Blood courses through your body with every heartbeat. It carries life-giving oxygen to every organ. Blood also helps remove the waste products your body makes. Because it flows to and from every part of the body, blood can provide an important window into what’s happening under the skin.
“So many biochemical compounds get absorbed from the tissues of the body into the blood. This makes the blood a really good place to look for hints of disease,” says Dr. Lori Minasian, who helps oversee cancer prevention research at NIH.
Blood tests can help your health care provider diagnose diseases. They can also help them choose the best treatments for many health conditions. Commonly used blood tests look for compounds that signal an increased risk of heart disease. Other tests help diagnose diabetes, vitamin deficiencies, and many types of infections.
Blood tests have been helpful for preventing some common, dangerous health events, like heart attack and stroke. NIH-funded researchers are working to expand the number of health conditions that can be detected with a simple blood test. These include cancer, dementia, and other deadly diseases.
Tracking Cancer
Like normal cells in the body, cancer cells also come into regular contact with blood. This means that substances from tumors, like pieces of genes or even whole cancer cells, can get into the bloodstream.
Researchers have developed tests to look for such substances in the blood. These are called liquid biopsies. These tests are already used for some types of cancer to monitor whether a tumor comes back after treatment, Minasian says. Scientists are also looking at whether these tests can identify which tumors may need more aggressive treatment to prevent them from returning.
Blood tests might one day be used for cancer screening, too. Screening tests aim to catch cancer early—before symptoms develop. Cancers found early are often easier to treat. This can save lives.
Some cancer screening tests are already available through your doctor. These include mammograms for breast cancer and colonoscopy for colorectal cancer. But neither are as simple to do as a blood test.
Many types of cancer still don’t have screening tests available. More than half of cancer deaths are from cancers that don’t have screening tests yet. These include deadly cancers like ovarian cancer and pancreatic cancer.
“The idea that, with a single blood test, you could screen for many deadly cancer types, has huge potential,” says Minasian.
The usefulness of blood tests for cancer screening is still in the early research stages. Right now, there’s limited evidence for any benefits. Despite this, blood tests for cancer screening are marketed directly to consumers. People should be very careful about using these tests right now, Minasian cautions.
“There is not enough data to understand the full risks and benefits of using these blood tests for cancer screening,” she says. “The results could lead to anxiety or may provide a sense of false reassurance.”
If you’re concerned about your cancer risk, talk with a health care provider. They can help you stay up to date with proven screening tests.
Detecting Alzheimer’s Disease
Like your body, your brain is full of blood vessels. So substances from injured brain cells can also enter your blood.
For decades, researchers have been trying to develop blood tests to help diagnose and better treat mental health conditions, explains Dr. John Hsiao, a psychiatrist at NIH. But, this has proven difficult.
Blood tests to determine whether someone is at risk for dementias are showing promise, Hsiao says. The proteins that damage brain cells in these conditions are now well understood. This means they can be measured.
The most common cause of dementia in older adults is Alzheimer’s disease. Measuring Alzheimer’s disease proteins currently requires a brain scan or collecting spinal fluid. These tests can be costly and aren’t available in every community.
“But these abnormal proteins that build up in the brain also show up in the blood,” says Dr. Reisa Sperling, a neurologist at Harvard Medical School. Blood tests for Alzheimer’s have the potential to be “cheap and easy,” Hsiao adds.
Recent studies have shown that blood tests can detect early signs of Alzheimer’s disease in the brain. So researchers are looking at whether they can use them to find and treat people with the disease early. They hope this could help prevent or slow the loss of brain cells.
“Studies so far suggest that our best chance at being able to delay the memory loss and other symptoms of Alzheimer’s disease would be to treat very early,” Sperling says. But she does not recommend people without symptoms get blood tests done outside of studies just yet.
Some blood tests that claim to detect Alzheimer’s disease are being advertised to the public. But they are not yet FDA approved. Sperling warns that some of these tests may not be as accurate as those being used by researchers.
If you’re concerned about your risk for dementia, Sperling recommends joining a clinical study. “There are great research trials for people to go into, and they will use the best blood tests available,” she says. Learn more at Alzheimer's Disease Research Centers or Alzheimer's Clinical Trials Consortium(link is external).
Researchers are also trying to develop blood tests to detect other causes of dementia and brain conditions like Parkinson’s disease. “These tests have the potential to really change how we diagnose and understand these conditions,” Hsiao says.
Stay Up To Date
It may be a while before a blood draw at your local clinic can find diseases like cancer or dementia. But keeping up with current blood tests can help you get early treatment for other potentially life-threatening problems.