According to a recent study from the Archives of Internal Medicine, primary care physicians are referring more patients to specialists than ever before. In fact, the rate almost doubled in the 10-year period between 1999 and 2009.

This drives up the cost of care, as specialist consults tend to be more expensive than primary care visits.  Furthermore, specialists tend to order more advanced diagnostic tests.

It’s pretty easy to see why this is happening.

Back in the days of capitated care, there was pressure from HMOs to reduce the amount of referrals, as doctors were given a set fee to manage each patient. A referral meant a financial hit to the practice.  But the HMO model was rejected by patients, who didn’t like their choice restricted and accused doctors of holding back care.

So, fee-for-service medicine continued to grow, and there was little incentive to scale back referrals. In fact, as a New England Journal of Medicine study revealed a few years ago, the Medicare patients saw an average of seven doctors: 2 PCPs and 5 specialists.

According to the lead author of the Archives study, Dr. Bruce E. Landon,

… medicine has become more complex, with specialists and subspecialists seen as expert in the latest treatments. “Medicine is becoming increasingly technologically sophisticated,” he said in an interview.

But Dr. Landon also points to the “tyranny of the 15-minute visit,” during which the average primary-care physician does not have the time or resources to delve into any potentially complicated medical condition.

The last point rings particularly true. As patients become more complex and time pressures grow, many doctors simply take the path of least resistance and refer out.

Sarah Kliff, who blogs at the Washington Post’s progressive-leaning Wonkblog, adds that money is a factor:

… part of it likely has to do with the economics of referrals: Doctors who have an ownership stake in their practice are 50 percent more likely to refer to a specialist, which would increase the total revenue generated by a given patient.

That’s dubious.  I don’t have a financial incentive to refer to specialists.  Most of my colleagues don’t either.  And with more doctors exiting private practice and into salaried hospital positions, that reason will become less relevant.

I’ll add one more reason that hasn’t been mentioned: defensive medicine. Although the threat of a malpractice lawsuit is typically associated with ordering potentially unnecessary tests, making a specialist referral is simply another variation. When primary care doctors see “failure to refer” as one of the leading reasons why they get sued, it’s no wonder why more are doing so.

Physician behavior is governed, to a large degree, by incentives. Given the incentives that doctors face in our health system today, there’s little surprise why more are referring patients out to specialist care.

Kevin Pho is an internal medicine physician and on the Board of Contributors at USA Today.  He is founder and editor of KevinMD.com, also on Facebook, Twitter, and LinkedIn.