The value of routine endocrinologic testing remains controversial because the incidence of endocrinopathy presenting primarily as erectile dysfunction was thought to be low. But in a large series reported by Nickel and associates, the overall incidence of endocrinopathy in impotent patients was as high as 17.5%, and in about 12% of patients the endocrinopathy clearly contributed to the erectile dysfunction. Therefore, although endocrinopathy can certainly lead to impotence, its role may be due to its effects on central libido mechanisms rather than on the penile tissue itself.
The basic screen consists of serum testosterone and prolactin measurements.
Low serum testosterone can be a cause of erectile dysfunction. Truly low serum testosterone level is indicated by the history and physical examination, including decreased sex drive, poor erections, dry skin, small testicles, a decreased need to shave, and a decreased amount of muscle mass.
The single best test for testosterone level is the free serum testosterone. The specific testosterone assay to be obtained is debated. Testosterone is predominately protein-bound and is influenced by a variety of clinical conditions. It is secreted in a diurnal manner with a peak in the morning. Normal testosterone levels gradually decline with advancing age. An age-adjusted, first-morning, free testosterone level is probably the most accurate measure.
Raised levels of serum prolactin can present as erectile dysfunction, and serum Prolactin levels should be tested for in all cases of erectile dysfunction even if another cause os obvious, such as a patient with diabetes.
For a list of Common Causes of raised Prolactin levels, click here
Clinically, cases of truly elevated prolactin levels can be predicted from the clinical history. The key question in the clinical history is to ask about a lack of interest versus an inability to get an erection. These men will typically say that they are able to get a good erection, but they have no interest in having sexual relations.
Other laboratory tests in the evaluation of erectile dysfunction include the gonadotropins. Gonadotropins are substances produced by the pituitary gland that are useful when trying to discover the reasons for low testosterone levels. The first clinically useful test is called the luteinizing hormone, the hormone that stimulates the production of testosterone. A man with low testosterone and a low luteinizing hormone (LH) is diagnosed as hypogonadotrophic. The condition called hypogonadism is low testosterone and a high LH, which indicates testicular failure.