (ie. stop drinking so much green tea because it’s raising your SHBG and lowering your free testosterone).
Unfortunately, most physicians simply obtain a total testosterone on their patients. If your doctor does this, ask him or her politely why, and suggest that a free testosterone or bioavailable testosterone level be obtained, too.
See related articles.
“Diabetes and Low Testosterone”
“Testosterone and Cardiovascular Disease”
Hi,
I was wondering if you knew how much free floating testosterone women generally have? Thank you!
Alicia,
Free testosterone is usually 1 to 2% of the total testoterone. It is usually reported in different units, however, than the total testosterone.
Hi,
What about normal values for total testosterone and very high values for free-testosterone in woman, also having normal values for SHBG? Could be a fals elevated free-testo due tu some external factors or it is a real pathology?
We consider the optimal range for free testosterone in women to be 7-10 pg/ml.
Dr.Joe , my total testosterone is 15 ng/dl & my free testosterone is 0.8 pg/ml & bio avail is 1.7 ng/dl . I’m 49 yr old female in perimenopause & have been suffering low libido and hairloss. Could low test be the reason? Also I’m wondering if free testosterone is DHT ? Beth
Yes, low testosterone could be the cause of your low libido. DHT is not the same as free testosterone. Elevated DHT levels can contribute to hair loss. Both high and low thryoid function can also contribute to hair loss.
I am a 24 year old male. I have had signs of low t for a long time including ED low libido.
here are My latest test results.
Cortisol Leve
21.2 mcg/dL
Progesterone
0.9 ng/mL
Estrogens Total
67 pg/mL
Testoster Total
410 ng/dL
Testoster Free
80.1 pg/mL
Prolactin
7.2 ng/
What is your opinion on the levels and What other tests would you recommend I get to determine better whats wrong and what the best treatment would be .
thankyou
The biggest test that stands out is your estradiol level is too high which means you are converting too much testosterone into estradiol through an enzyme called aromastase that resides in fatty tissues primarily. So if you are overweight we can expect some improvement in your testosterone levels simply losing some weight if that is the case. Both your total and free testosterone are “normal” meaning they fall in the reference range but suboptimal for a 24 year old with symptoms. Lowering estradiol will improve both. You can consider zinc or Chrysin over the counter to lower to estradiol as they block aromatase and there are prescription medicatons like anastrozole. One test I would recommend is an LH or luteinizing hormone. It’s produced in the pituitary gland and stimulates the testes to make testosterone. If it is low then HCG or clomid could be considered to raise your testosterone levels. Direct testosterone replacement at your age is not ideal because it will make you less fertile but not uncommonly used along with HCG to keep the testes working. Also cortisol is borderline high and adds to weight gain. It’s the stress hormone so anything you can do to lower and manage stress should help the situation. Are you on any medications that can affect libido ro or testosterone – antidepressants, narcotic pain meds, cholesterol drugs, and blood pressure meds? Hope that helps.
thanks, that is the most help Ive received from anyone so far.
I apologize for not mentioning my steroid use which I have discontinued, I am currently trying to get my levels back on track and am on 20 mg nolvadex and 50mg clomid now. Im taking vitamin C, b6 and DHEA here and there to possibly help my cortisol. If I don’t see improvemet in a month or so I was going to ask my doctor about adding remeron or cytadren, thanks again for your input.
I am a 32 year old male, with a total testosterone level of 330 (flagged as low) and a free testosterone level of 10.7, just north of low. I was not expecting to need to look into TRT at my age, but is this something I should consider at those numbers?
Testosterone levels are dropping globally – probably environmental. You want to make sure there is not a pituitary reason for the relatively low testosterone levels and recommend you have a prolactin level and luteinizing hormone level checked. Treating you with testosterone is not ideal as it will make you less fertile – if that is a concern. I assume you are having symptoms and if need to be treated HCG or climid alone which will maintain fertility would be preferable to testosterone therapies.
Hi, I’m a 44 year old male 185lbs, body fat 18%, on trt for 8 weeks. I had this blood work done 2 days after my injection of 100mg weekly. Here’s my results
E2 (52)
Shbg (21)
Albumin (4.6)
Testosterone calc free (2.4%)
Total testosterone (758ng) last week (852ng)
Testosterone calc bio (48. 7%)
Testosterone calc free (18.4%)
Testosterone calc bioav (369.7)
Hi, what would be the recommended dosages for ivy & clomid?
Thanks!
25 to 50 mg of Clomid a day for males with low testosterone
Hi,
my physicians say my T is normal:
Testosterone Total 1015 ng/dL/Range: 240 – 950 ng/dL
Sex Hormone Binding Globulin 131 nmol/L/Range: 11 – 80 nmol/L
Free Testosterone Calculated 8.04 ng/dL/Range: 4.7 – 24.4 ng/dL
Yet I have ongoing gynecomastia and the assorted associated effects that seem to point to too much estrogen – yet I take no T or E supplements, do not do any drugs and am a moderate drinker (beer/wine).
Do you think the above is ‘normal’ (fungible term, I know) for a 54 yr old male, 6′ 188lbs?
Thank you.
Your free T is relatively low. Given your total T range your free T should be more in the low 20s. Your free T is low because your SHBG is too high. Alcohol consumption could be a factor in this. Have you had your estradiol (estrogen) level measured. 20-40 is the ideal range for estradiol. If above this, then an estrogen blocker like anastrozole would be helpful in lowering the estradiol level – but probably wise to cut back on alcohol consumption, too. Here’s a link to another article on the website regarding nutritional supplements than can lower estradiol and raise the free T. https://livelongstayyoung.com/nutritional-supplements-male-sexual-health/
Thank you so much; very helpful. I will check into it.
Your total t is above referance range , my testosterone level is about 135 ng/dl so you have at least 6 times more testosterone in you and im 27, i would kill to have those lab results to be honest.
I’ll trade you my total T if you’re willing to take my high SHBG and low free T — not much good if my body can’t seem to actually use it … 🙁