A new study by the University of Texas Medical Branch found that 20 percent of men were prescribed testosterone despite having normal testosterone levels based on the Endocrine Society’s guidelines. The study also found that 39 percent of new testosterone users did not have a prostate cancer screening during the year before treatment and 56 percent were not screened during the year after starting treatment.

The study comes at a time when there has been a dramatic increase in testosterone prescriptions in men over 40 within the past decade as they seek to increase muscle tone and sex drive. However, the long-term risks of this treatment are not well understood.

The Endocrine Society has formally recommended that testosterone therapy only be prescribed to men with low testosterone levels and no signs of prostate cancer.

The UTMB study of more than 61,000 men from across the nation is the first to survey how many men with normal testosterone levels begin testosterone therapy and rates of prostate cancer screening before and during the therapy.

The population-based study examined health insurance data from 61,474 men 40 years or older treated with testosterone between 2001 to 2010. It appears in the Feb. 26 issue of Public Health Reports.

The UTMB analyses also showed that 25 percent of men included in the study did not have their testosterone levels checked before receiving a prescription. Nearly half of these men did not have their levels checked during the first year of treatment.

“These findings show that there may not be a consensus among physicians regarding the definition of ‘low testosterone,’ said Jacques Baillargeon, UTMB professor of epidemiology in the department of Preventive Medicine and Community Health and lead author of the study. “It’s possible that in some cases physicians judge that a patient’s symptoms, such as fatigue and loss of muscle mass, merit testosterone therapy without clinically defined low testosterone levels.”

The study also found that 39 percent of new testosterone users did not have a prostate cancer screening during the year before treatment and 56 percent were not screened during the year after starting testosterone treatment.

Baillargeon said that the low rates of prostate cancer screening were surprising because, according to Endocrine Society guidelines, screening is recommended for all men before starting testosterone therapy.

Many testosterone users did not see a urologist or endocrinologist before or during treatment and thus were less likely to receive care based on Endocrine Society guidelines.

“These findings are very important from a medical and public health standpoint given the rapidly increasing number of men receiving testosterone in the U.S.,” said Baillargeon. “Further research on the medical decision-making processes involved in monitoring and prostate cancer screening will be important, given our limited knowledge of the risks of this therapy.”

The other authors of this paper include Randall Urban, Yong-Fang Kuo, Mukaila Raji, Bret Howrey, Yu-li Lin and Kenneth Ottenbacher at UTMB; Holly Holmes at the University of Texas M.D. Anderson Cancer Center and Abraham Morgentaler at Harvard Medical School. This paper was supported by the National Institutes of Health.