urodynamics in males with lower urinary tract symptoms showed that in the sitting position, the residual urine in the bladder was significantly reduced, the maximum urinary flow was increased, and the voiding time was decreased. For healthy males, no influence was found on these parameters, meaning that they can urinate in either position. Epidemiology Urinary retention is a common disorder in elderly males. The most common cause of urinary retention is BPH. This disorder starts around age 50 and symptoms may appear after 10–15 years. BPH is a progressive disorder and narrows the neck of the bladder leading to urinary retention. By the age of 70, almost 10 percent of males have some degree of BPH and 33% have it by the eighth decade of life. While BPH rarely causes sudden urinary retention, the condition can become acute in the presence of certain medications including antihypertensives, antihistamines, and antiparkinson medications, and after spinal anaesthesia or stroke. In young males, the most common cause of urinary retention is infection of the prostate (acute prostatitis). The infection is acquired during sexual intercourse and presents with low back pain, penile discharge, low grade fever and an inability to pass urine. The exact number of individuals with acute prostatitis is unknown, because many do not seek treatment. In the US, at least 1–3 percent of males under the age of 40 develop urinary difficulty as a result of acute prostatitis. Most physicians and other health care professionals are aware of these disorders. Worldwide, both BPH and acute prostatitis have been found in males of all races and ethnic backgrounds. Cancers of the urinary tract can cause urinary obstruction but the process is more gradual. Cancer of the bladder, prostate or ureters can gradually obstruct urine output. Cancers often present with blood in the urine, weight loss, lower back pain or gradual distension in the flanks. Urinary retention in females is uncommon, occurring 1 in 100,000 every year, with a female-to-male incidence rate of 1:13. It is usually transient. The causes of UR in women can be multi-factorial, and can be postoperative and postpartum. Prompt urethral catheterization usually resolves the problem. References External links Symptoms and signs: Urinary system Articles containing video clips Acute pain Wikipedia medicine articles ready to translate