A U.S. company has started selling the first blood test to help diagnose Alzheimer’s disease, a leap for the field that could make it much easier for people to learn whether they have dementia. It also raises concern about the accuracy and impact of such life-altering news.

Independent experts are leery because key test results have not been published and the test has not been approved by the U.S. Food and Drug Administration — it’s being sold under more general rules for commercial labs. But they agree that a simple test that can be done in a doctor’s office has long been needed.

“I think there are two key steps that need to happen before this test really becomes more widespread,” internal medicine specialist Dr. Karen Abrashkin said Tuesday. “One is that we need to see the data that’s being used to develop the test. We haven’t seen that data yet. It hasn’t been published and so we don’t know how sensitive or specific this test is for Alzheimer’s.”

More than 5 million people in the United States and millions more around the world have Alzheimer’s, the most common form of dementia. To be diagnosed with it, people must have symptoms such as memory loss plus evidence of a buildup of a protein called beta-amyloid in the brain.

The best way now to measure the protein is a costly PET brain scan. That means most people don’t get one and are left wondering if their problems are due to normal aging, Alzheimer’s or something else.

The blood test from C2N Diagnostics of St. Louis aims to fill that gap. The company’s founders include Drs. David Holtzman and Randall Bateman of Washington University School of Medicine, who headed research that led to the test and are included on a patent that the St. Louis university licensed to C2N.

The test is not intended for general screening or for people without symptoms — it’s aimed at people 60 and older who are having thinking problems and are being evaluated for Alzheimer’s. It’s sold in all but a few states in the U.S. and just was cleared for sale in Europe.

It measures two types of amyloid particles plus various forms of a protein that reveal whether someone has a gene that raises risk for the disease. These factors are combined in a formula that includes age, and patients are given a score suggesting low, medium or high likelihood of having amyloid buildup in the brain.

While there is still no cure for the disease, Dr. Abrashkin agreed that the goal of early detection is important.

“Understanding if it’s Alzheimer’s, there’s different ways you can support people who have Alzheimer’s, and in the future there may be more treatments for this illness,” she said. “It’s equally important to understand when somebody does not have Alzheimer’s and to rule that out and to look for other causes of cognitive impairment.”

The company has not published any data on the test’s accuracy, although the doctors have published on the amyloid research leading to the test. Company promotional materials cite results comparing the test to PET brain scans — the current gold standard — in 686 people, ages 60-91, with cognitive impairment or dementia.

If a PET scan showed amyloid buildup, the blood test also gave a high probability of that in 92 percent of cases and missed 8 percent of them, said the company’s chief executive, Dr. Joel Braunstein.

Braunstein said the company will seek FDA approval and the agency has given it a designation that can speed review.

(SD-Agencies)