What Is a Blood Test?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs are working and see if medical treatments are helpful.

To help your child get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is anxious about it, work together on ways to stay calm.

What Is Testosterone?

Testosterone (tess-TOSS-tuh-rone) is a hormone that plays an important role in sexual development. As puberty approaches — usually when kids are between 10 and 14 years old — the pituitary gland secretes two hormones (luteinizing hormone, or LH; and follicle-stimulating hormone, or FSH). These hormones work together to stimulate the testes to make testosterone.

Increased testosterone production leads to deeper voices, bigger muscles, and body and facial hair. It also helps the testes make sperm.

Why Are Testosterone Tests Done?

A testosterone test measures the blood level of this hormone. Doctors might order two separate assessments as part of a testosterone test:

• total testosterone: This measures all testosterone in the body, including the amount attached to proteins. Proteins help carry testosterone through the bloodstream.
• free testosterone: This measures only the testosterone that's not attached to proteins.

Human sex hormones work closely with one another. For example, low testosterone levels can happen if the pituitary gland doesn’t make enough LH or FSH to stimulate production. So doctors might do a testosterone test along with blood tests that measure LH or FSH.

Doctors also might order the test if puberty starts earlier or later than expected.

The test also can check for damage or disease of the testes, ovaries, adrenal glands, or pituitary gland, and check for steroid use.

In teens and adults, testosterone levels can help doctors evaluate fertility or menstrual problems and sexual function.

What if I Have Questions?

If you have questions about the testosterone test or what the results of the test mean, talk to your doctor.