Along with the hiss of a blood-pressure cuff and sticking out your tongue, the needle stick of a blood draw is a familiar part of a doctor visit. And for good reason: a vial of blood can give your physician a real-time look at how much cholesterol you have circulating in your blood vessels, for instance, or which vitamins and hormones you have in good or not-so-good supply. But now it turns out that that’s just a sliver of the volumes of medical information hidden in human blood. Researchers are discovering that each of us walks around with 1.5 gal. (5.7 L) of what may be the most sophisticated and revealing diagnostic available. Each drop teems with data, not just about your current state of health but also about what your future might hold.
The breadth of blood-detectable conditions is exploding thanks to the latest technologies. As doctors get better at understanding what goes wrong at the molecular level when we get sick, they can better pick out specific compounds in human plasma—the component that holds all the blood cells—that signal the first stages of trouble.
“There’s a data set in blood that is 10 times—even 100 times—more interesting than that in the genome,” says Dr. Eugene Chan, CEO and founder of DNA Medicine Institute, a biomedical product-development company that is creating a one-drop-tells-all blood test that will scan for everything from Alzheimer’s to multiple sclerosis and cancer.
Chan’s work is part of an effort that is under way by scientists and entrepreneurs across the country to tap blood’s huge potential for indicating what illnesses may be lurking in the body. In the near future, Chan thinks, a blood test may be able to detect early breast cancer more reliably than a mammogram; it might even alert doctors to the first signs of Alzheimer’s, making it possible to intervene before toxic changes ravage the brain.
Success will mean a transformation in medicine as blood tests reveal things that have until now required invasive surgery or radiation imaging. Blood’s advantages are obvious: it’s easy to access, it’s inexpensive to test, and nearly every doctor’s office or clinic can draw a tube of it. It’s no surprise that the market for immediate-gratification diagnostic tests, including blood-based ones, could grow by nearly 10% each year, to reach an estimated $27.5 billion by 2018. Health care entrepreneurs are jumping on the bandwagon, developing commercial tests that promise—with limited proof so far—a tell-all diagnostic blood scan.
There are challenges to overcome before that payoff. The same qualities that make blood’s information so promising also make it challenging to exploit. It’s a case of almost too much information. Teasing out specific markers for illness—let alone interpreting them with any accuracy—is a tedious and, until recently, nearly impossible task.
But a growing database of the molecular fingerprints of diseases’ proteins, enzymes and other compounds is making it easier to sort the more significant data from less useful information. In June, researchers at Brigham and Women’s Hospital announced that they had found a way to detect thousands of viruses—and every viral infection a person had—from a drop of blood in just seconds.
“It’s both the best fluid to work with and also one of the more complicated ones to study,” says Dr. Robert Siman, professor of neurosurgery at the University of Pennsylvania. Which means the big questions now are: How quickly can science unlock the secrets of our blood? And once that happens, what’s the best way to make use of everything those tests can tell us?
Cancer testing is providing some of the most enticing hope for decoding blood. As it stands, detecting cancerous tumors relies on rather crude methods—people are supposed to literally feel or look for lumps or lesions in the case of breast and skin cancers, for example. By the time the cancer is visible or detectable to the touch, the disease is often far along and harder to treat.
Scans, meanwhile, can pick up smaller growths, but they require regular follow-ups and aren’t completely reliable either. A spate of new studies about mammography found that women who undergo routine screening are not less likely to die of the disease than those who forgo the scans. And though the most common kind of prostate-cancer test already relies on a blood sample, this older technology measures levels of a protein that often rise when either tumors or benign growths take hold in the organ—so it is not sophisticated enough to pick out markers for aggressive cancers from the kind that don’t require treatment.
New blood tests, in contrast, would function more as a liquid biopsy. One approach is to home in on genetic fragments that are overactive in tumor cells and shed into the blood, and connect them to molecules of silver, similar to the way that images in a photograph are developed. Doctors would then be alerted to the presence of malignant cells. In the case of prostate cancer, only the genetic signatures associated with aggressive, need-to-treat tumors would be flagged.
Sounds simple, but in practice, it’s incredibly intricate. Cancer cells arise from normal cells that have developed mutations, so these aberrant snippets of tumor DNA aren’t easy to distinguish from normal genetic material. “You’re looking for a needle in a haystack,” says Dr. Max Diehn, a radiation oncologist at Stanford University who is mining blood for early signs of lung cancer.
These strategies also depend on knowing what you’re looking for. And that is where blood testing can benefit from an explosion of research that’s uncovering both gene- and protein-based markers linked to diseases that go beyond cancer.
At Stanford, researchers have narrowed down Alzheimer’s markers to a half-dozen blood proteins that signal a buildup of the disease’s hallmark amyloid plaques in the brain, while at the University of California, Los Angeles, Dr. Liana Apostolova is developing a similar test. “This blood test is less invasive than a lumbar puncture to study spinal fluid. And it doesn’t have radiation like PET scans, which are the only other ways to look for the disease,” she says.
There are currently no therapies to halt the gradual decline in cognitive functions from Alzheimer’s, but knowing that the disease has taken hold can help patients plan for when they will be more debilitated by the condition, Apostolova says. It’s also important to be ready with a reliable and sensitive blood test for when treatment breakthroughs do occur, since blood can be a useful way to monitor how well patients respond to those therapies.
Blood testing holds similar potential for people with rheumatoid arthritis (RA), an immune-triggered disorder that causes painful inflammation in the joints and can severely restrict movement. Traditional blood tests for inflammation—a hallmark characteristic of RA and other autoimmune diseases—aren’t especially helpful, since inflammatory markers can also be a sign that the patient has a cold or some other condition the immune system is fighting.
Scientists at Crescendo Bioscience, a San Francisco company developing a number of blood-based diagnostics for such diseases, have developed a test that looks at a dozen blood markers for RA and can rank patients’ inflammation as mild, moderate or severe. This is critical because treating early inflammation is key to preserving joints and preventing more serious damage, which can result in disability and a lifelong reliance on side-effect-heavy prescription drugs or multiple surgeries or both.
Brain Trauma is another promising area of research. Researchers foresee a day when an athletic coach could assess a player’s head injury in real time. Team doctors could draw blood to determine if it’s safe for the player to get back in the game. Experts are looking at total tau and SNTF, for example—two proteins that tend to spike in the hour or so after a concussion. Studies show that peak levels of total tau correlate with how many days the person experiences symptoms such as dizziness, nausea and memory problems. And SNTF may be a good barometer for serious structural damage to the brain. It was tested in a small number of head-injury patients at Houston hospitals in 2013. Compared with a healthy group of controls, the patients who had elevated SNTF had cognitive issues that persisted for months after the blow.
About 20% of patients with brain injuries experience continual deficits in thinking and other functions. If blood tests can help identify this minority, it could mean the difference between early treatment and serious problems that develop and worsen over time.
All of this begs the question: How much do you really want to know? This is something patients will soon confront as they are offered the option of knowing their future risk of cancer, Alzheimer’s or other conditions. For some it may be welcome information, while for others it may bring only uncertainty and anxiety.
Most researchers say the prospects for better care make the growth of blood testing both inevitable and worthwhile. It isn’t just the benefit to individual patients. If a blood test can help reveal whether a drug is working, for instance, it can lead to more effective care for everyone. “We can start to understand why some patients don’t respond to conventional treatments,” says Dr. Chad Mirkin, a professor of chemistry at Northwestern University who developed the so-called liquid biopsy that lights up when cancer cells are present.
There’s no question our blood has a lot to tell us about our health—we just have to get better at reading what it has to say.
This appears in the July 27, 2015 issue of TIME.