Complete Blood Count (CBC) Test

A complete blood count (CBC) measures the number and size of different cells in your blood, including red blood cells, white blood cells, and platelets. It helps check your overall health and detect conditions like anemia, infection, or blood disorders.

What this test measures

A CBC measures red blood cells (which carry oxygen), white blood cells (which fight infections), platelets (which help blood clot), hemoglobin (an iron-rich protein that carries oxygen), hematocrit (the amount of whole blood made of red blood cells), and mean corpuscular volume (MCV, the average size of red blood cells).

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

A high white cell count may be a sign of an infection or a reaction to a medicine.

Lower-than-normal results

A low white cell count may be a sign of an autoimmune disorder, bone marrow disorder, or cancer.

Frequently asked questions

What is a complete blood count (CBC)?

A CBC is a group of blood tests that measure the number and size of different cells in your blood.

What does a CBC measure?

It measures red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and mean corpuscular volume (MCV).

Why is a CBC done?

It is often part of a routine checkup and is used to monitor conditions like infections, anemia, immune system disorders, and blood cancers.

What can cause abnormal CBC levels?

Abnormal levels may be due to dehydration, anemia, heart disease, infection, medicines, or other factors. They don't always mean a medical condition needs treatment.

What does a high white blood cell count mean?