This page helps you to understand blood test results for testosterone and gives you the reference range to determine if your lab test results mean that you have high, low or normal testosterone levels.
We outline the risk factors associated with both raised and lower testosterone levels.
Reference Ranges for Testosterone in men (Sign up to see ranges for Free Testosterone & female ranges):
|US Conventional Units||ng/dl||240-1200||<240 OR > 1200|
|Standard International Units||nmol/L||8.3-41.6||<8.3 OR > 41.6|
What is Testosterone
Testosterone is the main sex hormone (androgen) in men. It is responsible for male physical characteristics. Although it is considered to be a “male” sex hormone, it is present in the blood of both men and women.
Testosterone is mainly produced by special endocrine tissue (the Leydig cells) in the male testicles. It is also produced by the adrenal glands in both males and females and, in small amounts, by the ovaries in females .
Testosterone levels are diurnal, peaking in the early morning hours (about 4:00 to 8:00 am), with the lowest levels in the evening (about 4:00 to 8:00 pm). Levels also increase after exercise, particularly intense exercise .
Free Testosterone – About 45-65% of testosterone circulates in the blood bound to sex-hormone binding globulin (SHBG), and about 30% is bound to albumin. A small percentage (less than 4%) circulates as free testosterone. The free plus the albumin-bound testosterone is the bioavailable fraction, which can act on target tissues.
In many cases, measurement of total testosterone provides a healthcare practitioner with adequate information. However, in certain cases, for example when the level of SHBG is abnormal, a test for free or bioavailable testosterone may be performed as it may more accurately reflect the presence of a medical condition .
Function of Testosterone
In males, testosterone stimulates development of secondary sex characteristics, including enlargement of the penis, growth of body hair, muscle development, and a deepening voice. It is present in large amounts in males during puberty and in adult males to regulate the sex drive and maintain muscle mass. In females, testosterone is converted to estradiol, the main sex hormone in females .
Risk factors associated with Testosterone
In adult males, low testosterone may alter certain masculine physical characteristics and impair normal reproductive function. Signs and symptoms may include:
- Erectile dysfunction
- Decrease in beard and body hair growth
- Decrease in muscle mass
- Development of breast tissue (gynecomastia)
- Loss of bone mass (osteoporosis) 
Low testosterone can also cause mental and emotional changes. As testosterone decreases, some men may experience symptoms similar to those of menopause in women. These may include:
- Decreased sex drive
- Difficulty concentrating
- Hot flashes 
In females, testosterone testing may be done when a woman has irregular or no menstrual periods (amenorrhea) or is having difficulty getting pregnant, Testosterone levels can rise because conditions such as polycystic ovarian syndrome (PCOS) .
Thyroid problems, depression, excessive alcohol use and conditions such as obstructive sleep apnea can all affect testosterone levels in men and women.
Notable variations by demographic group
Testosterone is significantly higher in males than females.
Older men tend to have lower testosterone levels than younger men. Testosterone levels gradually decline throughout adulthood — about 1 percent a year after age 30 on average.
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Diet to improve Testosterone
Eliminate excess calories – Being overweight or obese can impact levels of testosterone. Eliminating excess calories to lose the extra weight can help bring testosterone back up. Likewise, for men who are underweight, getting your weight up to a healthy level can also have a positive effect on the hormone .
Eggs – Egg yolks are high in cholesterol which is a precursor to testosterone. There have been several studies that have shown eggs not to be linked to higher cholesterol, but it is advisable to monitor your cholesterol if you are going to increase your intake, particularly if you are prone to high cholesterol.
Good Fats – A study in the Journal of Clinical Endocrinology & Metabolism, showed that men who ate more ‘good fats’ for two weeks had less of a hormone that binds to testosterone, called sex-hormone-binding globulin. As a result, they had higher levels of free testosterone—the only form of testosterone that is ready to work on your tissue. Sources of good fats include nuts, avocados, eggs, fish oils, olive oil etc.
Limit Soy and Alcohol – both are linked to lower testosterone levels
Supplements for Testosterone
The use of supplements to raise testosterone is widely reported but to date there is little evidence to support the effectiveness of these products. Two supplements which have had some positive results are:
Vitamin D – In a study from Medical University of Graz, Austria, male subjects took either 3,332 IU of vitamin D per day per one year or a placebo. Free testosterone levels increased significantly in the vitamin D supplemented group, but there was no change in the placebo group. (The Institute of Medicine recommends 4,000 IU as the upper level of vitamin D intake.)
Phosphatidylserine – Supplementation with 600 mg per day for 10 days was shown to significantly increase the testosterone to cortisol ratio by both increasing testosterone and lowering cortisol. The effectiveness of long term use requires further research .
Exercise to improve Testosterone
Testosterone adapts to your body’s needs. If you are too sedentary your brain gets the message that you don’t need as much to bolster your muscles and bones. But when you are physically active, your brain sends out the signal for more of the hormone.
If you’re getting little exercise now, experts suggest:
- Build into aerobic exercise slowly starting with brisk walks
- High Intensity interval training has been linked to higher levels of testosterone
- Strength training is also proven to increase testosterone levels
- Don’t overdo it as extreme amounts of endurance exercise can lower your testosterone .
Sleep for Testosterone
George Yu MD, a urology professor at the George Washington University Medical Center in Washington, D.C., says that, for many men with low testosterone, poor sleep is the most important factor. A lack of sleep affects a variety of hormones and chemicals in your body. This, in turn, can have a harmful impact on your testosterone.
He recommends making sleep a priority, aiming for 7 to 8 hours per night, even if it means rearranging your schedule or dropping your habit of late-night TV .
If you’re under constant stress, your body will churn out a steady stream of the stress hormone cortisol. When it does, it will be less able to create testosterone. Therefore, controlling your stress is important for keeping up your testosterone .