Physician assistants are everywhere. Should you see one?

In the last 25 years, the medical work force has undergone something of a transformation: The number of physician assistants has quadrupled.

You’d be forgiven if you haven’t noticed the shift — or if you’ve mistaken a P.A. for a medical doctor. P.A.s often wear white coats and have the authority to prescribe medications, make diagnoses and manage treatment plans.

So how do they differ from M.D.s, and is it OK if you see a P.A. for your medical care?

WHAT IS A P.A.?

When the role was first created in the 1960s, physician assistants were meant to help expand access to health care in rural America by acting as an “extra right hand” for physicians, performing routine tasks, like taking patient histories and performing physical examinations, under the close supervision of a doctor.

The profession has changed substantially since then: Today, P.A.s practice in every medical specialty and with far more independence.

Still there are some key distinctions between doctors and P.A.s. One of the clearest differences is that doctors have more professional training.

While doctors spend about four years in medical school and an additional three to seven years receiving specialty training, physician assistants typically attend a two- to three-year masters program.

In most of the United States, P.A.s are still legally required to work with oversight from a doctor. But just how closely a P.A. works with a physician depends heavily on the medical specialty, state laws and the individual practice.

In surgical specialties, for example, P.A.s often work alongside doctors, controlling bleeding, removing tissue and stitching the patient up. They are not permitted to perform major surgeries independently.

But in primary care, physician assistants have far more autonomy. They can diagnose, prescribe medications and create management plans without a doctor in the room. States differ on the level of doctor supervision required in primary care. In some, the doctor must be within 30 miles of where the P.A. is practicing. In others, the doctor can be remote with little or no mandated checks.

The American Academy of Physician Associates, a professional society representing P.A.s, has recently pushed to untether the profession from doctors and to change the title from physician assistant to physician associate.

The organization has lobbied state legislators to change laws so that P.A.s will be allowed to practice more independently. The organization argues this will shorten appointment wait times and drive down health care costs. The American Medical Association, the national group representing doctors, has argued that P.A.s “do not have the same skill set as physicians” and that allowing them to practice without doctor oversight could risk patient safety.

P.A.s should not be confused with nurse practitioners, another growing group of nonphysician providers who similarly have the authority to prescribe, diagnose and manage care. The two providers typically attend masters programs that are roughly the same length, but N.P. programs tend to be more specialized in one area of focus, like orthopedics or oncology, whereas P.A.s are taught a more general curriculum that is modeled on medical school.

Nurse practitioners also have far more autonomy to practice without physician oversight once they graduate. More than 20 states let N.P.s prescribe, diagnose and treat patients without physician supervision, and more than a dozen more only require doctor oversight for writing prescriptions.

DOES IT MATTER IF MY PROVIDER IS A P.A.?

When you’re seen by a P.A., do you get the same quality of care as when you’re seen by a doctor?

After several deaths linked to P.A. care set off a national debate over whether the providers should be allowed to practice independently in Britain (where the profession was far less regulated than in the U.S.), a group of researchers set out to answer this very question, reviewing 40 studies that compared the safety, effectiveness, efficiency and other measures of doctors with those of P.A.s. A vast majority of the studies were conducted in the United States.

Several studies, they found, suggested that access to health care improved when a P.A. was added to a medical team, potentially avoiding dangerous delays in treatment — though it’s unclear whether increasing staffing of any kind would have had the same effect. One study found that when a P.A. who specialized in geriatric medicine began routinely seeing nursing home residents as part of a physician-led team, annual hospital visits fell by 38 percent.

And when P.A.s worked closely with doctors, whether that was assisting with surgery or working on a team in the hospital, the care was consistently high quality. The research also showed that P.A.s who met regularly with patients to answer questions and fill prescriptions were good at helping patients manage chronic conditions, like diabetes.

But in situations where P.A.s had less oversight from a physician and were primarily responsible for making diagnoses, the research was far less conclusive, said Dr. Nicola Cooper, who studies diagnostic error and patient safety at the University of Nottingham School of Medicine and led the study.

“There’s not a lot of high quality evidence” Dr. Cooper said, partly because researchers measure harm in medical care mainly by looking at malpractice lawsuits and deaths, both of which are exceedingly rare in primary care given that providers mainly see patients with minor illnesses.

And evaluating other metrics of quality, like diagnostic errors and prescribing practices, is not always comparing apples to apples, since P.A.s are sometimes assigned more straightforward cases than the ones doctors handle.

Some experts pointed out that the question is moot, since many Americans don’t live where doctors are readily available. Often what matters is access to any provider at all.

“Quite frankly, if the patient’s needs are met, they’re satisfied,” said Roderick Hooker, a P.A. who studies the medical work force. “They don’t care who delivered it, as long as they were taken care of.”

The article originally appeared in The New York Times