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Tests for Erection Problems

Test Overview

Tests for erection problems can help find a cause for a man's problem in having or maintaining an erection (erectile dysfunction, or impotence). Erectile dysfunction is a common male problem. Most erection problems are caused by a combination of blood vessel, nerve, or psychological issues.

To find the cause of erection problems, your doctor will first ask about your sexual history and do a physical exam. During the physical exam, the doctor will:

Other tests that may be done as part of a physical exam include:

If the results of your physical exam and other tests are normal, your doctor may have you try a medicine, such as sildenafil (for example, Viagra), tadalafil (for example, Cialis), or vardenafil (for example, Levitra), before doing more tests.

This topic focuses on three more tests you may have after the physical exam and lab tests listed above. These three specific tests used to find the cause of erection problems are:

  • Nocturnal penile tumescence (NPT) test.
  • Intracavernosal injection test.
  • Doppler ultrasound.

Nocturnal penile tumescence (NPT) test

The NPT test checks whether a man is having normal erections during sleep. Most men have 3 to 5 full erections during deep (rapid eye movement, or REM) sleep. Men who do not have erections because of psychological problems can still have erections during deep sleep. Occasionally, some sleep problems or serious depression can prevent these normal nighttime (nocturnal) erections.

This test can be done at home or in a special sleep lab. One of two ways may be used.

  • A simple ringlike device called a snap gauge made up of plastic films is fitted around the penis. The films break at certain pressures. So an erection during sleep will cause the film to snap.
  • An electronic monitoring device records how many, how long, and how rigid the erections are during sleep. An electronic monitoring device is more expensive than using the snap gauge, but it is more accurate and gives more detailed information about erections during sleep.

Tests are usually done for at least two nights in a row. If good erections occur during sleep, the cause of the erection problems probably is not physical.

The NPT test may also be called the stamp test or the rigidity test.

Intracavernosal injection test

During this test, the doctor injects a medicine (usually alprostadil) into the side of the penis to make an erection. This is called an intracavernosal injection. A similar medicine may also be placed into the urethraClick here to see an illustration., the tube through which urine leaves the penis. This is called an intraurethral injection. The fullness of the erection and how long the erection lasts are measured.

Doppler ultrasound test

Doppler ultrasound (also called color duplex Doppler) uses a handheld tool passed lightly over the penis. The tool uses reflected sound waves to estimate the speed and direction of blood as it flows through a blood vessel. The sound waves go to a computer that changes the sounds to colors that are overlaid on a picture of the blood vessel. This shows the speed and direction of blood flow. You may need to have medicine injected into your penis (intracavernosal injection) to cause an erection before the Doppler test is done.

The results of your tests may show which kind of treatment is a good choice for you.

Click here to view a Decision Point.Erection Problems: Should I Try Injection Treatments?

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Erection Problems: Should I Take Medicine?
Erection Problems: Should I Try Injection Treatments?

Why It Is Done

Tests for erection problems are done to help find whether the cause of an erection problem is physical, psychological, or a combination of both.

Physical conditions that may cause erection problems include:

  • Problems with the nerves of the penis. Conditions such as multiple sclerosis or diabetes may cause nerve damage that affects a man's ability to have an erection. Also, surgery, injury, or radiation treatment to the pelvic area may cause damage to the nerves of the penis.
  • Problems with the blood vessels that supply blood to the penisClick here to see an illustration.. Conditions such as hardening of the arteries (atherosclerosis) may make it difficult for a man to have an erection. Activities such as long-distance bicycle riding on a hard, narrow saddle may increase a man's risk for having an erection problem.
  • Low levels of hormones, such as testosterone or thyroid hormones.
  • Side effects of medicines, such as medicines taken for high blood pressure (hypertension) or depression.
  • The use of tobacco, alcohol, or illegal drugs.

Psychological tests may be needed if no physical cause is found for an erection problem. Psychological causes of erection problems may include:

  • Anxiety about sexual performance.
  • Relationship problems.
  • Stress.
  • Depression or grief.

How To Prepare

Nocturnal penile tumescence (NPT) test

Do not take any medicines that cause an erection, such as sildenafil (for example, Viagra), tadalafil (for example, Cialis), and vardenafil (for example, Levitra), before the test.

Do not drink alcohol or take sleeping pills for 2 days before you have a nocturnal penile tumescence (NPT) test. The alcohol and the pills can change your deep (REM) sleep time, which can affect nocturnal erections.

Intracavernosal injection test

If you are having an intracavernosal injection test, tell your doctor if you:

Doppler ultrasound

You may be asked to avoid products that contain nicotine (cigarettes, chewing tobacco) for 30 minutes to 2 hours before the test.

How It Is Done

Nocturnal penile tumescence (NPT) test

It is helpful if you wear briefs-type underwear (not boxer shorts) with a fly front when you are ready for bed. Put your penis through the fly front and keep your pubic hair inside the underwear out of the way. Put the device around your penis. After you put the device on, carefully put your penis inside your underwear.

The types of devices you can use include:

  • Snap gauge. A snap gauge is a ringlike device made up of plastic films that fit around the penis. The films break at certain pressures. A snap gauge will break during an erection. It can also tell how firm the penis became during the erection. This test is usually done 2 or 3 nights in a row.
  • Electronic devices. Electronic devices measure changes in the fullness of the penis. The devices have one or more elastic loops that fit around the penis. These are hooked to a small unit that records changes as the loops are stretched.

Intracavernosal injection test

The intracavernosal injection test is generally done by a urologist in the office or clinic. For this test, you will need to take off all of your clothes below the waist, and you will be given a cloth or paper gown to use.

While you sit or stand, your penis will be cleaned with a special soap. Then your doctor will inject a medicine into the side of your penis with a small needle. After the medicine is injected, your doctor may massage the penis for a few seconds to help spread the medicine in the penis. Some doctors may use a band that is gently tightened around the base of the penis for 5 minutes after the medicine is given to make sure an erection occurs.

A low dose of the medicine is used at first. If the low dose does not cause an erection, then a larger dose may be used. An erection should occur within 5 to 10 minutes after the medicine is given.

The medicine may also be given in a thin tablet that is put in the urethra.

After the medicine is given, you may be asked to watch sexually stimulating movies or to massage your penis to cause an erection. Your doctor will measure how rigid and how long the erection lasts. After the test, your doctor may inject a second medicine to make sure your erection goes away.

Doppler ultrasound

The Doppler ultrasound test is done by a urologist or ultrasound technician.

You will lie down on an examination table. Your doctor may need to inject a medicine or use a soft band around the penis to cause an erection to see blood flow through the vessels.

How It Feels

Nocturnal penile tumescence (NPT) test

A nocturnal penile tumescence (NPT) test does not cause any discomfort, but you may feel embarrassed about doing the test. Remember that it's important to find the cause of your inability to have an erection and you don't need to feel embarrassed about the test.

Intracavernosal injection test

During the intracavernosal injection test, you will feel a sharp, stinging pain in your penis from the needle. If you feel a burning or aching pain during the erection, tell your doctor immediately.

Doppler ultrasound

The ultrasound does not cause any pain. If you get a medicine or device during the test to cause an erection, you may feel embarrassed and the shot may hurt.


Nocturnal penile tumescence (NPT) test

There are no problems from having the nocturnal penile tumescence (NPT) test.

Intracavernosal injection test

The intracavernosal injection test has a small chance of causing:

  • Bleeding at the injection site.
  • Bruising or swelling around the injection site.
  • An erection that lasts for 3 or more hours. This condition, called priapism, is a rare side effect of some medicines used for this test. If priapism occurs, it usually can be reversed using another medicine.

Doppler ultrasound

There are no problems from an ultrasound test. If a device is used to cause an erection, you may have some mild discomfort. If a shot of medicine is used, you have the same chance for problems as the intracavernosal injection test.


Tests for erection problems can help find a cause for a man's problem in having or maintaining an erection (erectile dysfunction, or impotence).

Tests for erection problems may include blood tests for testosterone, luteinizing hormone, prolactin, and thyroid hormone. A urine test, complete blood count, blood sugar level, and cholesterol and triglyceride levels may also be done.

To learn more about lab tests done for erection problems, see:

Nocturnal penile tumescence (NPT) test

An erection has likely occurred if:

  • One or more films on the snap gauge have broken.
  • The electronic device has recorded an increase in penis size.

An erection has likely not occurred if:

  • None of the films on the snap gauge have broken.
  • The electronic device has not recorded an increase in penis size.

The test is more accurate if repeat tests show the same results.

Intracavernosal injection test

An erection caused by intracavernosal injection is usually measured on a scale of 0 to 4, with a full erection measuring a 4.

  • If the test causes an erection with a value of 3 or 4, it is likely that your erection problems do not have a physical cause.
  • If the test causes an erection with a value of 0 to 2, your erection problems may have a physical cause.

Doppler ultrasound

The ultrasound can show if you have blood flow problems as the cause of your erection problems.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Anxiety or pain while having the intracavernosal injection test.
  • Sleep problems or the use of sleeping pills.
  • The use of tobacco, alcohol, or illegal drugs.

What To Think About

  • Your doctor may do a digital rectal examination to check your prostate gland. To learn more, see the topic Digital Rectal Examination (DRE).
  • Doppler ultrasound may not be widely available. To learn more, see the topic Doppler Ultrasound.
  • Occasional erection problems are normal. If you are usually able to have and maintain a full erection, tests are usually not needed. Your erection problem may be from stress or anxiety or relationship problems.
  • Psychological tests may be recommended if no physical cause is found for your erection problem. You may want to see a counselor who specializes in sexual problems.
  • An angiogram may be recommended if initial tests can't find a cause for your erection problems. An angiogram is an X-ray test that takes pictures of the blood flow in an artery. To learn more, see the topic Angiogram. Experts are not sure how useful the angiogram test is because treatment to repair the blood vessels of the penis will be a choice for only a few men with this specific problem.
  • Dorsal nerve conduction test, evoked potential studies, and penile biothesiometry are extensive neurologic tests to check the nerve supply to the penis. These nervous system tests are not generally done or are not widely available.

Other Places To Get Help


National Kidney and Urologic Diseases Information Clearinghouse
3 Information Way
Bethesda, MD 20892-3580
Phone: 1-800-891-5390
TDD: 1-866-569-1162
Fax: (703) 738-4929
Email: [email protected]
Web Address:

The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) provides information about diseases of the kidneys and urologic system to people with these problems and to their families, to health professionals, and to the public. NKUDIC answers inquiries; develops, reviews, and distributes publications; and works closely with professional and patient groups and government agencies to coordinate resources about kidney and urologic diseases.

NKUDIC, a federal agency, is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). NIDDK is part of the National Institutes of Health under the U.S. Department of Health and Human Services.

Urology Care Foundation: The Official Foundation of the American Urological Association
1000 Corporate Boulevard
Linthicum, MD 21090
Phone: 1-800-828-7866
Phone: (410) 689-3700
Fax: (410) 689-3998
Email: [email protected]
Web Address: is a website written by urologists for patients. Visitors can find specific topics by using the "search" option.

The website provides information about adult and pediatric urologic topics, including kidney, bladder, and prostate conditions. You can find a urologist, sign up for a free quarterly newsletter, or click on the Urology A–Z page to find information about urologic problems.

Related Information


Other Works Consulted

  • Bella AJ, Lue TF (2008). Male sexual dysfunction. In EA Tanagho, JW McAninch, eds., Smith's General Urology, 17th ed., pp. 589–610. New York: McGraw-Hill.

  • Burnett AL (2012). Evaluation and management of erectile dysfunction. In AJ Wein et al., eds., Campbell-Walsh Urology, 10th ed., vol. 1, pp. 721–748. Philadelphia: Saunders.


ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerChristopher G. Wood, MD, FACS - Urology, Oncology
Last RevisedMay 14, 2012

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