Testosterone levels are measured through blood tests. Most doctors agree that a “normal” reading falls anywhere between 300 to 1,000 nanograms per deciliter (ng/dL). About 40% of men over age 45 will have levels that come in below that range. But a low reading by itself isn’t enough to warrant alarm.

In fact, it’ll likely have a lot to do with the time of day doctors test your blood. The best time for testing is between 7 and 10 a.m. “Different hormones have different patterns of secretion,” says Ronald Swerdloff, MD, chief of endocrinology at Harbor UCLA Medical Center. “Normal testosterone ranges are based on morning samples, when the average person is at a higher level. Afternoon tests may give a false impression of low levels.”

Swerdloff says you should get multiple tests -- at least two over the course of a couple of weeks or months. You’ll want to make sure you have low T before you take any action.

More Than Just a Number

Even if your testosterone levels are below the recommended range, you still might not have to worry. Doctors say that a reading between 200 and 300 ng/dL is sort of a gray area.