Blood Tests

June 12, 2024 

This page was reviewed under our medical and editorial policy by Leslie Popplewell, M.D., hematologist and medical director of Hematology and Blood and Bone Marrow Transplant, City of Hope^® Cancer Center Atlanta

Blood tests are commonly used to help doctors diagnose cancer and understand how the disease is affecting a person’s organs, blood cells, tissues and general health.

Patients may also undergo blood testing to provide doctors with important clues about which treatments to include in their plan, help monitor how these treatments are affecting the cancer and find out if the disease has returned.

Blood Tests for Cancer

Several types of blood tests for cancer may help doctors:

• Find biological markers that may indicate that cancer is present
• Measure levels of white blood cells, platelets and red blood cells to help with disease diagnosis, monitoring and treatment
• Evaluate a variety of chemicals to help gauge factors such as cancer spread and potential damage to organ functioning

These biological markers, chemicals and blood cell counts are also used to develop a cancer treatment plan and to gauge whether certain treatments such as chemotherapy are harming organs or bodily processes.

Does Cancer Show up in Blood Work?

Leukemia is the only cancer that may be directly diagnosed with blood testing, but only when the leukemia cells have moved beyond the bone marrow and into the blood. Even if results from a blood test point to leukemia, additional tests are often used to confirm a leukemia diagnosis.

For most cancers, blood tests are part of a larger diagnostics workup that may also include:

• Biopsy, which is the removal of a tissue sample from the patient’s body for lab analysis (most cancer cases are diagnosed this way)
• Lab tests to analyze urine and other body fluids for cancer markers
• Bone marrow biopsy and aspiration to help understand the cancer subtype and stage or phase
• Imaging tests, such as computed tomography (CT) scans, magnetic resonance imaging (MRI) scans, X-rays, bone scans and ultrasound, to check for tumors and tissue or organ damage

Blood Chemistry Test

Blood chemistry tests, also known as metabolic profiles, help doctors understand how organs and certain bodily processes are working, and how cancer treatments may be affecting the body. Test results provide the levels of different substances that organs and tissues regularly release into the blood, such as:

• Electrolytes
• Proteins, including enzymes
• Sugars
• Fats
• Metabolites

If any of these substances is higher or lower than the normal range, it may indicate cancer or point to certain impacts of cancer treatment. For instance, an abnormal amount of glucose in the blood may indicate pancreatic cancer, and additional testing would be needed for diagnosis.

Some chemotherapy treatments may lower levels of magnesium and potassium, which are electrolytes the body needs for cardiovascular, muscle, nerve, immune, bone and cell health. In such cases, the doctor might change the type of chemotherapy medication prescribed and suggest supplements to help replenish the patient’s electrolytes.

Blood Protein Testing

Blood protein testing has several different names, including protein electrophoresis, serum protein electrophoresis (SPEP), immunofixation electrophoresis (IFE) and serum immunofixation. This testing measures levels of proteins from the two main groups of blood proteins: globulin and albumin. These include the tests listed below.

Albumin: This protein has many important functions in the blood system, including tissue repair and growth. People with myeloma, or plasma cell cancer, may have low levels of this protein.

Alpha-1 globulin: High levels of this protein may be due to infection or inflammation, while low levels may point to liver disease and severe inflammation.

Alpha-2 globulin: High levels of this protein may be due to kidney disease or inflammation, while low levels may point to liver disease and thyroid issues.

Gamma globulin: These proteins include antibodies known as immunoglobulins that help the immune system fight disease and infection. Typically, testing is performed to check levels of three of these immunoglobulins — IgG, IgA and IgM. High levels may indicate certain types of blood, bone marrow and immune system cancer are present in the body, including multiple myeloma, lymphoma, chronic lymphocytic leukemia and Waldenstrom macroglobulinemia.

Beta globulin: This helps fight infection and transports iron throughout the body. High levels may indicate iron deficiency anemia and high cholesterol, while low levels may point to nutritional deficits.

In addition to checking for indicators of certain types of cancers, blood protein testing assists doctors in monitoring patients’ kidney, liver and immune system functioning to help them understand the impacts of cancer and cancer treatments.

Blood Smear

Another common cancer blood test is called a blood smear. For this test, a specialized doctor called a pathologist examines a blood sample under a microscope to analyze the number and appearance of white blood cells, red blood cells and platelets. In addition, the percentage of each type of white blood cell may be counted.

Blood smears may be used to help diagnose leukemia and monitor cancer and its treatments.

Circulating Tumor Cell Test

Compared to other cancer blood tests, the circulating tumor cell test is a more recently developed blood test for cancer. Also known as the liquid biopsy, this test may be used to find and analyze:

• Cancer tumor cells that break off from the main tumor and circulate in the blood, known as circulating tumor cells (CTCs)
• Circulating DNA from the CTCs that is shed as these cells die, known as ctDNA

One benefit of these tests is that they are less invasive than traditional biopsies. They have been used for patients with non-small cell lung, prostate, breast, ovarian, colorectal and other solid tumor cancers to help:

• Find certain cancers in the early stages
• Plan cancer treatment
• Monitor treatment to determine if it is working
• Determine if there is no evidence of a previously treated cancer or if that cancer has returned

Complete Blood Count

A complete blood count (CBC) test measures different components of the blood, including those listed below.

Red blood cell (RBC) count: Red blood cells carry oxygen throughout the body.

Hemoglobin (Hgb): Hgb is the part of each red blood cell that transports iron.

Hematocrit (Hct): Hct is the percentage of RBCs in the blood.

White blood cell (WBC) count: WBCs help the body fight infection. .

WBC differential: The WBC differential counts the number of each type of WBC, including neutrophils, basophils, monocytes, lymphocytes and eosinophils.

Platelet count: Platelets help the blood clot properly.

Mean corpuscular volume (MCV): MCV measures the size of red blood cells.

CBC tests are commonly performed for patients with cancer. Blood count testing results may:

• Give doctors an idea of a patient’s general health
• Assist with diagnosis of cancers such as leukemia and lymphoma
• Evaluate the body’s response to cancer treatment
• Help determine if cancer has reached the bone marrow

Cytogenetic Analysis

The strands that house genes are called chromosomes. Cytogenetic analysis studies pinpoint changes or abnormalities in these chromosomes in a laboratory to help determine if cancer is present. Some of these changes include:

• Parts of a chromosome are lost (deletion)
• Part of a chromosome’s DNA has extra copies (duplication)
• A chromosome is rearranged in reverse order (inversion)
• Part of a chromosome breaks off and attaches to another chromosome (translocation)

This test, sometimes called a karyotype genetic test, may be useful in diagnosing and treating cancers such as leukemia, multiple myeloma and lymphoma.

Flow Cytometry

In flow cytometry, a blood sample is treated with specially created antibodies in a laboratory. These antibodies attach to certain antigens (proteins on cancer cells that trigger an immune response).

This process helps identify which antigens are present and which are missing. This helps identify the types of cancer cells in a patient’s blood, pinpoint the cancer stage, evaluate cancer progression and guide treatment options. It is especially useful for diagnosing different types of lymphoma and leukemia.

Tumor Marker Blood Test

Tumor markers include the presence of certain proteins, as well as gene and cell abnormalities. Normal cells and cancer cells both make tumor markers in response to cancer and noncancerous conditions, but cancer cells make more of them.

There are dozens of different tumor marker tests for all types of blood and solid tumor cancers. Some common tumor marker tests include:

• Prostate-specific antigen (PSA) for prostate cancer
• Human epididymis protein 4 (HE4) and cancer antigen 125 (CA-125) for ovarian cancer
• BCR-ABL gene for leukemia and lymphomas
• Cytokeratin fragment 21-1 for lung cancer
• Bladder tumor antigen (BTA) for kidney, bladder or ureter cancer

Tumor marker tests assist doctors with many facets of cancer care, including diagnosis, staging, choosing and evaluating treatments, determining cancer outcomes and discovering if the cancer has returned.

How to Prepare for a Blood Test

Generally, preparation for a blood test is minimal, unless the patient is asked to fast before the test. If that is the case, the patient should be sure to find out when to stop eating (typically eight to 12 hours before the test) and if medication may be taken during the fast. Keep in mind that habits such as chewing gum or smoking should also be avoided during a fast — only water may be consumed.

However, most blood tests do not require fasting. If a doctor does not tell a patient to fast, the patient should eat normally before the blood test to avoid faulty results.

What Happens During the Blood Test Procedure?

A blood test is a simple procedure in which a medical professional inserts a needle into a patient’s vein to obtain a blood sample for lab analysis. For some people, this may cause nervousness, anxiety and fear. It is OK to tell the person performing the procedure that needles or blood are a source of stress. Some people even bring a family member or friend along for support.

The process of obtaining a blood sample is called phlebotomy, and it is performed by a technician called a phlebotomist, or sometimes by a nurse or doctor. During the procedure:

• The patient may sit or lie down.
• The medical professional taking the sample selects a vein, often in the arm.
• A tight band is placed around the arm or near the site of the vein to help make it more visible.
• Sometimes, the patient is asked to clench his or her fist to further accentuate the vein.
• The phlebotomist, nurse or doctor cleans the skin, inserts the needle into the vein and draws out blood through the attached syringe.
• The tight band is taken off, and the needle is removed from the vein.
• Pressure is applied to the area for a few minutes with a piece of sterile cotton or gauze.
• A bandage may be placed over the site where the needle was inserted.

Sometimes, only a small amount of blood is needed. In this case, the sample is obtained by pricking the patient’s finger.

Typically, blood test procedures only take a few minutes and may be performed at the doctor’s office or an outpatient clinic. Once the procedure is finished, the sample is sent to the laboratory for analysis.

How Long Do Blood Test Results Take?

Some blood test results come back from the lab the same day, while other tests may take a few weeks or more before results are in. Patients may speak with the doctor to find out the typical wait time for their specific blood tests. Be sure to schedule a follow-up appointment with the doctor as well to discuss what the results reveal. 

The care teams at City of Hope^® include world-renowned doctors and scientists who work together to provide patients with advanced blood testing and accurate, timely results. They also provide patients with a comprehensive understanding of their blood test results, and once diagnosed, they work closely with patients to create a personalized cancer treatment plan.