Blood tests alone do not definitively diagnose cancer. Instead, they offer important clues and are used with other diagnostic methods. No single blood test can detect all types of cancer. Blood work provides valuable information, often used with other diagnostic methods to confirm a diagnosis.
How Blood Tests Provide Clues
Routine blood tests can reveal abnormalities suggesting cancer. The Complete Blood Count (CBC) measures red blood cells, white blood cells, and platelets. Deviations prompt further investigation. For instance, low red blood cell count (anemia) can associate with cancers affecting blood production or causing chronic bleeding.
Abnormal white blood cell counts, high or low, might signal blood cancers like leukemia or lymphoma. Platelet count issues can also point to bone marrow disorders or other cancers. Beyond CBC, liver function tests (LFTs) or kidney function tests (KFTs) can show organ dysfunction. Abnormal levels in these tests could indicate cancer affecting organ performance.
Key Blood Markers for Cancer
Specific blood tests measure tumor markers, substances produced by cancer cells or the body in response to cancer. These markers can be elevated with certain cancers. Their elevation does not confirm cancer, as non-cancerous conditions can also cause increases.
Examples include prostate-specific antigen (PSA) for prostate cancer, which can also be high due to benign prostatic hyperplasia or inflammation. CA-125 is often elevated in ovarian cancer, but levels can also rise due to non-cancerous conditions like endometriosis or pelvic inflammatory disease.
Carcinoembryonic antigen (CEA) may be increased in colorectal, breast, lung, and pancreatic cancers. Tumor markers are useful but are used with other diagnostic methods, not as standalone tests.
Understanding Test Limitations
Blood tests for cancer have limitations, including false positives. Elevated marker levels can occur without cancer due to non-cancerous conditions like inflammation, benign tumors, or certain medications. For instance, high PSA can result from non-cancerous prostate enlargement, and elevated CA-125 from menstrual periods or ovarian cysts.
Conversely, false negatives can occur when cancer is present but blood markers appear normal. Not all cancers produce detectable marker levels, and many early-stage cancers may not produce sufficient amounts. Even with established markers, some individuals may not show elevated levels. Blood tests serve as indicators warranting further investigation, not definitive diagnostic tools.
Integrating Blood Tests into Diagnosis
Blood tests are one component of a comprehensive cancer diagnosis. Healthcare providers combine blood test results with other diagnostic tools. Physical examinations are often the first step. Imaging scans (X-rays, CT, MRI, PET) provide detailed images to identify tumors or abnormalities.
A biopsy remains the definitive method for diagnosing most cancers. This involves removing a tissue sample for microscopic examination to confirm cancer cells and determine the specific type. Blood tests also monitor diagnosed patients, assessing treatment effectiveness or detecting recurrence after therapy.