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.
Your doctor may want to rule this out by asking for an estimation of free serum testosterone.
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.