How is ED diagnosed?

Patient History
Medical and sexual histories help define the degree and nature of ED. A medical history can disclose diseases that lead to ED, while a simple recounting of sexual activity might distinguish among problems with sexual desire, erection, ejaculation, or orgasm.
Using certain prescription or illegal drugs can suggest a chemical cause, since drug effects account for 25 percent of ED cases. Cutting back on or substituting certain medications can often alleviate the problem.

Physical Examination
A physical examination can give clues to systemic problems. For example, if the penis is not sensitive to touching, a problem in the nervous system may be the cause. Abnormal secondary sex characteristics, such as hair pattern or breast enlargement, can point to hormonal problems, which would mean that the endocrine system is involved. The examiner might discover a circulatory problem by observing decreased pulses in the wrist or ankles. And unusual characteristics of the penis itself could suggest the source of the problem—for example, a penis that bends or curves when erect could be the result of Peyronie's disease.

Laboratory Tests
Several laboratory tests can help diagnose ED. Tests for systemic diseases include blood counts, urinalysis, lipid profile, and measurements of creatinine and liver enzymes. Measuring the amount of free testosterone in the blood can yield information about problems with the endocrine system and is indicated especially in patients with decreased sexual desire.

Other Tests
Monitoring erections that occur during sleep (nocturnal penile tumescence) can help rule out certain psychological causes of ED. Healthy men have involuntary erections during sleep. If nocturnal erections do not occur, then ED is likely to have a physical rather than psychological cause. Tests of nocturnal erections are not completely reliable, however. Scientists have not standardized such tests and have not determined when they should be applied for best results.

Psychosocial Examination
A psychosocial examination, using an interview and a questionnaire, reveals psychological factors. A man's sexual partner may also be interviewed to determine expectations and perceptions during sexual intercourse.