Complete blood count: what is included

In shortA complete blood count measures red blood cells, white blood cells, platelets, hemoglobin, hematocrit, and the average size of red blood cells (MCV). It is often part of a routine checkup and is used to monitor conditions and treatments that affect blood cell counts.

What this panel covers

A complete blood count is a group of measurements taken from one blood sample. It reports the red blood cells that carry oxygen from the lungs to the rest of the body; the white blood cells that fight infections and other diseases — a plain CBC gives the total white cell count, while a version called CBC with differential measures each of the five major white cell types separately; and the platelets that stop bleeding by helping the blood to clot.

Alongside the cell counts, the report includes hemoglobin — the iron-rich protein in red blood cells that carries oxygen — and hematocrit, the share of whole blood made up of red blood cells. It also gives the mean corpuscular volume (MCV), the average size of the red blood cells, which helps distinguish between different kinds of anemia.

The CBC is often part of a routine checkup, and it is used to monitor a condition or a treatment that may affect blood cell counts — infections, anemia, immune system disorders, and blood cancers among them. Because it looks at several cell lines at once, a single result is rarely read alone: the pattern across red cells, white cells, and platelets is what points in a direction.

Usually no special preparation is necessary. If the provider ordered other tests on the same blood sample, fasting for several hours may be needed — the provider says so. The sample is taken from a vein in the arm, and the draw itself takes only a few minutes.

Markers on the panel

Hemoglobin White blood cells (WBC)Red blood cells (RBC)Platelets (PLT)Hematocrit (Hct)

Why it is ordered

As part of a routine checkup, to monitor overall health, and to follow conditions or treatments that may affect blood cell counts — infections, anemia, immune system disorders, and blood cancers. It is one of the most frequently ordered laboratory tests.

How to prepare

Usually no special preparation is needed. If other tests are ordered on the same sample, fasting for several hours may be required — the provider's instructions take precedence.

How to read the report

A CBC report is a table of related numbers rather than one verdict. Each line is compared with the reference range printed by the laboratory, and the lines are read together: hemoglobin, hematocrit, and red cell indices describe the oxygen-carrying side; the white cell count (and the differential, when included) the immune side; platelets the clotting side. A value outside the range is a reason to look at the neighboring lines and the symptoms, not a diagnosis by itself.

Several markers on your report?

See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.

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Frequently asked questions

Does a CBC require fasting?

Usually not. Fasting for several hours may be needed only if other tests share the same blood sample — the provider will say so when ordering.

What does “CBC with differential” mean?

A plain CBC counts white blood cells in total. The differential version measures each of the five major white cell types separately, which gives more detail about infections and immune conditions.

What is MCV doing on the report?

MCV is the average size of the red blood cells. Together with hemoglobin it helps tell different kinds of anemia apart — small-cell and large-cell anemias have different causes.

Sources

Complete Blood Count (CBC): MedlinePlus Medical Test — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.