Trial lawyers are a big reason health-care costs are on the rise, American Medical Association President J. James Rohack told a group of Harvard Business School alumni yesterday.

Because the nation’s legal system rewards those lawyers who pursue claims against physicians, to protect themselves doctors frequently order expensive, and sometimes unnecessary, tests for their patients.

“You don’t want to be second-guessed two years down the line, so you order that CAT scan,” Rohack said at Harvard Business School’s 10th annual gathering for alumni who work in the health-care industry.

The AMA has endorsed the latest version of the House health-care reform bill, which includes a defensive medicine buffering provision.

The Obama administration plans to include $25 million in grants into the reform bill that states and health-care systems could use to experiment with alternatives to liability lawsuits. One model would set aside $3 million a year for providers to draw from if a medical mistake is made.

“If you don’t give us protection over not ordering that CAT scan, we are going to keep ordering it,” Rohack said.