A person sits in a doctor's office wearing a hospital gown.

Have an elective surgery coming up? Your doctor may tell you that you need to have blood or urine tests, X-rays, or other medical tests ahead of time to detect any problems that could cause a complication during the procedure.

more on screening tests

A blood test, for instance, could reveal—at least in theory—that your blood isn’t clotting properly, which may put you at risk for excessive bleeding.

For many people, however, these preoperative screenings don’t have much benefit in practice, according to experts. “For a healthy patient having a routine, low-risk procedure, preoperative testing is generally unnecessary,” says John Vassall, M.D., a member of the Choosing Wisely Task Force of the Washington Health Alliance.

Here’s what you need to know about preoperative tests and how to talk with your doctor about them.

The Problem With Preop Testing

In decades past, preop testing was considered essential—to reveal undiagnosed conditions that might mean that a person couldn’t safely undergo surgery or that he or she might be unable to recover afterward. And some people should certainly have preop tests (see “Who Needs Preop Testing?” below). 

But today, “modern surgery is safer, and many surgeries are simpler, more routine, and less invasive,” Vassal says. Thus, routine preoperative testing isn’t likely to uncover a condition that would keep someone from having elective surgery. (In emergency surgery, there’s often no time for preop testing.)

A great deal of research backs this up. One comprehensive analysis, updated in 2016 by the U.K.’s National Institute for Health and Care Excellence (PDF), evaluated 13 types of preoperative tests—including chest X-rays, lung function tests, complete blood counts, and urinalyses—and found that in most cases, performing these tests added no benefit.

And while many preoperative tests, such as blood and urine analyses, are relatively low-risk, there’s always the chance of a false positive—a result that indicates a potential problem where there actually isn’t one, says Matthew Rusk, M.D., professor of clinical medicine at the University of Pennsylvania’s Perelman School of Medicine.

False positives can lead to additional testing, which can delay treatment and pose its own risks, or even lead to other treatments you don’t need.

For instance, a routine preop chest X-ray might detect what looks like an abnormality in the lung, which may require follow-up testing to determine whether it’s lung cancer or nothing to worry about. And a lung cancer biopsy carries the potential for serious risks, such as a collapsed lung.

Who Needs Preoperative Testing?

In general, the healthier you are and the less risky the surgery you’re having, the less likely it is that you need to do more than provide a thorough medical history and have a physical exam beforehand.

Take cataract surgery, for instance. Surgical risks such as bleeding and heart problems are highly unlikely with this procedure, Rusk says. That’s why the American Academy of Ophthalmology says that most people need no preoperative testing before having a cataract removed.

What about blood and urine tests, which are commonly ordered before a variety of surgeries? According to the American Academy of Family Physicians (AAFP) and the American Society for Clinical Pathology, these should be done only in very specific instances.

For instance, the AAFP says a preop urine test is recommended only for people who are having an invasive urological surgery or are having a device, such as a heart valve, implanted.

If you have pre-existing medical conditions such as heart disease or diabetes, or are older, you’re more likely to need some sort of preoperative testing before elective surgeries. For example, the American College of Surgeons says that most people don’t need a chest X-ray before an ambulatory (or outpatient) surgery—unless they have signs of an acute heart or lung problem, or they are 70 or older and have chronic heart or lung disease.

A complete blood count should be done only in people undergoing a major surgery who are 65 or older, or who have (or are suspected of having) anemia, according to UpToDate, an online decision-making tool for healthcare professionals.

Talking to Your Doctor

Doctors may not always be up to date on preop testing recommendations, says John C. Matulis, D.O., M.P.H., assistant professor of medicine in the division of community internal medicine at the Mayo Clinic School of Medicine. “As guidelines change, as current best practice changes, it’s hard for everyone to keep up,” he says.

You should always feel comfortable bringing up your concerns about tests and treatments, Vassall says. So if you’re having elective surgery and your doctor recommends one or more screening tests beforehand, ask a few questions. Consider these five:

  • Does the test have any risks?
  • Is it recommended for me based on my health history?
  • What is the goal of the testing?
  • What can I expect from testing?
  • How might results change my surgery or treatment?