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.

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 penis. 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. See an illustration of blood supply to the penis.
• 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.

Tests for erection problems includes a sexual history and physical examination. A physical examination includes checking your blood pressure. Your penis and testicles are also checked for any problems. Blood tests for testosterone, luteinizing hormone (LH), prolactin, and thyroid hormone levels are usually done. Other blood tests that may be done include a complete blood count (CBC), blood glucose, cholesterol, and triglyceride. A urine test may also be done. If these results are normal, many doctors will have you try a medicine, such as sildenafil citrate (Viagra), tadalafil (Cialis), or vardenafil (Levitra), before doing more tests.

More tests for erection problems may include a nocturnal penile tumescence (NPT) test or an intracavernosal injection test.

Nocturnal penile tumescence (NPT) test

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

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.

The NPT test sees whether a man is having normal erections during sleep. 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 is more expensive than using the snap gauge, but it is more accurate and gives more detailed information about erections during sleep. This device records how many, how long, and how rigid the erections are during sleep.