Tests for Erection Problems

Test Overview

Tests for erection problems can help find out why a man can't have or maintain an erection. This problem is called erectile dysfunction, or impotence. It's a common male problem. Most erection problems are caused by a mix of blood vessel, nerve, or psychological issues.

To find the cause, your doctor will first ask about your sexual history and do a physical examination. During this examination, the doctor will:

  • Check your blood pressure.
  • Check your penis and testicles for any problems.
  • Order blood tests to check hormone levels.

Other tests that may be done as part of the examination include:

If the results of your physical examination and other tests are normal, your doctor may have you try a medicine that helps cause an erection. If the medicine doesn't help, then you may need more tests.

This topic focuses on three more tests you may have after the physical examination and lab tests listed above. These three tests are:

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

Nocturnal penile tumescence (NPT) test

The NPT test checks to see if a man is having normal erections during sleep. Most men have 3 to 5 full erections during deep sleep. Men who don't have erections because of psychological problems can still have erections during deep sleep. Sometimes, sleep problems or serious depression can prevent these normal nighttime erections.

This test can be done at home or in a special sleep lab.

Tests are usually done for at least 2 nights in a row. If good erections occur during sleep, the cause of the erection problems is most likely 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 into the side of the penis to make an erection. The fullness of the erection and how long the erection lasts are measured.

Doppler ultrasound test

Doppler ultrasound uses a handheld tool that is passed gently over the penis. The tool uses reflected sound waves to show blood flow on a computer screen.

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

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Why It Is Done

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

Physical causes include:

  • Problems with the nerves of the penis. Problems such as multiple sclerosis or diabetes may cause nerve damage. Surgery, injury, or radiation treatment to the pelvic area can also damage the nerves of the penis.
  • Problems with the blood vessels that supply blood to the penis. Hardening of the arteries (atherosclerosis) can limit blood flow. And 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 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

Before the test, do not take any medicines that cause an erection. These medicines include sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra).

Do not drink alcohol or take sleeping pills for 2 days before you have an NPT test. The alcohol and the pills can change your deep sleep time. This can affect nighttime erections.

Intracavernosal injection test

Tell your doctor if you:

  • Are allergic to any medicine.
  • Take a blood thinner, or if you have had bleeding problems.
  • Have ever had an erection that lasted more than 3 hours.

Doppler ultrasound

You may be asked to avoid products with 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. Keep your pubic hair inside the underwear out of the way. Put the device around your penis. After you put on the device, carefully put your penis inside your underwear.

The types of devices you can use include:

  • Snap gauge. A snap gauge is a ring-shaped device made 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. These devices measure changes in the fullness of the penis. They 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

This 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. 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. 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. The band is 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.

A similar medicine may also be placed into the urethra, the tube through which urine leaves the penis. This is called an intraurethral injection.

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 arousing movies or to massage your penis to cause an erection. Your doctor will measure how rigid the erection is and how long it 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. This lets the doctor see blood flow through the vessels.

How It Feels

Nocturnal penile tumescence (NPT) test

An NPT test does not cause any discomfort. But you may feel embarrassed about doing the test. Remember that it's important to find the reason you are not able to have an erection. You don't need to feel embarrassed.

Intracavernosal injection test

During the test, you will feel a sharp sting in your penis from the needle. If you feel a burning or aching pain during the erection, tell your doctor right away.

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. The shot may hurt a bit.


Nocturnal penile tumescence (NPT) test

There are no problems from having the NPT test.

Intracavernosal injection test

This 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. It is a rare side effect of some medicines used for this test. If this occurs, it can likely be reversed with 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 pain. 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 out why a man can't have or maintain an erection. This problem is called 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.

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 is usually measured on a scale of 0 to 4. A full erection is 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

You may not be able to have the test, or the results may not be helpful, if:

  • You feel anxious or have pain during the injection test.
  • You have sleep problems or use sleeping pills.
  • You use 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.
  • Random erection problems are normal. In most cases, if you can have and maintain a full erection, tests may not be needed. Your problem may be from stress or anxiety or relationship problems.
  • Your doctor may suggest psychological tests if no physical cause is found for your erection problem. You may want to see a counsellor who specializes in sexual problems.
  • An angiogram may be suggested if tests can't find a cause for your erection problems. This 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 this test is. That's 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 tests, 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 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.


Current as of: May 28, 2019

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Christopher G. Wood MD, FACS - Urology, Oncology

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