At least 400 million people lack access to essential health services, the World Health Organization and World Bank said Friday in a new report that they described as a “wake-up call” about the challenges to achieving universal health coverage.

The report also said that at least 6 percent of people in 37 low-and-middle-income countries are living in poverty because of the money they must spend on health. That finding alone suggested that the poorest could be left further behind by rising global health costs.

“The world’s most disadvantaged people are missing out on even the most basic services,” Dr. Marie-Paule Kieny, assistant director-general for health systems and innovation at the W.H.O., said in a statement announcing the 98-page report, which was released online and at a news conference at United Nations headquarters in New York.

Dr. Timothy G. Evans, senior director of health, nutrition and population at the World Bank Group, said the report’s findings illustrated the vulnerability of the world’s poorest people to health expenses.