Medical visits for gender identity disorder have surged roughly 45 percent in three years and totaled 22,435 as of the end of 2015, a survey showed Saturday.

The survey by the Japanese Society of Psychiatry and Neurology compiled data from 26 hospitals and clinics across the country. The group estimates that the actual number of transgender people in Japan is higher than 25,000 because some of the patients may not have been treated at the designated institutions.

The number of people diagnosed with GID who arranged hospital visits rose by about 7,000 compared with the previous estimate in 2012, the group said.

One expert said the number of transgender people in Japan is much bigger when accounting for children, students and the elderly, who have stayed away from medical institutions.

Of the 22,435 patients, 14,747 were registered as female at birth but identify as male, and 7,688 the opposite, according to data provided by Katsuki Harima, a doctor on the group's GID committee.

"It is important to share the number of patients as it could lead to deeper understanding of them and eliminate secondary victimization, such as discrimination and bullying," said Mikiya Nakatsuka, a professor at Okayama University's Graduate School of Health Sciences. Nakatsuka heads the Japanese Society of Gender Identity Disorder.

A law was enacted in 2004 to pave the way for Japanese to officially change their registered sex in certain conditions. About 6,000 people had done so by the end of 2015.

While doctor consultations are on the rise, some GID patients are believed to be holding back because of financial reasons or fear of discrimination.

According to Nakatsuka, gender reassignment surgery, one of the criteria for officially changing one's sex, costs more than ¥1 million ($8,900), partly because it is not covered by public health insurance.

Some experts estimate that there are about 46,000 people in Japan with GID.