What is a CBC blood test
A CBC (complete blood count) is a common blood test that measures and evaluates the different types of cells in the blood. While it is often part of a routine health checkup, it is also one of the first tests commonly used to detect signs of many types of blood cancer.
A CBC is usually done at a lab or point of care setting. You may need to follow special instructions beforehand, such as stopping certain medications that can affect results. During the test, blood is drawn from a vein in your arm using a needle. The blood is collected in a labeled tube and sent to a lab, where a technologist uses specialized equipment to examines you blood cell counts.
| Component | Typical Normal Range | Function/Notes |
|---|---|---|
| White Blood Cells (WBCs) | 4,200 – 10,000 cells per microliter | Fight infection and support immune function |
| Red Blood Cells (RBCs) |
Females: 3.8 – 5.4 million cells per microliter Males: 4.3 – 6.3 million cells per microliter |
Carry oxygen throughout the body |
| Hemoglobin (Hb) |
Females: 12.0 – 16.0 grams per deciliter Males: 14.0 – 18.0 grams per deciliter |
Protein in RBCs that carries oxygen |
| Hematocrit (Hct) |
Females: 37% – 47% Males: 41% – 51% |
Percentage of blood made up of red blood cells |
| Platelets | 150,000 – 450,000 per microliter | Help with blood clotting to prevent bleeding |
The ABCs of CBCs
Think of a CBC like a quick snapshot of your blood—sometimes it can feel like reading an alphabet soup of medical abbreviations.
Key parts of the test include:
- White blood cells: Part of the immune system that fights infections and other diseases
- Red blood cells (RBCs): Cell that carry oxygen throughout the body
- Hemoglobin (Hb): The iron-containing protein in RBCs that carries oxygen to tissues
- Hematocrit (Hct): The percentage of blood made up of red blood cells
- Platelets: Help form blood clots to slow or stop bleeding
This “alphabet soup” gives doctors important clues about your overall blood health. A CBC can detect signs of anemia, infection, inflammation, potential bleeding problems, or certain blood disorders, and it can help track the effectiveness of treatments.
If your CBC results are outside the normal range, it doesn’t automatically mean something serious. Sometimes the cause can be simple, but it may also point to certain health conditions.
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While a CBC is an important first step in detecting possible blood cancers, it is not enough by itself to confirm a diagnosis. Abnormal results typically prompt further tests—such as a peripheral blood smear, bone marrow biopsy, imaging, or genetic testing. These are necessary to confirm the presence, type and stage of cancer and guide steps for treatment. What are blood cancers?
Every three minutes, someone in the U.S. is diagnosed with blood cancer, which is an umbrella term that covers leukemia, lymphoma, and myeloma and other cancers that affect the blood and lymphatic system.
Although the specific causes remain largely unknown, scientists have learned that blood cancers develop when the DNA in immature blood cells becomes damaged or mutated. This triggers uncontrolled cell growth that crowds out healthy cells, leaving less room for normal blood production and weakening the immune system.
- Leukemia develops when the bone marrow makes large numbers of abnormal white blood cells that don’t work properly and crowd out healthy blood cells. Unlike most cancers, leukemia doesn’t form tumors.
- Lymphoma is a cancer of the lymphatic system, which helps remove excess fluid and produce immune cells. It begins when abnormal lymphocytes (a type of white blood cell) grow uncontrollably and build up in lymph nodes and other tissues.
- Myeloma affects plasma cells and disrupt normal antibody production, weakening the immune system and increasing infection risk.
Many blood cancers can start with vague or nonspecific symptoms such as fatigue, fever, night sweats, weight loss, or frequent infections. Because these symptoms are common to many less serious conditions, it can be difficult to recognize blood cancers early without blood tests or medical evaluation.
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