Lab Tests for Cancer
How is cancer diagnosed?
There is no single test that can accurately diagnose cancer. The complete evaluation
for suspected cancer usually requires a thorough history and physical exam along with
diagnostic testing. Many tests may be needed to determine whether a person has cancer,
or if another condition (such as an infection or inflammation) is mimicking the symptoms
of cancer. The doctor 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,
to monitor treatment or condition, 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.
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 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. 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
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, 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. A CBC may
be done to help diagnose certain blood cancers such as leukemia and lymphoma, or to
help determine how the body is handling the cancer treatment.
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
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 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 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.
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 velocity,
or rapidity over time of the rise in PSA, is particularly useful. PSA levels are used to evaluate how a
patient 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 noncancerous conditions can also elevate CA 125. CA 125 is used primarily
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. However,
AFP is not usually found in the blood of adults. In men, and in women who are not
pregnant, an elevated level of AFP may indicate liver cancer or cancer of the ovary
or testicle. Noncancerous 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 associated with cancers in the colon, stomach, and bile duct. Elevated
levels of CA 19-9 may indicate advanced cancer in the pancreas, but it is also associated
with noncancerous 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 associated with cancers of the
ovary, lung, and prostate, as well as noncancerous 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 throughout the body in small amounts. Many
cancers can raise LDH levels, so it is not useful in identifying a specific kind of
cancer. Measuring LDH levels can, however,be helpful in monitoring treatment for cancer.
Noncancerous conditions that can raise LDH levels include heart failure, hypothyroidism,
anemia, and lung or liver disease.
Neuron-specific enolase (NSE). NSE is associated with several cancers, but it is used most often to monitor treatment
in patients with neuroblastoma or small cell lung cancer.