Blood and urine testing
A key condition to exclude is undiagnosed diabetes mellitus. This is best accomplished by random measurement of blood sugar, as dipstick testing of urine to detect glycosuria does not reliably exclude the diagnosis. Because renal failure is also frequently associated with erectile dysfunction, electrolytes and creatinine should also be measured in addition to liver function tests, especially in those who admit to a high alcohol intake. Documentation of a full blood count and erythrocyte sedimentation rate is also a sensible precaution.

Evaluation of the androgen status of the patient is usually indicated, as some may respond to hormone replacement therapy.
A serum testosterone (best measured as an early-morning sample) and sex hormone binding globulin (SHBG) should be requested. In addition, if the free testosterone level is low, a prolactin level should be measured, as hyperprolactinemia is associated with erectile dysfunction and may be corrected by treatment with bromocriptine.

Some specialists also advocate testing of thyroid function, although this is a relatively unusual cause of erectile dysfunction, at least in younger men. If prostate cancer is a possibility, then a prostate-specific antigen (PSA) test should be requested, especially if treatment with androgen replacement therapy is being contemplated, as this may stimulate occult prostate cancer cells.

Nocturnal penile tumescence testing
Although still advocated by some, nocturnal penile tumescence testing is a rather cumbersome way to differentiate psychogenic from organic impotence (

Figures 45 and 46). The same information (whether or not an erection develops during sleep) may be gleaned with the use of the snap gauge device or even with a strategically located ring of postage stamps (

Figure 47). Only a few laboratories continue to employ nocturnal penile tumescence testing as a routine assessment of patients with erectile dysfunction.

Diagnostic intracorporeal injection
Injection of a vasodilator substance into one or other of the paired corpora cavernosa provides the clinician with two valuable pieces of information. First, it confirms that a normal vasodilatory response is capable of developing (although a failure to respond does not necessarily indicate organic erectile dysfunction, since the response may be inhibited by excessive nervousness). Second, this technique assesses the feasibility of self-injection pharmacotherapy as a treatment option.

Originally, papaverine, with or without the α-blocker phentolamine, was used in this context. Nowadays, PGE₁ (5–20 mg in 1 ml) is preferred (

Figure 48), sometimes in combination with other agents such as papaverine, because of a lower incidence of prolonged erectile responses and priapism.

Color duplex Doppler ultrasound assessment of intracorporeal blood flow
More precise quantitative information concerning the erectile response to intracorporeal vasoactive agents such as PGE₁  may be obtained by imaging the cavernosal arteries with color duplex Doppler ultrasonography as the erectile response develops.

Normally, the velocity of blood flow through these vessels increases rapidly in response to PGE₁ to more than 30 cm/s. As the erection develops during systole, there is forward flow whereas, during diastole, the flow is reversed because of high intracorporeal pressures. Thus, this test may help to distinguish between venous leakage and arterial insufficiency (

Figures 49, 50, 51).  

A Review of Erectile Dysfunction Arterial Blood Supply Venous Drainage Lymphatic Drainage Neuroanatomy Central Nervous System Connections - Mechanisms of erection - Causes of erectile dysfunction Vasculogenic Causes Neurogenic Causes Endocrinological Causes Priapism and Postpriapism ED Psychogenic Causes - Epidemiology of erectile dysfunction - Risk factors for erectile dysfunction - Diagnosis of erectile dysfunction History Physical Examination Special Investigations - Treatment of erectile dysfunction Psychosexual Counseling Medical Therapies Vacuum Decices Surgical Therapies - Erectile Dysfunction - Conclusions

Dynamic infusion cavernosometty and cavernosography
If veno-occlusive dysfunction is suggested by color Doppler ultrasonography investigation, then its presence and location may be confirmed by dynamic infusion cavernosometry and cavernosography (DICC). This investigation involves pre-dosing with , followed by infusion of saline with simultaneous measurement of intracorporeal pressure and flow intracavernous PGE ₁ required to maintain erection. Venous leak is characterized by an infusion of 120ml/min being necessary to maintain erection. The source of the venous leakage may be visualized by performing cavernosography using a 50:50 solution of radiographic contrast and saline. Leakage is usually visualized from the deep dorsal vein and/or the deep crural veins as well as into the corpus spongiosum of the glans. Although deep dorsal venous leakage is one of the most common appearances (

Figure 52), multiple rather than single leakage sites are the rule rather than the exception.

Functional selective pharmacopudendal angiography
Pharmacopudendal angiograms may be indicated in the relatively small number of patients whose penile Doppler ultrasound studies suggest arterial insufficiency and who are candidates for arterial reconstruction. The selective pudendal angiogram may be performed under local anesthesia and some sedation through a single femoral percutaneous puncture. The test should also include a non-selective pelvic angiogram with the catheter above the aortic bifurcation—the pelvic flush—and a selective pudendal angiogram on each side. The non-selective pelvic angiogram is used to identify lesions of the common and internal iliac arteries as well as to visualize the inferior epigastric arteries, which are the potential future donor vessels for penile bypass surgery. Occasionally, an arteriovenous fistula is detected and its embolization may restore erectile function (

Figure 53).