CBC with Differential

White blood cell count (WBC)

White blood cells are part of your immune system and help your body fight infection. This count shows how many are in a sample of your blood. It can rise with infection, inflammation, stress, or some medicines, and fall with some infections, medicines, or bone marrow conditions.

Why it’s measured: A general look at the immune cells that help your body fight infection.

Red blood cell count (RBC)

Red blood cells carry oxygen from your lungs to the rest of your body. This count shows how many are in a sample of your blood. It is read with hemoglobin and hematocrit, and it can be affected by iron, B12, and folate levels, blood loss, hydration, and where you live.

Why it’s measured: Counts the cells that carry oxygen, read together with hemoglobin and hematocrit.

Hemoglobin

Hemoglobin is the iron-containing protein inside red blood cells that carries oxygen. It is the main number used to check for anemia. Low iron, B12, or folate, blood loss, and some long-term conditions can lower it, while dehydration, smoking, and high altitude can raise it.

Why it’s measured: The main number used to check for anemia, read with the rest of the blood count.

Hematocrit

Hematocrit is the share of your blood volume made up of red blood cells. It usually moves in step with hemoglobin. Hydration affects it: being dehydrated can raise it, and extra fluid can lower it. It is read with hemoglobin and the red blood cell count.

Why it’s measured: Shows the share of your blood made up of red blood cells, read with hemoglobin.

Mean corpuscular volume (MCV)

MCV is the average size of your red blood cells. Smaller-than-usual cells are often seen with low iron, and larger-than-usual cells can relate to low B12 or folate, alcohol, thyroid or liver conditions, or some medicines. It helps a provider narrow down the type of anemia if one is present.

Why it’s measured: Average red cell size, which helps sort out types of anemia.

Mean corpuscular hemoglobin (MCH)

MCH is the average amount of hemoglobin inside each red blood cell. It is calculated from your hemoglobin and red blood cell count and tends to follow MCV: smaller cells usually carry less hemoglobin. It is one of the red cell indices a provider reads together.

Why it’s measured: Average hemoglobin per red cell, read with the other indices.

Mean corpuscular hemoglobin concentration (MCHC)

MCHC is the average concentration of hemoglobin inside your red blood cells, calculated from your hemoglobin and hematocrit. It shows how densely packed the cells are with hemoglobin. Like the other red cell indices, it adds detail when a provider reviews your blood count.

Why it’s measured: Shows how concentrated hemoglobin is inside your red cells, one of the red cell indices.

Red cell distribution width (RDW)

RDW shows how much your red blood cells vary in size. A higher value means a wider mix of small and large cells, which can happen when new cells are being made during a change in iron, B12, or folate levels. It is read with MCV and the rest of the blood count.

Why it’s measured: Shows how much your red cells vary in size, which can help sort out types of anemia.

Platelet count

Platelets are small cell fragments that help your blood clot and stop bleeding. This count shows how many are in your blood. It can rise with inflammation, low iron, or after an infection, and fall with some medicines, infections, or conditions that affect the bone marrow or spleen.

Why it’s measured: Counts the cell fragments that help your blood clot and stop bleeding.

Mean platelet volume (MPV)

MPV is the average size of your platelets. Newer platelets tend to be larger. On its own it says little, but a provider may read it alongside your platelet count to add context on how platelets are being made or used up.

Why it’s measured: Average platelet size, which a provider reads alongside your platelet count.

Neutrophils

Neutrophils are the most plentiful type of white blood cell and are often first to respond to bacterial infection and inflammation. The lab reports them as a percentage of your white cells and as an absolute count. Infection, stress, steroids, and exercise can raise them.

Why it’s measured: The white cells that often respond first to bacterial infection.

Lymphocytes

Lymphocytes are white blood cells that include B cells, which make antibodies, and T cells, which help direct the immune response. They often respond to viral infections. The lab reports them as a percentage and an absolute count, read with your other white cell results.

Why it’s measured: White cells that make antibodies and help direct the immune response.

Monocytes

Monocytes are white blood cells that move into tissues, where they help clear away germs and damaged cells. The lab reports them as a percentage and an absolute count. They can rise during recovery from infection and with some longer-term inflammatory conditions.

Why it’s measured: White cells that help clear germs and damaged cells from tissues.

Eosinophils

Eosinophils are white blood cells involved in allergic reactions and in fighting some parasites. The lab reports them as a percentage and an absolute count. They can rise with allergies, asthma, eczema, some medicines, and some infections, and a provider reads them in context.

Why it’s measured: White cells involved in allergic reactions and some infections.

Basophils

Basophils are the least common type of white blood cell. They release substances such as histamine during allergic and inflammatory reactions. The lab reports them as a percentage and an absolute count, and they are read as part of the full white cell differential.

Why it’s measured: The least common white cells, which take part in allergic and inflammatory reactions.

• Each marker next to the lab’s reference range
• Explained in plain language
• A licensed clinician reviews your order and, if appropriate, orders the test.
• A lab report you can download and share

An out-of-range count can need prompt follow-up with a healthcare provider, who reads the counts with your history and symptoms.