A detailed medical and psychosexual history and a thorough physical examination are the most important steps in the differential diagnosis of sexual dysfunction. Interviewing the partner, if available, is very helpful in eliciting a reliable history, planning treatment, and obtaining a successful outcome. ED is often associated with a variety of diseases such as diabetes mellitus, coronary artery disease, hyperlipidemia, hypertension, spinal cord compression, and pituitary tumor. Therefore, a routine workup aimed at determining the cause should be performed in all patients. This should include basic laboratory tests such as a complete blood count, urinalysis, fasting blood glucose, serum creatinine, lipid profile, morning serum testosterone, and prolactin levels. The physician should then assess the findings, inquire about the goals and preferences of the man (and his partner), and discuss further diagnostic and therapeutic options so that his (or their) participation in the decision-making process will be well informed (_{Lue, 1989}). Some men may benefit from a referral for further testing and treatment. The indications for referral include complex gonadal or other endocrine disorders; neurologic deficit suggestive of brain or spinal cord disease; deep-seated psychologic or psychiatric problems; and active cardiovascular disease, especially if the patient wishes to take sildenafil. If the man is taking a drug known to cause ED or recreational drugs, or has vascular risk factors, a change in medication or lifestyle may be helpful.

A variety of self-report measures for assessing the levels of male sexual function are now available. The most commonly used is International Index of Erectile Function (IIEF) (_{Rosen et al, 1997}). It has 15 items and addresses and quantifies 5 domains: erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction (_{Rosen et al, 1997}). An abridged 5-item version of the IIEF has also been developed for office use (_{Rosen et al, 1999}). ED severity is classified into 5 categories based on the IIEF 5: severe (5-7), moderate (8-11), mild to moderate (12-16), mild (17-21), no ED (22-25).

In patients with complicated problems, a variety of vascular and neurologic tests are available to further identify the cause of ED (

Table 37-4). These are discussed below.