The encouraging findings come amid larger efforts to develop a cheap, simple blood test that can quickly diagnose patients with Alzheimer’s without forcing people to undergo more expensive and invasive exams, such as spinal taps. Although blood tests are already used in clinics, they are often not covered by insurance, costing hundreds of dollars or more.

“Overall, this is a nice addition to a rapidly growing literature, although not necessarily a game changer per se,” said Cliff Abraham, a professor of neuroscience and psychology at the University of Otago in New Zealand who was not involved in the study.

The study’s authors compiled data from patients with cognitive symptoms whose mean age was 74. About 23 percent of them had subjective cognitive decline, 44 percent mild cognitive impairment and 33 percent dementia.

The authors measured the level of p-tau217, a type of protein that builds up and impairs the brain in Alzheimer’s patients, and amyloid beta, another protein that is considered a biomarker of Alzheimer’s.

“It is clear, but not surprising, that the blood test offers better diagnostic accuracy than clinical evaluation, which has access to only indirect information about brain health, for example cognitive tests,” Abraham said.

Alternatives for diagnosing Alzheimer’s include PET scans, which can cost $5,000 or more, and are not covered by Medicare except in trials, while spinal taps are invasive.

The study adds to evidence that diagnosing Alzheimer’s could soon be done more quickly and easily. Faster and more accurate diagnoses allow patients and their families to better prepare for medical bills, enroll in clinical trials or anticipate care needs, according to the Centers for Disease Control and Prevention.

Alzheimer’s is the most common form of dementia, afflicting more than 6 million Americans. Although younger people can get Alzheimer’s, most patients are elderly, with the number of patients doubling every five years beyond age 65, according to the CDC. Up to 14 million Americans may have Alzheimer’s by 2060.

The disease begins with mild memory loss but can progress to patients losing the ability to carry on a conversation. It is one of the top 10 causes of death in the United States, with death rates climbing. There is no cure, although there are drugs that can slow the disease.