Laboratory Tests for Erectile Dysfunction
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.
The laboratory evaluation should be directed by the history and physical examination findings.
The patient should be screened for any undiagnosed medical disease that may be the underlying cause of erectile dysfunction.
A urinalysis, complete blood count and basic chemistry panel will help to rule out most metabolic and renal diseases. In elderly men, because thyroid disease can present subtly, the thyroid-stimulating hormone level should be measured to rule out thyroid dysfunction. In one study of men who underwent an endocrinologic evaluation for erectile dysfunction, 6 percent were found to have hypothyroidism, and their erectile function improved with treatment.
Some authors advocate measuring prolactin and free testosterone levels as part of the initial evaluation.The value of this routine testing is uncertain, however, because the incidence of endocrinopathy presenting as erectile dysfunction is reportedly only 2 percent.
A reasonable strategy is to obtain a free testosterone level in all men aged 50 and older and in those younger than 50 who have symptoms or signs of hypogonadism such as decreased libido, bilateral testicular atrophy or a reduced amount of body hair.
The prolactin level should be measured if the free testosterone level is low, the patient has a substantial loss of libido or a prolactinoma is suspected on the basis of a history of headache with visual field cuts Measurement of luteinizing hormone levels can be reserved for use in distinguishing primary from secondary hypogonadism in men with low testosterone levels.
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.
