Lab Tests for Cancer
How is cancer diagnosed?
The complete evaluation for suspected cancer usually requires a complete health history and physical exam along with diagnostic testing. Many tests may be needed to figure out if you have cancer, or if another condition (such as an infection or inflammation) is mimicking the symptoms of cancer. The healthcare provider forms a list of possible diagnoses that can explain the symptoms and complaints. Then the provider 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, watch the disease process, and plan for and evaluate the effectiveness of treatment. In some cases, repeat testing is needed when a person’s condition has changed, to monitor treatment or condition. Repeat testing may also be needed if a sample collected was not of good quality, or to confirm an abnormal test result. Diagnostic procedures for cancer may include imaging, lab tests (including tests for tumor markers), tumor biopsy, endoscopic exam, surgery, or genetic testing. The most common way a cancer is diagnosed is with a tissue or needle biopsy, not a blood or urine test.
What are the different types of lab tests?
Clinical lab testing uses chemical processes to measure levels of chemical components in body fluids and tissues. The most common samples used in clinical lab tests are blood and urine samples. Many different tests exist to find and measure almost any type of chemical component in blood or urine. Components may include blood glucose, electrolytes, enzymes, hormones, fats (lipids), other metabolic substances, and proteins. Below are descriptions of some common lab tests.
A variety of blood tests are used to check the levels of substances in the blood that show how healthy the body is and if infection is present. For example, blood tests show high (elevated) levels of waste products, such as creatinine or blood urea nitrogen. This means that the kidneys are not working efficiently to filter those substances out. Other tests check for the presence of electrolytes. These are chemical compounds, such as sodium and potassium, that are vital 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. Red blood cells are important for carrying oxygen and fighting anemia and fatigue. The hemoglobin part of the CBC measures the oxygen-carrying capacity of the red blood cells. The hematocrit part measures the percentage of red blood cells in the blood. White blood cells fight infection. Increased numbers of white blood cells may mean there is an infection. Platelets prevent the body from bleeding and bruising easily. A CBC may be done to help diagnose certain blood cancers such as leukemia.
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 noncancer or benign condition. But it can also mean there is 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 person 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. New tumor markers are constantly being introduced.
Tumor markers are useful in identifying possible problems or following treatment. But in most cases they must be used along with other tests for the following reasons:
Cells other than cancer cells also produce tumor markers. People with noncancer conditions may also have high 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 cancerous (malignant), it stops producing tumor markers. This makes it seem that the tumor has shrunk.
The following is a brief description of some of the more useful tumor markers:
Prostate-specific antigen (PSA). PSA is always present in low concentrations in the blood of adult males. An elevated PSA level in the blood may indicate prostate cancer. But other conditions, such as benign prostatic hyperplasia and prostatitis, can also raise PSA levels. The speed over time of the rise in PSA, is particularly useful. PSA levels are used to evaluate how a person has responded to treatment and to check for cancer recurrence.
CA 125. Ovarian cancer is the most common cause of elevated CA 125. But cancers of the uterus, cervix, pancreas, liver, breast, lung, and digestive tract can also raise CA 125 levels. Several noncancer conditions can also elevate CA 125. CA 125 is used mainly to monitor the treatment of ovarian cancer.
Carcinoembryonic antigen (CEA). CEA is normally found in small amounts in the blood. Colorectal cancer is the most common cancer that raises this tumor marker. Several other cancers can also raise levels of carcinoembryonic antigen.
Alpha-fetoprotein (AFP). AFP is normally elevated in pregnant women since it is produced by the fetus. But AFP is not often found in the blood of adults. In men, and in women who are not pregnant, a high level of AFP may indicate liver cancer or cancer of the ovary or testicle. Noncancer conditions may also cause somewhat elevated AFP levels.
Human chorionic gonadotropin (HCG). HCG is another substance that appears normally in pregnancy and is produced by the placenta. If pregnancy is ruled out, HCG may indicate cancer in the testis, ovary, liver, stomach, pancreas, and lung. Marijuana use can also raise HCG levels.
CA 19-9. This marker is linked to cancers in the colon, stomach, and bile duct. High levels of CA 19-9 may indicate advanced cancer in the pancreas. But it is also linked to noncancer conditions, including gallstones, pancreatitis, cirrhosis of the liver, and cholecystitis.
CA 15-3. This marker is most useful in evaluating the effect of treatment for women with advanced breast cancer. Elevated levels of CA 15-3 are also linked to cancers of the ovary, lung, and prostate. They are also linked to noncancer conditions such as benign breast or ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis. Pregnancy and lactation also can raise CA 15-3 levels.
CA 27-29. This marker, like CA 15-3, is used to follow the course of treatment in women with advanced breast cancer. Cancers of the colon, stomach, kidney, lung, ovary, pancreas, uterus, and liver may also raise CA 27-29 levels. Noncancerous conditions associated with this substance are first trimester pregnancy, endometriosis, ovarian cysts, benign breast disease, kidney disease, and liver disease.
Lactate dehydrogenase (LDH). LDH is a protein that normally appears all over the body in small amounts. Many cancers can raise LDH levels. So it is not useful in identifying a specific kind of cancer. But measuring LDH levels can be helpful in monitoring treatment for cancer. Noncancer conditions that can raise LDH levels include heart failure, hypothyroidism, anemia, and lung or liver disease.
Neuron-specific enolase (NSE). NSE is linked to several cancers. But it is used most often to monitor treatment in people with neuroblastoma or small cell lung cancer.