Approach Considerations
The laboratory investigation for erectile dysfunction (ED) depends on information gathered during the interview. Laboratory testing is necessary for most patients, though not for all. On the basis of these study results, the physician should be able to determine the medical status of the patient, to identify and characterize the type of dysfunction, and to determine the need for additional testing (eg, penile or pelvic blood flow studies, nocturnal penile tumescence testing, or other blood tests).
Imaging studies are rarely performed, except in situations involving pelvic trauma or surgery.
In making any decisions about further management or referral, the patient’s needs, expectations, and priorities should be discussed and taken into account.
Laboratory Studies
Hormonal blood tests
According to an American College of Physicians (ACP) guideline, the evidence for the utility of hormonal blood tests in identifying and affecting therapeutic outcomes for treatable causes of ED is inconclusive. The ACP makes no recommendations either for or against routine use of hormonal blood tests or hormonal treatment in the management of patients with ED. Clinicians should make decisions to measure hormone levels on a case-by-case basis, in accordance with the patient’s clinical presentation.
Patients who express a loss of libido, depression, or any signs of diminished secondary sexual characteristics should undergo an endocrine evaluation. At a minimum, this should consist of measuring morning serum testosterone levels.
The relative merits of measuring total, free, and bioavailable testosterone levels and serum hormone–binding globulin are controversial. In screening for hypogonadism, total and free testosterone levels should be measured to investigate the hypothalamic-pituitary-gonadal axis. Testosterone levels peak at about 8 AM; thus, a morning level should be checked whenever possible. Free or bioavailable testosterone is important because it is the testosterone that is usable; the rest is attached mainly to serum hormone–binding globulin.
Measurement of luteinizing hormone (LH) may be helpful. LH levels vary according to the body’s need for testosterone. The hypothalamus regulates testosterone levels by releasing or inhibiting LH-releasing hormone (LHRH), which acts in the pituitary to produce LH. A high LH level associated with a low testosterone level implies primary testicular (Leydig cell) failure. Conversely, a low LH level associated with a low testosterone level suggests a central defect.
In some instances, prolactin levels may be helpful as well. A serum prolactin level is obtained if the patient has evidence of pituitary hyperfunction (eg, from a pituitary tumor) or if low serum testosterone levels have been documented.
A serum thyroid-stimulating hormone (TSH) evaluation is appropriate in selected patients.
Other blood tests
Additional useful screening studies include the following:
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Hemoglobin A1c
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Serum chemistry panel
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Lipid profile
These studies should be considered unless the patient has had them performed recently and the results are available.
Measurement of prostate-specific antigen (PSA) levels may be appropriate if the patient is a candidate for prostate cancer screening. Such screening is controversial, however, and should be performed only after its risks and benefits have been reviewed with the patient (see Prostate Cancer).
Urinalysis
Performing a urinalysis is recommended. The presence of red blood cells (RBCs), white blood cells (WBCs), protein, or glucose can be important clues to a genitourinary disorder.
Injection of Prostaglandin E1
A test used to evaluate penile function is the direct injection of prostaglandin E1 (PGE1; alprostadil) into one of the corpora cavernosa (see the images below). If the penile vasculature is normal or at least adequate, an erection should develop within several minutes. The patient and the clinician can judge the quality of the erection. If successful, this test also establishes penile injections as a possible therapy.
A vasodilator such as prostaglandin E1 can be injected into one of the corpora cavernosa. If the blood vessels are capable of dilating, a strong erection should develop within 5 minutes.
Erectile dysfunction. This diagram depicts a cross-section of penile anatomy and is used to instruct patients in the technique of administering intracorporeal medications.
Biothesiometry
The sensitivity of the skin of the penis to detect vibrational stimuli (ie, biothesiometry) can be employed as a simple nerve function office screening test, but it is infrequently indicated. In this test, a small electromagnetic test probe is placed on the right and left sides of the penile shaft and on the glans. The vibrational amplitude is adjusted until the subjective sensory threshold is reached, which is determined by questioning the patient (see the image below).
The presence of normal skin sensation adequate to produce an erection is measured with this device.
A series of these tests determines the average vibrational sensory threshold in each location; these thresholds are then compared with reference range standards for the patient’s age group. Although this test does not directly measure erectile nerve function, it serves as a reasonable means of screening for possible sensory deficit and is simple to perform. Formal nerve conduction studies (eg, bulbocavernosus reflex latency time) are reserved for very specific situations.
Ultrasonography
Vascular function within the penis can be evaluated by means of duplex ultrasonography. In this procedure, blood flow in the cavernosal arteries within the corpora cavernosa is measured before and after the intracavernosal injection of a test dose of a standard vasodilator (eg, 20 µg of PGE1).
Criteria for evaluating the study results vary to some degree. A peak systolic velocity lower than 25 cm/sec is generally agreed to indicate arterial insufficiency. The proposed value for the lower limit of normal ranges from 25-35 cm/sec, but a peak systolic velocity of 35 cm/sec or higher clearly rules out arterial insufficiency. End-diastolic velocity serves as a proxy for venous outflow; a velocity of 5 cm/sec or lower when the penis is at full rigidity indicates the absence of abnormal venous leakage.
Nocturnal Penile Tumescence Testing
Nocturnal penile tumescence testing involves placing several bands around the penis, connected to a device such as the Rigiscan monitor, and instructing the patient to wear the assembly for 2 or 3 successive nights. If an erection occurs, which is expected during rapid eye movement sleep, its force and duration are measured on a graph (see the image below). Inadequate or absent nocturnal erections suggest organic dysfunction, whereas a normal result indicates a high likelihood of a psychogenic etiology.
This penile tumescence monitor is placed at the base and near the corona of the penis. It is connected to a monitor that records a continuous graph depicting the force and duration of erections that occur during sleep. The monitor is strapped to the leg. The nocturnal penile tumescence test is conducted on several nights to obtain an accurate indication of erections that normally occur during the alpha phase of sleep.
Nocturnal penile tumescence testing was once frequently performed; it was thought to be useful in distinguishing psychogenic from organic impotence. Currently, other devices are available that provide similar information. Some are also able to measure rigidity (resistance to mild compression) and tumescence (size). Nocturnal penile tumescence testing is rarely used in current practice, but it can be helpful in situations where the diagnosis is in doubt.
Other Studies
Angiography is useful if the patient is a potential candidate for some type of vascular surgery. Young men with traumatic vascular injuries resulting in ED are candidates for this angiography because they may qualify for a vascular reconstruction.
In the vast majority of patients with ED, formal neurologic testing is unnecessary. However, those with a history of central nervous system (CNS) problems, peripheral neuropathy, diabetes, or penile sensory deficit may benefit from some level of neurologic testing.
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These images depict penile anatomy. Note the sinusoidal makeup of the corpora and thick fascia (ie, Buck fascia) that covers the corpora cavernosa. The major blood vessels to the corpora cavernosa enter through tributaries from the main vessels running along the dorsum of the penis.
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Vascular anatomy of the penis.
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This penile tumescence monitor is placed at the base and near the corona of the penis. It is connected to a monitor that records a continuous graph depicting the force and duration of erections that occur during sleep. The monitor is strapped to the leg. The nocturnal penile tumescence test is conducted on several nights to obtain an accurate indication of erections that normally occur during the alpha phase of sleep.
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The presence of normal skin sensation adequate to produce an erection is measured with this device.
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A vasodilator such as prostaglandin E1 can be injected into one of the corpora cavernosa. If the blood vessels are capable of dilating, a strong erection should develop within 5 minutes.
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Erectile dysfunction. This diagram depicts a cross-section of penile anatomy and is used to instruct patients in the technique of administering intracorporeal medications.
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The Medicated Urethral System for Erections (MUSE) is a small suppository placed into the urethra with this device.
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This image depicts a vacuum device used to produce an erection (also see next image). In this image, the elements are shown. They include the cylinder, a pump to create a vacuum, and a constriction ring to be placed at the base of the penis after an erection has been obtained in order to maintain the erection.
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This image demonstrates the vacuum device in place (see previous image). Note the presence of the constricting ring at the base of the penis.
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This is one of many types of constricting devices placed at the base of the penis to diminish venous outflow and improve the quality and duration of the erection. This is particularly useful in men who have a venous leak and are only able to obtain partial erections that they are unable to maintain. These constricting devices may be used in conjunction with oral agents, injection therapy, and vacuum devices.
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Two rigid cylinders have been placed into the corpora cavernosa. This type of implant has no inflation mechanism but provides adequate rigidity to the penis to allow penetration.
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This inflatable penile prosthesis has 3 major components. The 2 cylinders are placed within the corpora cavernosa, a reservoir is placed beneath the rectus muscle, and the pump is placed in the scrotum. When the pump is squeezed, fluid from the reservoir is transferred into the 2 cylinders, producing a firm erection. The deflation mechanism is also located on the pump and differs by manufacturer.
Tables
Vascular causes |
Atherosclerosis Peripheral vascular disease Myocardial infarction Arterial hypertension Vascular injury from radiation therapy Vascular injury from prostate cancer treatment Blood vessel and nerve trauma (eg, from long-distance bicycle riding) Medications for treatment of vascular disease |
Systemic diseases |
Diabetes mellitus Scleroderma Renal failure Liver cirrhosis Idiopathic hemochromatosis Cancer and cancer treatment Dyslipidemia Hypertension |
Neurologic causes |
Epilepsy Stroke Multiple sclerosis Guillain-Barré syndrome Alzheimer disease Trauma |
Respiratory disease |
Chronic obstructive pulmonary disease Sleep apnea |
Endocrine conditions |
Hyperthyroidism Hypothyroidism Hypogonadism Diabetes |
Penile conditions |
Peyronie disease Epispadias Priapism |
Psychiatric conditions |
Depression Widower syndrome Performance anxiety Posttraumatic stress disorder |
Nutritional states |
Malnutrition Zinc deficiency |
Hematologic diseases |
Sickle cell anemia Leukemias |
Surgical procedures |
Brain and spinal cord procedures Retroperitoneal or pelvic lymph node dissection Aortoiliac or aortofemoral bypass Abdominal perineal resection Proctocolectomy Transurethral resection of the prostate Radical prostatectomy Cryosurgery of the prostate Cystectomy |
Medications |
Antihypertensives Antidepressants Antipsychotics Antiulcer agents (eg, cimetidine) 5-Alpha reductase inhibitors (eg, finasteride and dutasteride) Cholesterol-lowering agents Methadone |
Treatment |
Advantages |
Disadvantages |
Semirigid or malleable rod implants |
Simple surgery Relatively few complications No moving parts Least expensive implant Success rate of 70-80% Highly effective |
Constant erection at all times May be difficult to conceal Does not increase width of penis Risk of infection Permanently alters or may injure erection bodies Most likely implant to cause pain or erode through skin If unsuccessful, interferes with other treatments |
Fully inflatable implants |
Mimics natural process of rigidity-flaccidity Patient controls state of erection Natural appearance No concealment problems Increases width of penis when activated Success rate of 70-80% Highly effective |
Relatively high rate of mechanical failure Risk of infection Most expensive implant Permanently alters or may injure erection bodies If unsuccessful, interferes with other treatments |
Self-contained inflatable unitary implants |
Mimics natural process of rigidity-flaccidity Patient controls state of erection Natural appearance No concealment problems Simpler surgical procedure than that required for fully inflatable prosthesis Success rate of 70-80% Highly effective |
Sometimes difficult to activate the inflatable device Does not increase width of penis Mechanical breakdowns possible Long-term results not available Risk of infection Relatively expensive Permanently alters or may injure erection bodies If unsuccessful, interferes with other treatments |
