The number of Northern California hospital stays resulting in charges of $1 million or more rose sevenfold in the past decade, from 430 in 2000 to almost 3,000 during 2010, according to a Bee review of new data from the Office of Statewide Health Planning and Development. Most of those bills will be lowered significantly—up to 80 percent—following negotiations between hospitals and insurers. Even then, they will usually still cost more than a typical Sacramento home. A recent national study in the American Journal of Medicine using 2007 data found that medical bills were a major factor in two-thirds of bankruptcy cases.