Can a blood test detect cancer?

Lab tests of your blood, urine, and other fluids can help doctors find signs of cancer, because high or low levels of certain substances can be a clue.

But the National Cancer Institute is clear that abnormal lab results are not a sure sign of cancer. For many tests, it is possible to have normal results even if you have cancer, and possible to have results outside the normal range even if you are healthy. That's why lab tests are used together with imaging and biopsies — not on their own.

Some newer blood tests, called liquid biopsies, look for cancer cells or pieces of tumor DNA in the blood. Your doctor is the best person to explain what any result means for you.