Complete Blood Count (CBC)
Reviewed
A complete blood count measures red cells, white cells, platelets, haemoglobin, haematocrit, and selected cell indices.
Preparation and collection
A CBC alone usually needs no special preparation. Follow instructions if other tests are being collected at the same time.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- Reference intervals vary by laboratory, age, pregnancy status, altitude, and other factors.
- Recent illness, exercise, hydration, menstruation, medicines, and sample quality can affect results.
What to do next
A clinician may request a differential count, blood film, iron studies, reticulocytes, or other targeted tests based on the pattern.
Evidence source
U.S. National Library of Medicine: Complete Blood Count (CBC)