What is a nocturnal penile tumescence study?

Dr. Marc B. Garnick, MD
Hematologist & Oncologist
A nocturnal penile tumescence test is used to help diagnose erectile dysfunction (ED). It monitors erections while you sleep. During the test, a recording unit collects data on the number and duration of nocturnal erections, the change in the circumference of the penis, and penile rigidity. The measurements are made by two loops: one at the base of the penis and the other at the tip. Rigidity above 70% constitutes a nonbuckling erection; below 40% represents a flaccid penis. During eight hours of sleep, three to six erections lasting 10 to 15 minutes each, on average, is considered normal, though definitions of "normal" vary.
Dr. Mehmet Oz, MD
Cardiologist (Heart Specialist)
A nocturnal penile tumescence (NPT) study or test is a simple way to determine whether you have erections at night when you are sleeping. If you do, there's a good chance that your erectile dysfunction (ED) is not caused by an organic disease such as heart disease. That's a good thing. It means that you and your doctor may want to look at other possible causes, including depression, stress, anxiety, or relationship problems. Because ED affects both a man and his sexual partner, couples therapy is often part of the solution.
Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

Men typically have three to five erections while sleeping. The Nocturnal penile tumescence (NPT) study is a test to determine whether these erections are occurring.

If you do not have erections while you sleep, the doctor will look for a health condition or medications that decrease blood flow to the penis or interferes with nerve signals that enable arousal and erection. If you experience erections in your sleep or upon awakening, your erectile dysfunction may be caused by stress or depression.

The NPT test is done two ways: the strain gauge method and the snap gauge method. The strain gauge method documents changes in circumference when elastic bands on the base and tip of the penis stretch during an erection. The snap gauge method measures erectile function with pressure-sensitive bands that break when an erection occurs.

Whatever the cause of your ED, your doctor can recommend treatment that will help.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.