Doctors who are the most worried about malpractice suits are more likely than less fearful colleagues to order extra diagnostic tests and refer patients to emergency rooms, even if the real threat of a lawsuit is low, according to a new U.S. study reported in Reuters Health.

The practice of so-called defensive medicine “is one of those things that everyone knows goes on, but doesn’t know how to control,” said Michelle Mello, senior author of the new analysis and a professor of law and public health at the Harvard School of Public Health in Boston. The problem is a driver of excessive healthcare costs, but tackling it effectively requires a better understanding of what drives defensive medicine, Mello and her colleagues write in the journal Health Affairs.

In earlier research, Mello found that medical liability and defensive medicine accounted for approximately $55.6 billion or 2.4 percent of U.S. healthcare spending in 2008. “It’s an area where we can chip away at healthcare costs without causing pain to the patient, since these are services ordered not primarily because doctors think they’re medically necessary,” Mello told Reuters Health.

Past research has surveyed doctors about their behavior or their level of concern about malpractice, according to Emily Carrier, a senior researcher at the Center for Studying Health System Change in Washington D.C. and lead author of the new study. Other researchers have gauged the amount of defensive medicine in everyday practice by looking at insurance claims, she said.

To get a better sense of the reasons doctors may engage in defensive medicine, Carrier, Mello and their coauthors combined both approaches. The researchers started with a database of 1.9 million Medicare claims for 2008 as well as responses to a survey that same year that asked some 3,400 doctors about their malpractice concerns. Among the Medicare patients in the database, there were 29,000 who had visited an office-based physician that year for one of three complaints: chest pain, lower back pain or headache, but who were not later diagnosed with a serious illness related to that complaint. “The three complaints were chosen, in part, because each could indicate relatively minor problems, but could also suggest more severe and even life-threatening issues that would be likely to trigger testing in a risk-averse provider,” Carrier told Reuters Health in an email.

Based on the survey results, the researchers designated doctors as having a low, medium or high level of concern about malpractice, and then linked those doctors using the claims data to the tests they had ordered for patients. The team found that patients with a headache who saw a physician with a high level of malpractice concern were more likely to receive advanced imaging like a CT scan, than patients who saw a doctor less worried about malpractice. More than 11 percent of the headache patients seen by a physician with a high level of concern got additional services and testing, versus 6 percent of patients seen by a physician with a low level of concern.

Almost 30 percent of patients with lower back pain seen by a physician with high malpractice concern were given additional imaging services, compared with 18 percent of patients who saw a physician with low concern.

For chest pains, however, the less worried physicians were about malpractice, the more likely they were to order a stress test. Stress tests can involve running on a treadmill, or taking medication to make the heart work harder. Carrier said physicians who are already nervous about medical liability might avoid this test and instead choose to admit the patient to a hospital for more evaluation.

The study also found that physicians’ level of malpractice concern didn’t change, even if they were practicing in a state with medical liability reforms like caps on how much money patients can claim in damages. “Even with caps or other reform measures, it’ doesn’t make physicians feel safer,” Mello said. “We are finding that the focus should be on how physicians are feeling – that has real implications for future policies.”