Can a blood test diagnose cancer?
A blood test alone usually cannot confirm cancer. The National Cancer Institute says that high or low levels of certain substances can be a sign of cancer. So lab tests of blood, urine, and other fluids can help doctors make a diagnosis. But an abnormal result is not a sure sign of cancer.
Lab results for healthy people vary from person to person. Even your own results can vary from day to day. For many tests, you can have a normal result even if you have cancer. You can also have a result outside the normal range even if you are healthy. That is why lab tests alone cannot say for sure if you have cancer or another disease.
Many kinds of blood tests are used in cancer care. They include the complete blood count (CBC), blood chemistry tests, and tumor marker tests. Another is the liquid biopsy, which looks for cancer cells or bits of tumor DNA in the blood.
In most cases, doctors need to do a biopsy to be sure a person has cancer. In a biopsy, they take a sample of abnormal tissue so a pathologist can study it. Your doctor is the best person to explain your lab results and what they mean for you.
Want the full picture? Read our complete explanation: How Cancer Is Diagnosed: Tests and Biopsies
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