Complete Blood Count (CBC)
One of the most commonly ordered blood tests, the CBC measures several components of the blood to give a broad overview of overall health.
Last medically reviewed: April 10, 2026 | Reviewed by LabResult.MD Editorial Team
What is a CBC?
A Complete Blood Count (CBC) is a blood test that measures the number and types of cells in the blood. It is one of the most frequently ordered lab tests and provides important information about overall health.
A CBC can help detect a wide range of conditions, from infections and anemia to blood cancers. It is often part of a routine health checkup, but a healthcare provider may also order it to investigate specific symptoms like fatigue, weakness, bruising, or fever.
What Does a CBC Measure?
A CBC typically includes the following components:
Red Blood Cells (RBC)
Red blood cells carry oxygen from the lungs to the rest of the body and bring carbon dioxide back to the lungs to be exhaled.
Typical range: Men: 4.7 – 6.1 million cells/mcL • Women: 4.2 – 5.4 million cells/mcL
Hemoglobin (Hgb)
The protein in red blood cells that carries oxygen. Hemoglobin levels are a key indicator for anemia.
Typical range: Men: 13.5 – 17.5 g/dL • Women: 12.0 – 16.0 g/dL
Hematocrit (Hct)
The percentage of blood volume that is made up of red blood cells. Like hemoglobin, this helps evaluate anemia and hydration status.
Typical range: Men: 38.3% – 48.6% • Women: 35.5% – 44.9%
White Blood Cells (WBC)
White blood cells are part of the immune system and help the body fight infections. The CBC measures the total WBC count and may also include a differential that breaks down the five types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
Typical range: 4,500 – 11,000 cells/mcL
Platelets
Platelets are cell fragments that help blood clot. Abnormal platelet counts can indicate bleeding disorders, bone marrow problems, or other conditions.
Typical range: 150,000 – 400,000 cells/mcL
Mean Corpuscular Volume (MCV)
The average size of red blood cells. MCV helps classify the type of anemia: small red blood cells (microcytic) may suggest iron deficiency, while large red blood cells (macrocytic) may suggest vitamin B12 or folate deficiency.
Typical range: 80 – 100 fL
CBC Reference Ranges at a Glance
Reference ranges may vary by laboratory, testing method, age, sex, and other factors. Always use the ranges provided on your lab report.
| Component | Men | Women | Units |
|---|---|---|---|
| RBC | 4.7 – 6.1 | 4.2 – 5.4 | million cells/mcL |
| Hemoglobin | 13.5 – 17.5 | 12.0 – 16.0 | g/dL |
| Hematocrit | 38.3% – 48.6% | 35.5% – 44.9% | % |
| WBC | 4,500 – 11,000 | cells/mcL | |
| Platelets | 150,000 – 400,000 | cells/mcL | |
| MCV | 80 – 100 | fL | |
When is a CBC Ordered?
A healthcare provider may order a CBC as part of:
- Routine annual health checkups
- Evaluation of symptoms like fatigue, weakness, fever, bruising, or bleeding
- Monitoring chronic conditions such as kidney disease or cancer
- Checking blood counts before or after surgery
- Monitoring the effects of medications that may affect blood cells (such as chemotherapy)
- Investigating suspected infections or immune system problems
What Abnormal Results May Mean
Abnormal CBC values can point to many different conditions. A single abnormal value does not necessarily mean there is a problem — results are usually interpreted together and in the context of symptoms and medical history.
High values could indicate
- Dehydration (high RBC/Hct)
- Bone marrow disorders (polycythemia)
- Infection or inflammation (high WBC)
- Bone marrow disorders (high platelets)
Low values could indicate
- Anemia (low RBC/Hgb/Hct)
- Iron, B12, or folate deficiency
- Immune deficiency or bone marrow problems (low WBC)
- Bleeding disorders or autoimmune conditions (low platelets)
Frequently Asked Questions
What does a CBC blood test measure?
A Complete Blood Count measures red blood cells (RBC), hemoglobin, hematocrit, white blood cells (WBC), platelets, and mean corpuscular volume (MCV). It provides a broad overview of blood health and can help detect anemia, infection, clotting disorders, and blood cancers.
How often should you get a CBC?
For healthy adults, a CBC is typically included as part of an annual physical exam. People with chronic conditions, those taking medications that affect blood cells, or those with symptoms like unexplained fatigue or bruising may need more frequent testing.
Do you need to fast before a CBC?
No, fasting is generally not required for a CBC. However, if a CBC is ordered alongside other tests that do require fasting (like a metabolic panel or lipid panel), your healthcare provider may ask you to fast.
Related Biomarkers and Panels
Sources
- MedlinePlus. Complete Blood Count (CBC). U.S. National Library of Medicine
- American Society of Hematology. Blood Basics
- Mayo Clinic. Complete blood count (CBC)
Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice. Reference ranges vary by laboratory. Always discuss your results with a qualified healthcare provider.