When your doctor orders a blood test, he or she chooses from a list of chemical studies to be performed in a laboratory on your blood sample. These lab tests can provide important clues about what's going on inside your body.
If your doctor suspects you may have cancer, he or she may test your blood to:
- Measure the number of red cells, white cells and platelets
- Detect biomarkers that may indicate cancer activity
- Examine various chemicals that can indicate how other parts of your body are functioning, including your liver, kidney, heart and lungs
Read about the following blood tests, below:
- How Are Blood Tests Done?
- Complete Blood Count
- Blood Chemistry
- Blood Smear
- Cytogenetic Analysis
- Flow Cytometry
- Fluorescence in Situ Hybridization (FISH)
- Gene Expression Profiling
- Karyotype Test
- Molecular Profiling
- Next-generation sequencing (NGS)
- Polymerase Chain Reaction (PCR)
- White Cell Differential
How Are Blood Tests Done?
Ask your doctor if you need to follow any special instructions. For example, your doctor may ask you to fast (not eat or drink) before having your blood taken. Blood tests are usually done in one of two ways:
- A needle is inserted into a vein (usually in the fold of your arm) and blood is withdrawn. You may feel a slight pinprick. Your sample is placed in a test tube and sent to a laboratory for analysis.
- If only a small amount of blood is needed, your doctor can obtain blood by simply pricking your finger. Your blood sample is placed on a glass laboratory slide to be examined under a microscope or in a test tube for analysis.
Your blood chemistry is examined using a group of tests called "chemistry panels," which provide information about your general health. Depending on the type of panel, these tests can measure:
- Electrolyte balance (such as sodium or potassium)
- Protein (such as albumin, beta2 -microglobulin, immunoglobulins [IgM, IgG and others] and lactate dehydrogenase [LDH])
- Blood glucose (sugar)
- Chemical substances that indicate liver and kidney function
- Antibodies, including those developed from vaccinations (such as poliovirus antibodies)
- Hormones (such as thyroid hormone)
- Minerals (such as iron, calcium or potassium)
- Vitamins (such as B12 or folate)
How Is It Done? You may be asked to fast before getting the blood test. Once your blood is drawn, it's placed in a tube(s) and usually left to clot. The fluid portion of the blood that remains after clotting, called the serum, is used for various chemical studies.
What Do the Results Mean? The results give your doctor information about your overall health and identify potential problems that may need treatment. Higher levels of certain blood proteins can be signs of disease severity (for example, tumor size and growth rate). High levels of uric acid can sometimes indicate disease as well.
Your doctor may order a blood smear (also called a peripheral blood smear or manual differential) if your CBC results are abnormal or unclear or if he or she thinks a disorder or disease may be disrupting normal blood cell production. This test helps determine whether red cells, white cells and platelets are normal in appearance and number. It's also used to determine the proportion of each type of white cell relative to the total white cell count. The results also help your doctor monitor cell production and cell maturity before and during blood cancer therapy.
How is it done? A single drop of blood is spread on a glass slide, dried and then stained with a special dye. The sample is then examined under the microscope to calculate the number of each type of blood cell. The doctor also compares the size, shape and general appearance of the sampled cells to "normal" cells.
What do the results mean? This test can show the presence of abnormal or immature cells, which may indicate an underlying condition, provide information about its severity and suggest the need for further testing.
Complete Blood Count
A complete blood count (CBC) is a common test that gives a general picture of your health. A CBC measures the number of red cells, white cells (neutrophils, eosinophils, basophils, monocytes and lymphocytes) and platelets and levels of hemoglobin and hematocrit in your blood. Many health conditions cause increases or decreases in blood counts. Your doctor may order a CBC regularly to monitor your condition or track your response to treatment.
How Is It Done? The blood is placed in a test tube containing an anticoagulant (to prevent clotting) and sent to a laboratory to be examined by a pathologist. Dyes are added to the blood sample so that different types of blood cells are noticeable. The slide with the sample of blood cells is examined under a microscope to count the number of cells and see whether they're normal or, if abnormal, the nature of the changes.
What Do the Results Mean? Normal ranges vary slightly among different labs, so ask your doctor to review the results with you. Results above or below normal ranges may signal health problems.
Samples of fluid, tissue and cells are examined under a microscope to look for chromosome changes. Cytogenetic analysis detects chromosome alterations and, in some cases, may identify the actual genes that have been affected. The individual who prepares and examines the chromosomes and interprets the results is called a “cytogeneticist.”
How Is It Done? Cell samples are collected through blood or bone marrow tests.
What Do the Results Mean? The findings help healthcare professionals diagnose specific types of blood cancers, determine treatment approaches and monitor the response to treatment.
Flow cytometry can identify the type of cells in a blood or bone marrow sample, including the types of cancer cells. It detects types of cancer cells based on either the presence or the absence of certain protein markers (antigens) on a cell’s surface. The most common use of flow cytometry is in the identification of markers on cells, particularly in the immune system (called immunophenotyping).
How Is It Done? A sample of cells from the blood or a bone marrow biopsy is treated with special antibodies created in the laboratory. Each antibody only sticks to certain types of cells that have the antigens that fit with it. The cells are then passed through a laser beam. If the cells have the antibodies attached to them, they will give off light that is then measured and analyzed by a computer.
What Do the Results Mean? Flow cytometry can provide information that is used to diagnose, stage and monitor blood cancers. It can also be used to test for minimal residual disease (MRD), the number of cancer cells remaining in the body after treatment. Detecting MRD helps doctors to determine which patients need additional treatment and which patients do not. Evaluating for MRD in your blood may also help your doctor to decide how to monitor your disease and how to follow you after your treatment is complete.
Gene Expression Profiling
A test that can help identify cancer subtypes and risk factors. Gene expression profiling is not generally used in clinical practice and these tests are still mostly used as research tools. This test uses a method called “microarray analysis” to identify combinations of genes that are turned off or on in response to specific conditions.
How Is It Done? Genes are collected from blood or tissue sample.
What Do the Results Mean? The test findings may allow for more accuracy classifying tumors and help doctors to predict how patients will respond to treatment, as well as which patients may be at increased risk for disease relapse.
Immunophenotyping identifies a specific type of cell in a sample of blood, bone marrow or lymph node cells. This procedure can be important in determining the best treatment. For example, immunophenotyping can distinguish myeloid leukemic cells from lymphocytic leukemic cells, normal lymphocytes from leukemic lymphocytes, and B-cell lymphocytes from T-cell lymphocytes. Immunophenotyping also reveals whether your cells are monoclonal (derived from a single malignant cell).
A karyotype test uses a map of the 46 human chromosomes of a cell to identify and evaluate changes to the expected chromosome arrangement, size, shape and number in a sample of blood or bone marrow cells. In some cases, a dye called Giemsa may be used as a stain to make the banding pattern of chromosome pairs easier to see. This is also referred to as "G-banding." The findings can help your doctor develop a more specific treatment plan.
Molecular profiling involves the use of various technologies to understand the underlying characteristics that are found in cancer cells and can be used to identify specific cancer biomarkers that are associated with response, resistance, or lock of response to certain treatment approaches.
First a biopsy procedure obtains a patient's sample from a tumor tissue; bone marrow; lymph node (for some blood cancers); or peripheral blood, in cases when tumor cells are circulating. The sample is then sent to a laboratory, where it undergoes various molecular profiling tests to identify the unique biomarkers that correspond to the patient's cancer. A cancer biomarker is associated with the presence of cancer in the body. A biomarker can be produced by the tumor itself, or it may be a specific response by the body to the presence of cancer.
The ultimate goal of molecular profiling is the development of individualized, highly targeted and effective therapies that can improve patient outcomes.
Types of Molecular Profiling Tests:
Fluorescence in Situ Hybridization (FISH)
Fluorescence in situ hybridization (FISH) is a test performed on your blood or bone marrow cells to detect chromosome changes (cytogenetic analysis) in blood cancer cells. FISH helps identify genetic abnormalities that may not be evident with an examination of cells under a microscope. This helps ensure that you receive the proper treatment. Once treatment begins, doctors use FISH — usually every three to six months — to determine whether a therapy is working.
A laboratory method that uses antibodies to check for certain antigens (markers) in a sample of tissue. The antibodies are usually linked to an enzyme or a fluorescent dye. After the antibodies bind to the antigen in the tissue sample, the enzyme or dye is activated, and the antigen can then be seen under a microscope. Immunohistochemistry is used to help diagnose diseases, such as cancer. It may also be used to help tell the difference between different types of cancer.
Next-generation sequencing (NGS)
The term “next-generation sequencing (NGS)” is a catch-all term used to describe a number of different modern sequencing technologies. These technologies allow for sequencing of DNA and ribonucleic acid (RNA) much more quickly and cheaply than the previously used sequencing methods. Consult your doctor to discuss the possibility of next-generation sequencing as part of your care. Next-generation sequencing is commonly used for patients with cancers that can be treated with a targeted therapy.
In addition, some doctors may recommend next-generation sequencing for patients with advanced cancer that is not responding to standard treatment. This approach may help doctors to identify other treatments that may be effective given the cancer’s genetic makeup.
Polymerase Chain Reaction (PCR)
Polymerase chain reaction (PCR) is an extra-sensitive test that measures the presence of certain biomarkers in blood or bone marrow cells. It measures any remaining blood cancer cells not found by cytogenetic methods such as FISH. PCR is used to diagnose and check a patient's molecular response to treatment. PCR can detect a specific DNA abnormality or marker found in patients with certain blood cancers such as acute promyelocytic leukemia and chronic myeloid leukemia. PCR allows more sensitive follow-up of patients in remission and can help determine whether additional treatment is needed.
To learn more about molecular profiling, download or order the free fact sheet, Cancer Molecular Profiling.
White Cell Differential
A white cell differential (also called a CBC plus differential or a differential) measures the amount of the different kinds of white cells (leukocytes) in the blood. A white cell differential is often included as part of the CBC. This helps determine your body's ability to react to and fight infection. It can also identify various types and stages of blood cancers, detect the existence and severity of infections and measure your response to chemotherapy. The absolute neutrophil count (ANC) is the number of neutrophils (a type of white cell) in the blood that will fight infection.
How Is It Done? After your blood is drawn, it's placed on a stained blood slide and examined. The pathologist determines the percentage of different types of white cells present.
What Do the Results Mean? Abnormal patterns of white cells may point to infections, leukemia, immune disorders, inflammation and other problems.
- Watch videos about lab and imaging tests
- Download or order The Leukemia & Lymphoma Society’s free booklets:
- Cancer Molecular Profiling
- Understanding Genetics
- Understanding Lab and Imaging Tests.