Complete Blood Count (CBC)
Reviewed
Also called: CBC, Full blood count, FBC, Blood cell count
A complete blood count measures red cells, white cells, platelets, haemoglobin, haematocrit, and selected cell indices.
Specimen: Blood
Why this test may be ordered
- Routine health assessment
- Investigation of infection, anaemia, bleeding, or fatigue
- Monitoring an illness or treatment that may affect blood cells
Preparation and collection
A CBC alone usually needs no special preparation. Follow instructions if other tests are being collected at the same time.
A health professional usually takes a small blood sample from a vein. Collection normally takes only a few minutes.
Blood collection has a small risk of brief discomfort, bruising, light-headedness, or rarely infection at the needle site.
Understanding results
A CBC contains several related measurements. Results should be interpreted together using the performing laboratory's intervals and the person's symptoms, history, age, medicines, and previous results.
- One or more values outside range: May reflect many causes including infection, anaemia, inflammation, bleeding, hydration changes, medicine effects, or bone-marrow disorders. Limitation: A CBC pattern is not a diagnosis and a single abnormality may be temporary. Next step: Clinical review, comparison with prior results, and targeted follow-up tests when appropriate.
- Values within the printed range: Measured components fall within that laboratory's stated interval. Limitation: A result within range does not exclude every illness and may not represent the person's usual baseline. Next step: Interpret with the reason for testing and symptoms.
- 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.
- Which reference interval and units apply to my result?
- Could medicines, supplements, illness, or sample timing affect this result?
- Do I need a repeat test or another test before any conclusion is made?
Evidence source
U.S. National Library of Medicine: Complete Blood Count (CBC)