Occasionally forgetting what you were about to say or where you put your keys is normal, especially as you get older. But many people worry that such lapses are the first signs of Alzheimer’s disease, and more of them are turning to a high-tech — and expensive — imaging test called a PET scan to find out.

That’s often a bad idea, in part because when used inappropriately it can lead to unnecessary treatment and needless exposure to radiation. In fact, a professional group for health-care providers who perform the test is so concerned about its overuse that it recently included PET scans in a campaign that highlights unnecessary and sometimes harmful medical care. The initiative, Choosing Wisely, is sponsored by the ABIM Foundation and Consumer Reports.

Testing drawbacks

Signs of Alzheimer’s disease include plaque deposits and abnormal tangles of brain fibers. A PET scanner, which creates three-dimensional images of your brain, can find those abnormalities.

The test involves injecting a radioactive drug into your blood to highlight the deposits on the scan. If it doesn’t show plaque deposits, then you probably don’t have Alzheimer’s. But rushing to take the test without having a thorough medical exam is a mistake for a few reasons:

●Not all plaque deposits mean Alzheimer’s disease. People can have plaque deposits without any substantial memory loss, says Satoshi Minoshima, vice chair for research in the Department of Radiology at the University of Washington in Seattle. And having deposits doesn’t necessarily mean you will later develop Alzheimer’s. So a worrisome result on the PET scan might cause needless anxiety, explains Minoshima, who is also a leader of the Society of Nuclear Medicine and Molecular Imaging, the organization that included PET scans in its Choosing Wisely list.

●Memory problems can stem from other health problems. Alzheimer’s is the leading cause of memory loss and thinking problems among older people. But other medical conditions — such as a stroke, an underactive thyroid, drug interactions and side effects, alcoholism and Vitamin B12 deficiency — can cause similar symptoms. Unlike Alzheimer’s, those can be treated. So your doctor should rule them out before ordering a PET scan. That can involve some blood tests and, in some cases, possibly an MRI or CT scan. Your doctor should also ask about the drugs and supplements you take.

●The test can expose you to unnecessary risks and costs. A PET scan exposes you to a small amount of radiation. Since those effects can add up over time, it’s best to avoid radiation when you can. In addition, the test can cost several thousand dollars and is not covered by Medicare or private insurance for Alzheimer’s testing.

When it makes sense

If you have serious memory loss and your doctor can’t find a clear cause, then a PET scan can be a reasonable next step. Learning that you have early-stage Alzheimer’s can allow you and your family to consider medication and plan for the future. But note that Consumer Reports’ Best Buy Drugs report on Alzheimer’s drugs found that they don’t work well for most people and often cause side effects.

Copyright 2013. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.