From the Guidelines
Normal free testosterone levels in males typically range from 5 to 21 ng/dL (0.17-0.73 nmol/L). These levels are highest in the morning and tend to decrease with age, with men experiencing a gradual decline of about 1-2% per year after age 30 1. Free testosterone represents only about 2-3% of total testosterone in the bloodstream but is the biologically active form that can enter cells and bind to androgen receptors. The majority of testosterone in the body is bound to proteins like sex hormone-binding globulin (SHBG) and albumin.
Key Points to Consider
- Low free testosterone levels may cause symptoms such as decreased libido, erectile dysfunction, fatigue, reduced muscle mass, increased body fat, and mood changes.
- If you suspect low testosterone, it's essential to have blood tests performed in the morning when levels are highest, and testing should be repeated to confirm results before any treatment decisions are made.
- Various factors, including obesity, certain medications, alcohol use, and chronic illnesses, can affect testosterone levels.
- In patients with obesity, treatment with testosterone-replacement therapy should be considered when the morning free testosterone by equilibrium dialysis is frankly low on at least 2 separate assessments, and the hypogonadism workup has been completed to rule out an etiology of hypogonadism unrelated to obesity 1.
Important Considerations for Testing and Treatment
- The measurement of morning serum free testosterone is essential when evaluating low total testosterone clinically in a man with obesity.
- Testosterone replacement in men with obesity and hypogonadism has demonstrated favorable results, including weight loss and improvements in metabolic and body composition parameters 1.
- The method of testosterone replacement should be individualized for each patient, with transdermal testosterone preparations suggested for most hypogonadal men due to their convenience and ability to produce normal serum testosterone concentrations 1.
From the Research
Normal Free Testosterone Levels in Males
- The normal range for free testosterone in adult men is between 66-309 pg/ml (229-1072 pmol/L) as measured using a standardized equilibrium dialysis method 2.
- In younger men (19-39 years), the normal range for free testosterone is between 120-368 pg/ml (415-1274 pmol/L) 2.
- Free testosterone levels are known to decline with age, and are also negatively associated with body mass index, age, and sex hormone-binding globulin (SHBG) levels 2.
- The measurement of free testosterone is important in the diagnosis of androgen disorders, such as hypogonadism in men and androgen excess in women 3.
- Accurate measurement of total and free testosterone levels is essential for making the diagnosis of androgen disorders, and should be measured in a fasting state in the morning using a reliable assay, such as liquid chromatography tandem mass spectrometry 4.
Factors Affecting Free Testosterone Levels
- Free testosterone levels can be affected by various factors, including age, body mass index, and SHBG levels 2.
- Alterations in binding protein concentrations can also affect free testosterone levels, and measurement of free testosterone may be necessary in men with suspected alterations in binding protein concentrations 4.
- Total testosterone levels should ideally be measured in a fasting state in the morning using a reliable assay, and free testosterone levels should be measured in men with total testosterone levels only slightly above or slightly below the lower limit of the normal male range for testosterone 4.