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Tests for Erection Problems

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.

WebMD Medical Reference from Healthwise

Last Updated: May 14, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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