Alzheimer's patients could soon have more treatment options available. Biogen's Leqembi obtained approval from the U.S. Food and Drug Administration earlier this year, and another treatment from Eli Lilly, donanemab, may not be far behind.

The one drawback, however, is that those drugs treat Alzheimer's when the disease is in its early stages, and thus, many people won't be able to benefit from them. But there's a company that may solve that problem. Quest Diagnostics (DGX 0.54%) has a test that can help make it easier to assess the risk of developing Alzheimer's.

A test to identify Alzheimer's much earlier

On July 31, Quest launched a direct-to-consumer blood test, AD-Detect, which assesses beta amyloid protein. Amyloid beta in the brain is often associated with Alzheimer's, and the test can identify whether there are abnormal levels, which can be crucial in identifying people who have a high risk of developing the disease.

The test costs $399, and people can buy it on the diagnostic company's website. Quest previously made a blood test, which uses the same technology, available early last year, but only doctors could purchase it. Now, it's even easier for people to access the test. But a doctor will still need to review the purchase to confirm that it is medically necessary. The test is designed for people who have either a family history of Alzheimer's or who have mild memory loss.

As more treatment options become available, Quest's Medical Director of Neurology, Dr. Michael K. Racke, believes it should lead to strong demand for the test. He notes that the healthcare company is "seeing a push from consumers who have a desire to take more control of their health, including within more advanced areas like Alzheimer's disease risk assessment."

Early diagnosis is key to early treatment

In clinical trials, Leqembi was able to reduce amyloid levels in the brain, and it also slowed cognitive decline in patients with early stages of Alzheimer's by 27%. Donanemab achieved similar results, showing that it could slow the decline by 29%.

While there may not be an overwhelming difference between the two drugs, the one thing that appears to be clear is that treating the disease early on can be key to better results. Eli Lilly's Chief Scientific and Medical Officer, Dr. Daniel Skovronsky, says that "every time, it just looks like early diagnosis and early intervention are the key to managing this disease."

Should you invest in Quest Diagnostics?

Alzheimer's is a huge problem for the U.S. According to the Alzheimer's Association, an estimated 1 in 3 seniors dies as a result of Alzheimer's or dementia. And there could be 13 million Americans with the disease by 2050, which is more than double the number of people who have Alzheimer's today -- approximately 6 million.

The need to treat Alzheimer's is significant, and Quest Diagnostics could play a key role in meeting that goal. While Biogen and Eli Lilly may have the treatment options, being able to detect Alzheimer's in its early stages is going to play a key role in their overall effectiveness.

Quest generated just under $10 billion in sales last year, and it has a healthy profit margin of around 10%. At 20 times earnings, the stock is relatively cheap given the healthcare average is at a multiple of over 26.

Throw in a 2% dividend yield plus the company's potential to benefit from a big growth opportunity in Alzheimer's testing, and Quest Diagnostics could be an underrated stock to buy and hold for the long term.