Pneumonia patients who are under 50 and don't smoke don't need chest X-rays to look for lung cancer, suggests a new study from Canada.
The finding goes against most guidelines for pneumonia treatment, which say that patients should have the X-rays to rule out lung cancer as the hidden cause of the pneumonia.
It also comes in the midst of recent research suggesting that radiation from chest scans might increase the risk of some cancers, including breast cancer.
"If you're over 50 years of age and a smoker you do need a follow-up chest X-ray," Dr. Eric Mortensen, who has studied pneumonia and lung cancer at the University of Texas Health Science Center at San Antonio, told Reuters Health.
However, "it's important not to be exposing people who don't have a risk for (lung cancer) to added radiation," said Mortensen, who was not involved in the current study.
Dr. Sumit Majumdar from the University of Alberta in Edmonton and his colleagues followed about 3,400 patients who were treated for pneumonia in their city between 2000 and 2002.
The patients were an average age of 58, and about one in six were smokers.
Over the 3 months after they were diagnosed with pneumonia, less than half of the patients were given a chest X-ray to check for lung cancer.
Just over 1 percent of all the pneumonia patients (36 people) were diagnosed with lung cancer based on an X-ray during those 3 months - which increased to 2.3 percent (79 people) with X-rays given over the next 5 years. No patients younger than 40 got lung cancer during those 5 years of follow-up.
The researchers calculated that if all patients had been given a chest X-ray soon after pneumonia treatment, 1.7 percent of them would have been diagnosed with lung cancer. If doctors limited chest X-rays to patients 50 and older, just one case of lung cancer would have been missed and close to 3 percent of chest X-rays would have found cancer in the older population.
That suggests chest X-rays should only be done on pneumonia patients 50 years and older in order to reduce the number of X-rays done on people who are very unlikely to have lung cancer, the authors write in Archives of Internal Medicine.
They add that the cost of a chest X-ray in Edmonton is about $35, so imaging only the patients over 50 would cost $1,250 "per lung cancer detected," versus $2,125 when all pneumonia patients get X-rays.
Guidelines recommend that pneumonia patients be checked for lung cancer because the two may be closely linked.
"One of the reasons people get pneumonia is because their lungs aren't draining properly ... because there's a cancer hidden there, and it's like a sewer backing up," Majumdar told Reuters Health.
But in reality, the findings show that lung cancer is very rarely the cause of pneumonia, he said.
Mortensen said that the extra radiation given by a single chest X-ray is not a lot, but that it might as well be avoided if possible. In addition, he said, when more people who probably don't have lung cancer get chest X-rays, "We're going to find things that aren't really there," leading to more unnecessary tests or even treatment in people who don't have cancer.
"We should really figure out which populations are at risk for lung cancer and those are the ones we should be aiming (X-rays) at," Mortensen concluded. "It's added costs, it's added radiation, and if you don't need it, you don't need it."