A testosterone level test measures the amount of testosterone in the blood and is reported as nanograms per deciliter (ng/dL). It’s also known as a serum testosterone test.

Testosterone is an androgen, or a sex hormone, produced by both males and females. It plays a role in puberty and fertility. It also affects sexual desire.

In males, the testes produce most of the testosterone. In females, the production of testosterone occurs mostly in the ovaries. Males have higher levels of testosterone than females. Doctors believe that testosterone has a significant influence on the development of many traits, including:

  • increased muscle bulk
  • higher bone mass
  • physical strength
  • body hair

However, the hormone plays an important role in women as well, including their reproductive health and the ability to feel sexual arousal.

Your doctor may order this test for a variety of reasons.

Testosterone in Males

One common reason to order this test is either early or delayed puberty. The test may also be necessary if your doctor suspects you may have low hormone levels. A low levels of testosterone in a male is also known as hypogonadism.

The symptoms of hypogonadism in a male include:

  • decreased body hair
  • decreased muscle mass
  • a low sex drive
  • erectile dysfunction
  • the growth of breast tissue, or gynecomastia

Some other possible causes of having low testosterone include:

  • delayed puberty
  • testicular damage, which can be caused by trauma, alcoholism, or the mumps
  • a hypothalamic disease
  • a pituitary disease
  • a noncancerous pituitary tumor

A number of genetic diseases can also affect testosterone levels, including Klinefelter’s syndrome, Kallmann’s syndrome, and myotonic dystrophy.

It’s also possible for a male to have too much testosterone. High testosterone levels can be problematic. Too much of this hormone can be the result of:

  • early, or precocious, puberty
  • hyperthyroidism, or overactive thyroid
  • anabolic steroids
  • congenital adrenal hyperplasia
  • androgen insensitivity syndrome
  • testicular tumor
  • adrenal tumor

Testosterone in Females

Your doctor will usually order testosterone level tests if you’re a female and they suspect you have a high level of this hormone. Too much testosterone in a female can lead to:

  • irregular or absent menstrual periods
  • infertility
  • the development of facial and body hair
  • a deepened voice

There are several reasons a female may have too much testosterone, including:

  • polycystic ovarian syndrome
  • congenital adrenocortical hyperplasia
  • ovarian cancer or tumor
  • adrenal tumor

Certain drugs can affect your testosterone levels and change the results of a testosterone level test. It’s important to tell your doctor about all medications you’re taking, including over-the-counter and prescription drugs. Your doctor may ask you to stop certain drugs before your test.

Medications that may affect this test include:

  • androgen therapy
  • steroids
  • anticonvulsants
  • barbiturates
  • clomiphene
  • estrogen therapy

Your doctor may specify a time of day for your test. Because hormone levels are highest in the morning, you may need to take this test between 7 a.m. and 10 a.m.

Your doctor may also ask you to have repeat testing, which can track hormone changes throughout the day.

A testosterone test requires taking a blood sample. This involves the following steps:

  1. A healthcare provider will clean the area where they will draw your blood. This is usually from a vein on the inside of the elbow or the back of the hand.
  2. They’ll tie an elastic band around your upper arm to make blood pool in the vein.
  3. They’ll insert a sterile needle into your vein
  4. Then, they’ll draw your blood into a tube.
  5. After collecting the blood, they’ll remove the elastic band and needle from your arm.
  6. They’ll apply pressure to the insertion site to stop bleeding and prevent bruising
  7. They’ll apply a bandage.

Having your blood taken may cause some pain or discomfort. It may feel like a pricking or burning sensation. Relaxing your arm can help ease the pain. You may continue to feel some throbbing after they remove the needle, but this should go away quickly.

Your doctor will send your blood sample to a laboratory for testing.

The risks of a blood test include:

  • multiple puncture wounds from trouble finding a vein
  • excessive bleeding
  • lightheadedness
  • fainting
  • a hematoma, which is a collection of blood under the skin
  • an infection

When your doctor receives your test results, they’ll look them over. If your testosterone level is higher or lower than normal, they’ll try to determine any underlying medical conditions based on your results.

Your doctor will discuss your results with you and help you understand what they mean. Any follow-up testing or treatment plans should be discussed during an appointment with your doctor.