"There is a high prevalence of low testosterone levels in men with erectile dysfunction," said lead author Tobias S. Köhler, MD, MPH, a urology resident at the University of Minnesota, working with Manoj Monga, MD, and colleagues. "Based on this, urologists should recognize that many of the men they are treating have androgen deficiency, and they should be on the lookout for it. These patients can be treated with hormone replacement."
Experts disagree on the definition of Androgen Deficiency in Aging Men (ADAM). The Endocrine Society defines the syndrome as a testosterone level of <200 ng/dL, or <400 ng/dL, followed by a repeat low free testosterone/bioavailable level. But it also requires that these low levels occur in conjunction with signs and symptoms that include erectile dysfunction, loss of libido, depression, lethargy, osteoporosis, regression of secondary sexual characteristics, and loss of muscle mass or strength.
The American Society of Andrology considers symptomatic men with reliable total testosterone levels <300 ng/dL to be hypogonadal, and the European Association of Urology recommends that symptomatic older men with reliable testosterone levels <346 ng/dL be considered hypogonadal.
Dr. Köhler and colleagues tried to shed some light on the controversy by retrospectively scrutinizing the records of 3,547 men who had sought treatment for ED from the Veterans Administration Health Care in Minneapolis from 1987 to 2002. The men had been offered routine laboratory tests before their initial physician visits, with the result that 2,807 had their testosterone level measured at least once. The results showed that 7% of the men had testosterone levels <200 ng/dL, 23% had levels below 300 ng/dL, 34% had levels below 346 ng/dL, and 48% had levels <400 ng/dL, Dr. Köhler reported at the Sexual Medicine Society of North America fall meeting.
The study also found that testosterone levels decreased with age. About one-third of the men had levels <400 ng/dL until 45 years of age, when the proportion rose to about half. The proportion of men with low testosterone levels stayed almost constant after that until age 80, when it exceeded two-thirds of the men. The change at age 45 is important because the Endocrine Society currently recommends checking testosterone levels starting at age 50.
But Dr. Köhler cautioned that clinicians shouldn't make a diagnosis based on a one-time testosterone check. One reason is that testosterone levels can vary, depending on the time of day.
"You should recheck the testosterone level and ask about symptoms associated with ADAM," he said.
Dr. Köhler acknowledged that his study doesn't prove that low testosterone levels are causing ED.
"It may just be that the same patients with ADAM also have ED," he said. "There could be a third factor, such as age or comorbidities such as heart disease or diabetes."
Other recent studies have found no correlation between the two syndromes.
Another factor to consider is sex hormone-binding globulin. With high levels of this substance, a patient can have normal testosterone levels, but still suffer from ADAM because the testosterone in his body is bound.
The Minnesota study confirms what many urologists have suspected, said John Mulcahy, MD, PhD, a urology consultant at Southern Arizona Veterans Administration Health Care System in Phoenix. He said he had successfully treated ED in many men with low testosterone just by replacing the hormone.
"It's something we have known anecdotally for years but have been trying to concretize," he said.
Dr. Mulcahy uses 300 ng/dL as the cutoff below which he recommends treatment with testosterone, but acknowledged that more research is needed to determine exactly when hormone replacement should be prescribed.
"It's kind of a dealer's call," he said.