A report by Boston area doctors is encouraging patients who suspect they may be allergic to penicillin to verify their allergy by getting re-tested.

One in 10 Americans say they have an allergy to penicillin, one of the most effective antibiotics in treating infection. But researchers have discovered that patients who suspect a penicillin allergy aren’t always truly allergic.

“Data has been coming out that when we were testing these patients, they weren't allergic 95 percent of the time," said Dr. Kimberly Blumenthal, a drug allergy researcher at Massachusetts General Hospital and an assistant professor at Harvard Medical School who co-authored the report. "So, there was a big disconnect between all the patients considering themselves allergic and the patients who were truly allergic.”

Blumenthal is one member of a collaborative group of MGH doctors and others who studied the issue by reviewing 10 years of previous studies about allergies to penicillin. In their following report, they found that some people who had previously been told they were allergic to penicillin either never had an allergy or no longer were allergic. Even if someone once had an allergy or negative reaction to penicillin, the researchers found, that allergy can — and often does — subside over time.

As a result of the report's findings, which were published in the Journal of the American Medical Association in January, MGH is expanding their number of on-site allergy testing suites to allow for what they hope will be an increase in the number of patients getting tested. The goal is to have patients who do not truly have a penicillin allergy be able to once again take penicillin, which is often the best line of defense against infections.

Elaine Kauffman of Boston is considering a partial knee replacement and her doctor is concerned about infection. The 77-year-old thought she was allergic to penicillin, which is often the first medication doctors and nurses dispense to fight off bacterial infections.

“About 20 years ago,” Kauffman said, ”I had taken penicillin and I went into an anaphylactic shock and had to be rushed to the hospital, and was in the hospital for days.”

Kauffman was told never to take the antibiotic again. But her knee surgeon questions her allergy.

“So, he wanted me to get tested for penicillin because he said [with] penicillin, sometimes the allergy goes away after a number of years," she said. "And he wants to know what he can give me in case I get an infection.”

She eventually worked up the courage to get tested. She underwent both scratch skin testing and an oral dose of penicillin under supervision. Doctors found she no longer had the allergy.

Suspected penicillin allergies are a widespread problem and a potential public health threat, Blumenthal said, because if a patient is unable to take penicillin, that also eliminates their ability to take other related antibiotics, such as amoxicillin and Augmentin.

“We've actually measured the harm that that causes,” Blumenthal said,” because the alternative drugs are often less effective, more toxic, [and] cause side effects.”

Dr. Aleena Baneriji is the training program director of the allergy/immunology fellowship program at MGH. At the hospital's lab, she said, patients can undergo skin and allergy testing under the guidance of nursing care to find out if their allergy is real.

“Within a very short period of an hour to an hour and a half, we’re able to evaluate the patient and safely tell them they’re not allergic to penicillin so they can get optimal treatment,” Banerji said.