Complete Blood Count (CBC) Test

About this test

A CBC is one of the most commonly ordered blood tests. It counts and evaluates all three major cell types in your blood — red cells, white cells, and platelets — and provides key measurements about their size and health. It's often part of a routine annual check-up and is also ordered when investigating fatigue, infection, bruising, or unexplained symptoms.

The CBC doesn't diagnose a specific condition on its own, but abnormal patterns — such as low hemoglobin, high white blood cell count, or low platelets — guide your clinician toward a diagnosis and the right next steps.

Components

• Red Blood Cell (RBC) Count, Hemoglobin, and Hematocrit: These three markers reflect your blood's oxygen-carrying capacity. Low values indicate anemia; high values can suggest dehydration or a bone marrow condition.
• RBC Indices (MCV, MCH, MCHC, RDW): Describe the size and hemoglobin content of red blood cells. These help identify the type of anemia — for example, small pale cells (low MCV) suggest iron deficiency, while large cells (high MCV) suggest B12 or folate deficiency.
• White Blood Cell (WBC) Count and Differential: Counts the five types of white blood cells (neutrophils, lymphocytes, monocytes, eosinophils, basophils). Elevated or reduced counts, or an abnormal mix of cell types, can indicate infection, inflammation, immune disorders, or blood cancers.
• Platelet Count and Mean Platelet Volume (MPV): Platelets help your blood clot. Low counts increase bleeding risk; high counts can increase clotting risk. MPV reflects platelet size, which can add diagnostic detail.

Who is this test for?

The CBC is one of the most commonly ordered blood tests and is a standard part of routine annual care. It is appropriate for adults of any age who want to check their red blood cells, white blood cells, and platelets. It is also commonly ordered when someone is experiencing fatigue, recurring infections, unexplained bruising, or unusual bleeding.