How is cancer diagnosed?
There is no single test that can accurately diagnose cancer. The complete evaluation of a patient usually requires a thorough history and physical examination along with diagnostic testing. Many tests are needed to determine whether a person has cancer, or if another condition (such as an infection) is mimicking the symptoms of cancer. The physician forms a list of possible diagnoses that can explain the symptoms and complaints, and then orders testing to confirm a diagnosis and/or to exclude other potential diagnoses. Effective diagnostic testing is used to confirm or eliminate the presence of disease, monitor the disease process, and plan for and evaluate the effectiveness of treatment. In some cases, it is necessary to repeat testing when a person’s condition has changed, if a sample collected was not of good quality, or an abnormal test result needs to be confirmed. Diagnostic procedures for cancer may include imaging, laboratory tests (including tests for tumor markers), tumor biopsy, endoscopic examination, surgery, or genetic testing.
What are the different types of laboratory tests?
Clinical lab testing uses chemical processes to measure levels of chemical components in body fluids and tissues. The most common specimens used in clinical lab tests are blood and urine. Many different tests exist to detect and measure almost any type of chemical component in blood or urine. Components may include blood glucose, electrolytes, enzymes, hormones, lipids (fats), other metabolic substances, and proteins. The following are some of the more common laboratory tests:
A variety of blood tests are used to check the levels of substances in the blood that indicate how healthy the body is and whether infection is present. For example, blood tests revealing elevated levels of waste products, such as creatinine or blood urea nitrogen (BUN), indicate that the kidneys are not working efficiently to filter those substances out. Other tests check the presence of electrolytes -- chemical compounds such as sodium and potassium that are critical to the body's healthy functioning. Coagulation studies determine how quickly the blood clots.
A complete blood count (CBC) measures the size, number, and maturity of the different blood cells in a specific volume of blood. This is one of the most common tests performed. Red blood cells are important for carrying oxygen and fighting anemia and fatigue; the hemoglobin portion of the CBC measures the oxygen-carrying capacity of the red blood cells, while the hematocrit measures the percentage of red blood cells in the blood. White blood cells fight infection. Increased numbers of white blood cells, therefore, may indicate the presence of an infection. Platelets prevent the body from bleeding and bruising easily.
Urinalysis breaks down the components of urine to check for the presence of drugs, blood, protein, and other substances. Blood in the urine (hematuria) may be the result of a benign (noncancerous) condition, but it can also indicate an infection or other problem. High levels of protein in the urine (proteinuria) may indicate a kidney or cardiovascular problem.
Tumor markers are substances either released by cancer cells into the blood or urine, or substances created by the body in response to cancer cells. Tumor markers are used to evaluate how well a patient has responded to treatment and to check for tumor recurrence. Research is currently being conducted on the role of tumor markers in detection, diagnosis, and treatment of cancers, and new tumor markers are continuously being introduced.
Tumor markers are useful in identifying potential problems, but in most cases they must be used along with other tests for the following reasons:
People with benign conditions may also have elevated levels of these substances in their blood.
Not every person with cancer has tumor markers.
Some tumor markers are not specific to any one type of cancer.
Sometimes, as the cancer becomes more malignant, it stops producing tumor markers, making it appear that the tumor has shrunk.