A glimpse into the future may already be flowing through our veins.

In a major breakthrough, researchers have developed a simple blood test that may one day help doctors predict how fast early-onset dementia will progress.

“[It] can give us a window into how aggressively the disease is likely to behave — and that’s information that up to now, we really didn’t have,” Dr. Liron Sinvani, director of research and innovation for the Northwell Institute of Healthy Aging Institute, who was not involved in the study, told The Post.

Early signs suggest the test may also offer insight into the type of dementia a person has — something Sinvani called a “game changer” for patients and their loved ones.

“When we talk about dementia, most people think of someone in their 80s and 90s, but early-onset dementia strikes people in their 50s and 60s,” she said. “People are still working, raising families and planning for the future.”

Having a blood test that can help doctors identify the type of dementia a person has and the speed it may progress may give those affected a better idea of what they’re facing.

“[We’ll be] able to better prognosticate, so families can have a clearer picture of what the trajectory is likely to be, enabling better planning for care, for work, for finances, for legal matters,” she said.

In the study published Wednesday in JAMA Network Open, researchers in South Korea followed 322 men and women with early-onset Alzheimer’s or frontotemporal dementia (FTD) and an average age of 62.

At the outset, participants underwent extensive physical and neurological exams, including blood tests. Those tests were repeated annually over two years, allowing scientists to track key changes over time.

The researchers focused specifically on three biomarkers in the blood: p-tau217, GFAP and neurofilament light chain.

By the end of the study period, the team found that in patients with early-onset Alzheimer’s, all three biomarkers accurately predicted how quickly patients declined cognitively and functionally.

“With these three biomarkers, having a higher level meant faster worsening,” Sinvani said.

“So not only is it predicting based on the level who is going to get worse faster, but also checking it over time, the rising levels basically tracked with clinical progression, really showing the association between this blood level and their cognitive and functional status,” she continued.

Things were slightly different with FTD.

In those patients, only two markers — GFAP and neurofilament light chain — were tied to cognitive decline. The third, p-tau217, did not show the same link.

That, Sinvani said, signals that the p-tau217 biomarker is specific to Alzheimer’s.

“What the study shows is that a simple blood test may help clinicians predict not only who will decline faster, but it also distinguishes between these two really devastating young-onset dementias,” she said.

“[This] is critical because sometimes it’s hard to know the difference when we’re just evaluating people at the bedside.”

That distinction matters more than it might seem, because while early-onset Alzheimer’s and FTD share similarities, they differ in key ways.

FTD, for instance, attacks the parts of the brain that control personality and behavior. Early warning signs often include loss of empathy, impulsive decisions, poor judgment and socially inappropriate behavior, along with language difficulties.

These symptoms can appear long before significant memory loss sets in, often leading to misdiagnoses.

Alzheimer’s, on the other hand, typically starts with memory loss, targeting the brain’s hippocampus before spreading and gradually affecting reasoning, judgment and everyday functioning.

The timelines differ, too. FTD tends to move faster, with life expectancy typically between six and eight years after symptoms begin. Early-onset Alzheimer’s patients often live a decade or longer.

“Having a blood test that can help us understand possibly what type of dementia someone has and how quickly it can progress can be a real game changer for patients and their families to understand what is happening or what they’re dealing with,” Sinvani said.

Beyond diagnosis, she added that earlier and more precise detection would also push the healthcare system to strengthen support services for people with early-onset dementia, including psychosocial care, genetic counseling, mental health resources, caregiver groups and advanced care planning.

“That’s what we need to work on now,” Sinvani said.