More patients are checking themselves out of the hospital against their doctors’ advice, new government data shows.

The Agency for Healthcare Research and Quality reports a 40 percent increase in the number of patients who left the hospital against medical advice over a recent 12-year period. Using hospital discharge data for 2008, the agency found that 370,000 patients checked themselves out of the hospital prematurely, compared with 264,000 who made early exits in 1997.

“The staff at the hospital are saying, ‘You need to stay here,’ and patients are leaving,’’ said Anne Elixhauser, senior research scientist for the agency in Rockville, Md. “It could be that these patients are responsible for their own care, and they’re concerned about the cost of care. It may be they have other personal obligations, and they don’t have the support that they need on the outside, and they need to get back to family.’’

Although the overall numbers represent a fraction of hospital patients, the increase in early discharges is most likely an indicator of the intense pressures patients may face when they become ill.

“What discharge against medical advice really indicates is the sort of economic and social issues patients face, but that hospitals aren’t able to help with,’’ Ms. Elixhauser said.

The data comes from a national database that includes about 95 percent of hospital discharges in the United States. Last fall, the agency reported that the average hospital stay for most patients in 2008 was four days, with daily hospital bills averaging just under $7,000.