There are numerous serious diseases that a blood test can detect.
Sometimes a blood test will only detect a disease marker, but others will outright reveal presence of the medical condition.
For example, there are blood tests that detect markers for cancer, but these are not diagnostic. They serve to guide a doctor in the next steps.
These include the PSA test for prostate cancer and the CA-125 test for ovarian cancer.
One interesting blood test is called the D-dimer. It’s given to people who present with symptoms suspicious for a pulmonary embolism (a blood clot that has traveled to the lungs).
However, a positive D-dimer result doesn’t always mean a blood clot. The result is often positive in elderly people simply because they are old.
The younger a person is who has a positive D-dimer, the more likely it WILL mean a blood clot somewhere in the body.
“Blood tests can be done for a variety of reasons,” says Walter Gaman, MD, FABFM, board certified in family medicine and the author of several award-winning books including “Age to Perfection: How to Thrive to 100, Happy, Healthy, and Wise.”
“They can shed a good amount of information about a person’s health or disease state, but they are not always definitive.
“For example, a complete blood count may reveal that a patient’s white count is elevated, a sign of infection, but it does not tell the doctor what type of infection.
“On the contrary, a blood test that is more specific, like tests for hepatitis, may tell the doctor if the patient has been exposed previous or if they have a current infection.
Blood tests are often given when the following conditions are suspected:
• Celiac disease
• Heart attack (though other conditions can cause elevated troponin such as rhabdomyalysis, but in patients presenting to the ER with chest pain, shortness of breath, nausea, sweating, etc., the troponin test is used to diagnose or rule out heart attack.)
• Genetic disorders (e.g., Angelman syndrome, Prader-Willi syndrome, Down syndrome)
• Liver disease
• Pancreatic disease
• Systemic infection
• Thyroid disorder
What about prediabetes and diabetes?
“Sometimes, blood tests reveal a small amount of information or a sign that something may be wrong, but don’t give the bigger picture or enough for diagnosis,” says Dr. Gaman.
“This is often seen in a glucose or blood sugar level. The blood sugar may be elevated, but it is a test designed to only look at the level at that given time.
“The doctor will then order another test, usually a hemoglobin A1C to see the trend of blood sugar over the period of three months.
“Depending on the results, the patient may have no risk of diabetes, prediabetes or be fully diabetic.”
Just how many blood tests for disease exist?
“There are hundreds, if not thousands, of blood tests,” says Dr. Gaman. “Most patients assume that if a doctor has taken blood and everything is fine, they are completely healthy.
“This is a common misconception. The blood is collected with certain tests in mind. Blood is not ‘routinely’ tested for more than the basics.
“The basics usually include blood count and chemistry panels that look at glucose, liver enzymes and electrolytes.
“Things like HIV, cancer markers, heart disease or other tests may not be checked unless specifically requested.
“It’s best to communicate with your healthcare provider and ask questions about what tests were ordered and why.”
Blood Test for Concussion Is Very Accurate
Though not 100 percent definitive, the Banyan brain trauma indictor blood test in February 2018 was approved by the FDA.
This measures proteins that are released from an injured brain within 12 hours of trauma.
It’s 97.5 percent accurate for detecting concussions and 99.6 percent accurate for ruling out concussions.
Dr. Gaman is with Executive Medicine of Texas and is with the Staying Young Radio Show 2.0 podcast.
Lorra Garrick has been covering medical, fitness and cybersecurity topics for many years, having written thousands of articles for print magazines and websites, including as a ghostwriter. She’s also a former ACE-certified personal trainer.