This is challenging question because men’s testosterone levels can vary depending on a man’s age, the time of day, and even the lab processing a blood sample.
In general, a total testosterone range of 300 to 1,000 ng/dL is considered normal, according to the Endocrine Society. The American Urological Association also uses 300 ng/dL as its cutoff point for diagnosing low testosterone (hypogonadism).
Testosterone is measured with a simple blood test. Sometimes, several tests are needed for verification.
Click through this slideshow to learn more about factors that influence testosterone measurement.
Note that in the previous slide, we used the term total testosterone.
Testosterone is classified as either bound or free. About 98% of a man’s testosterone is considered bound. It is attached to proteins – albumin and sex hormone binding globulin (SHBG). These proteins help transport testosterone around the body.
The rest of a man’s testosterone is free. It is not attached to any other substances.
To get a complete picture, doctors usually consider both free and bound testosterone levels to determine a total testosterone level, which is widely used when diagnosing low testosterone.
Some factors that can affect testosterone measurement include the following:
- Age. A man’s testosterone levels naturally decline as he gets older – about 1% each year after age 40.
- Time of day. Testosterone levels are usually highest in the morning, drop as the day goes on, and are replenished during sleep. Doctors often measure testosterone between 7 a.m. and 10 a.m. to maintain consistency, especially if they are taking many measurements across time for comparison. Testing in the morning may not be as critical for older men. Research suggests that fluctuations are less evident in men over age 45 and that testing any time before 2 p.m. is acceptable.
- Labs. Measurement procedures vary from lab to lab, and some methods are more accurate than others. The type of equipment used and environmental conditions during processing and storage can also influence results.
When doctors suspect low testosterone, they look at many factors, not just blood test results. They consider the man’s overall health, age, weight, medications, and health conditions that can affect testosterone, such as diabetes and thyroid disorders. Symptoms, such as low sex drive, weakness, moodiness, and loss of muscle mass, are important as well.
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