Numerous consensus meetings have attempted to formulate best-practice guidelines to diagnose and treat ED patients. The International Consultations on Sexual Medicine was one such series of meetings, first convened in 1999 with subsequent conferences in 2004, 2009 and 2015. This eventually reflects the interest of clinicians to achieve the optimal diagnostic and therapeutic tools to mange patients with ED. The goal-directed approach was combined with evidence-based practice to create diagnostic and therapeutic algorithms and establish standard-of-care practices [2, 78]. A two-level diagnostic approach is a logical guide for treating patients with ED. Currently, a tailored diagnostic pathway with full consideration of the patient’s goals is recommended. Lue [2] proposed the “goal-directed approach to diagnose and treat ED” more than 20 years ago, and this approach is still valid. In general, a detailed medical and psychosexual history that includes standardized questionnaires such as the International Index of Erectile Function (IIEF) is useful for assessing the severity of ED [79]. A thorough physical examination, although does not usually reveal the cause of ED its use is recommended to identify information of value such as Peyronie’s plaques, atrophic testes in hypogonadism, uncontrolled hypertension and neurological disorders [50]. Appropriate laboratory investigations are useful for uncovering potentially serious comorbidities. Complete blood count, fasting blood glucose, lipid profile, kidney function, and others if indicated should be obtained [80, 81]. Additional tests such as serum testosterone, prolactin, and thyroid function tests can be included at the physician’s discretion, based on the clinical scenario [82]. For an appropriate treatment the evaluation methods should address these inquiries, whether the cause of ED is organic or psychogenic; the severity and possible reversibility of ED; and the patient’s and probably the partner’s ambition and expectations. The tailored diagnosis of ED not only allows the physician to avoid further costly evaluation, but also saves the patient from invasive diagnostic techniques. Dynamic color Doppler ultrasonography of the penis is not necessary for all patients with ED. However, penile hemodynamics assessment is useful in evaluating thePDE5-Is nonresponders, young men with primary or secondary ED and a history of pelvic trauma or drug abuse, or before surgical interventions for treating PD, differentiating psychogenic from organic ED, undiagnosed penile pain with occult septal scarring and in medico-legal cases [83, 84]. Invasive diagnostic tools such as penile angiography and cavernosography/cavernosometry can be used in certain undiagnosed cases. The recent years has focused on neuroimaging, biomarkers of vascular health to further refine and personalize workup. There are ongoing investigations which stabilize the role of gene, stem cell, as well as tissue engineering therapies [85].

A multifaceted comprehensive approach is required for a full evaluation to diagnose ED. Despite the availability of innovative diagnostic tests, a detailed sexual and medical history remains the key to the diagnosis of ED. It can also differentiate between different disorders of sexual function. Psychosexual and medical history should address any unstable interpersonal relationships, or emotional stressors that can play a huge role in sexual health. Further, it should focus on the concurrent risk factors, medical comorbidities, and medications which are pivotal parts of the diagnostic evaluation. As by far the most common presenting complaint is reduction of rigidity and duration of erection rather than complete absence of erection, sexual desire and inventory of sexual partners, therefore they should also be included in history. Assessment of the onset of ED, the presence of morning erection, and any psychological conflict may help to classify psychogenic from organic ED.

Sexual history can also direct further evaluation and treatment of ED associated with other conditions especially endocrinopathy in patients who may present with a recent history of ED and low libido [80]. Early recognition of psychogenic ED not only allows the physician to avoid further costly workup, but also save the patient from unnecessary, sometime invasive diagnostic techniques. As ED is known to be associated with many risk factors, common medical comorbidities and medications, thorough inquiring may yield insights regarding peripheral vascular or coronary artery disease, diabetes, psychological, neurologic, chronic debilitating disease, or tobacco and alcohol consumption. These risk factors may direct further evaluation. Clinically, patients with multiple risk factors and medical comorbidities such as old age, long history of diabetes, and vascular disease are likely to have ED secondary to vascular and neuropathic disease [45].

On the other hand, young patients with psychiatric illness are more likely to have psychogenic or possibly secondary ED due to psychotropic medications. A patient’s past surgical history of abdomen and pelvis such as radical prostatectomy, abdominoperineal resection, pelvic trauma, and irradiation are well known to be associated with ED [86, 87].

The physical examination should focus on the vascular, neurological, and endocrine systems [91, 92]. Physical examination with particular attention to sexual and genital development may reveal micropenis, penile chordee, Peyronie’s plaque. Furthermore, small soft atrophic testes or gynecomastia may necessitate an endocrine evaluation. A careful neurologic examination should also be performed. Testing for genital and perineal sensation and the bulbocavernosus reflex is important in assessing possible neurogenic ED. Patients with certain genetic syndromes, such as Kleinfelter’s, or Kallmann’s may present with obvious physical signs of hypogonadism and a distinctive body habitus. Signs of either hyper or hypothyroidism as well as stigmata of end stage organs disorders such as liver, renal, cardiac failure should be assessed. Hypertension, arrhythmia and anemia should also be excluded. The presence of obesity noted by waist circumference, high blood pressure, or abnormal pulses may require more extensive vascular workup. In many cases, a careful history and physical examination will direct the physician to the most expedient and cost-effective approach, and eliminate the need for unnecessary diagnostic tests [93].

The laboratory investigation is directed to identify undetected medical illnesses that may contribute to ED, e.g., metabolic disturbances such as renal insufficiency, diabetes, and endocrine abnormalities (hypogonadism, hyperprolactinemia). Laboratory investigations should follow clinical suspicion of specific disorders. Hemoglobin A1c and serum glucose may be measured to detect occult diabetes, and a lipid screen performed to assess the presence of dyslipidemia [92, 94]. A complete laboratory evaluation includes serum chemistry, renal function, a complete blood count, urine analysis, and hormonal evaluation, i.e., generally serum testosterone and prolactin should be done in the initial evaluation.