Blood tests are a common part of medical evaluations, often raising questions about their ability to detect cancer. While offering valuable health insights, they are not definitive standalone diagnostic tools. A comprehensive evaluation involves multiple methods, with blood tests serving as one piece of the overall picture.
What Blood Tests Look For
Blood tests identify cancer-signaling substances or markers. Tumor markers, produced by cancer cells or the body’s response, include Prostate-Specific Antigen (PSA) for prostate, Cancer Antigen 125 (CA-125) for ovarian, Carcinoembryonic Antigen (CEA) for colorectal, and Alpha-fetoprotein (AFP) for liver or germ cell tumors.
A newer approach detects circulating tumor DNA (ctDNA), or “liquid biopsy.” This identifies small fragments of cancer DNA in the bloodstream, valuable for detection and monitoring.
Routine complete blood count (CBC) tests reveal abnormalities. Unusual cell numbers might suggest blood cancers like leukemia or lymphoma. A CBC can also indicate cancer-related issues like anemia, occurring due to the disease or its treatments.
Other blood chemistry tests assess electrolytes, proteins, sugars, and enzymes. Abnormal results can point to organ function issues affected by cancer or its treatments.
How Blood Tests Are Used in Cancer Management
Blood tests play a multifaceted role in cancer care, including screening high-risk individuals. For example, the PSA test screens for prostate cancer, though its general use is debated.
After a cancer diagnosis, blood tests monitor treatment effectiveness. Tracking tumor marker levels helps doctors determine if therapies work, with decreasing levels indicating a positive response, allowing for timely adjustments.
Blood tests also detect potential cancer recurrence after treatment. Regular marker monitoring provides early warning if cancer returns, allowing for prompt intervention and ongoing surveillance.
Beyond cancer-specific markers, routine blood tests assess overall health and organ function during cancer treatment. They ensure organs function well and monitor for potential side effects.
Limitations of Blood Tests for Cancer Diagnosis
Blood tests are valuable but rarely definitive for cancer diagnosis alone. A significant limitation is false positives, where elevated markers stem from non-cancerous conditions like inflammation, benign tumors, or infections, mimicking cancer.
Conversely, false negatives can occur if a blood test doesn’t detect cancer. Some cancers don’t produce detectable markers, or levels might be too low, especially in early stages. Thus, a “normal” result doesn’t guarantee cancer’s absence.
Most tumor markers lack specificity, not being exclusive to a single cancer type. This broad reactivity necessitates further investigation to pinpoint the exact cause of an elevation.
Blood tests cannot pinpoint a tumor’s exact location or advancement. They provide systemic information, but detailed anatomical and staging requires imaging scans. A positive result always necessitates additional diagnostic procedures.
For a definitive cancer diagnosis, a biopsy is required. Blood tests serve as indicators that prompt further, more invasive, and conclusive testing.
What Happens After an Abnormal Blood Test
An abnormal blood test suggesting cancer initiates follow-up steps. The healthcare provider will order additional, more specific tests, including repeat blood tests or different types that delve deeper into specific markers or cell characteristics.
Imaging scans (e.g., X-rays, CT, MRI, PET) visualize internal organs and identify suspicious masses. These scans help locate potential tumors and assess their size and spread. Endoscopic procedures, using a thin, flexible tube with a camera, may examine internal tissues directly.
The most definitive step in diagnosing cancer is a biopsy. During this procedure, a small tissue sample is taken from the suspicious area and examined under a microscope by a pathologist. This microscopic analysis is crucial for confirming cancer cells and determining their specific type and characteristics.
Following these investigations, the patient may be referred to specialists for further evaluation. An abnormal blood test result does not automatically confirm cancer; further investigation is necessary for an accurate diagnosis and appropriate action.