Blood tests are a common part of routine health check-ups. While they can offer valuable clues and indicate potential abnormalities, they are generally not used for a definitive cancer diagnosis on their own. Instead, they serve as one piece of a larger diagnostic puzzle.
What Blood Tests Can Reveal
A complete blood count (CBC) is a general blood test that measures the different cells in your blood, including red blood cells, white blood cells, and platelets. Abnormalities in these counts can sometimes suggest the presence of cancer. For instance, a low red blood cell count, also known as anemia, might be caused by prolonged bleeding or certain cancers like leukemia or lymphoma. Similarly, an unusually high or low white blood cell count can indicate infections, bone marrow disorders, or blood cancers such as leukemia or myelodysplastic syndrome. An abnormal platelet count, either too high or too low, has also been linked to certain cancers and bone marrow issues.
Beyond general blood tests, specific tumor markers can provide additional insights. Tumor markers are substances, often proteins, produced by cancer cells or by the body in response to cancer. These markers can be found in blood, urine, or other bodily fluids. Examples include Prostate-Specific Antigen (PSA) for prostate cancer, Carcinoembryonic Antigen (CEA) for colorectal cancer, and Cancer Antigen 125 (CA-125) for ovarian cancer. Elevated levels of these markers can suggest the presence of cancer, help monitor treatment effectiveness, or detect recurrence.
Why Blood Tests Aren’t Definitive
Many abnormalities found in a complete blood count are non-specific and can be caused by various non-cancerous conditions. For example, a high white blood cell count might indicate an infection or inflammation rather than cancer. Anemia can result from nutritional deficiencies or other chronic diseases, not just cancer.
Tumor markers also have limitations, as their levels can be elevated due to benign conditions. For instance, PSA levels can rise due to an enlarged prostate, and CA-125 levels can increase during menstruation, pregnancy, or with conditions like endometriosis. This non-specificity can lead to false positive results, where a test suggests cancer when none is present, causing unnecessary anxiety and further testing. Conversely, false negative results can occur, meaning a blood test appears normal even when cancer is present, especially in early stages. This is because not all cancers produce detectable markers, or the levels might not be elevated enough to register as abnormal.
The Role of Further Diagnostics
When blood test results show abnormalities or when cancer is otherwise suspected, further diagnostic procedures are necessary to establish a definitive diagnosis. A comprehensive evaluation usually involves a combination of tests, starting with a thorough medical history and physical examination.
Imaging scans are commonly used to visualize internal organs and structures. These include X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI), and positron emission tomography (PET) scans. These scans can help locate tumors, determine their size, and assess if cancer has spread. However, imaging tests cannot definitively confirm cancer; they can only show suspicious areas.
The gold standard for cancer diagnosis is a biopsy, where a small sample of suspicious tissue is removed and examined under a microscope by a pathologist. Endoscopies, which involve inserting a thin, flexible tube with a camera to examine internal organs, may also be performed. It is important to consult a healthcare professional for proper interpretation of any test results and guidance on the appropriate next steps.