The RAND IC Epidemiology Study (RICE), the largest IC epidemiology study ever undertaken, completely changed our understanding of the prevalence of IC. This survey of more than 100,000 US households told us that from 2.7 to 6.5 percent of US women may have IC, which translates to about 3 to 8 million women.

The figure is much higher than estimates from previous epidemiologic studies. The increased estimate has raised IC’s profile, attracting increased research attention, drug and device company interest, and awareness.

In 2006, the study began with research to develop a definition of IC/painful bladder syndrome (PBS), based on the medical literature and the input of top IC experts. That was tested in a survey of 599 women. Men were not included, not because anyone thought IC doesn’t occur in men, but because it’s harder to separate IC from other conditions in men based on questions about symptoms.

Because no single definition worked to identify IC, the researchers came up with two. One high sensitivity and low specificity, meaning that it indentified nearly all women with IC but also included a large number who didn’t have IC. The other had low sensitivity but high specificity, meaning that it missed more women with IC but included very few who didn’t have it. These definitions developed the basis for the questions asked in telephone surveys.

RAND researchers called some 100,000 US households—about 2,000 a week for a year—to ask a brief series of questions that would identify the households that might have one or more women living with IC. Those women were then asked to undergo a more intensive screening based on the two definitions, which would yield a range of the prevalence of IC in US women.

The results of the survey that yielded an estimate of the prevalence were presented in 2009 at the American Urological Association’s annual meeting.

Estimating prevalence was not the only purpose of RICE. The study also aims to describe the impact of IC on quality of life compared with other diseases. Some of those results have also been presented at American Urological Association meetings.

Also in 2009, a RICE study showed that IC has a huge impact on health-related quality of life and is greater than that of other pelvic conditions. IC patients’ scores on a questionnaire that helps measure health-related quality of life were significantly worse than those of the general US population and were consistently worse than scores for women with endometriosis, vulvodynia, or overactive bladder. IC patients’ lowest scores were in social functioning, bodily pain, and role limitations because of  physical problems. “These findings underscore the dramatic impact that IC/PBS has on the daily activities and well-being of these patients,” said the researchers.


Revised Tuesday, May 12th, 2015