Blood Count (CBC) Test

What it is

Blood is mostly cells, and this test counts them. An analyzer reports how many red cells there are, how much hemoglobin they carry, what fraction of the blood volume they occupy and how large they average; how many white cells are present; and how many platelets. This code is the version that includes the differential, meaning the white cells are further sorted into their kinds. That extra step matters because the total white count only says there is a response going on, while the differential hints at what sort of response it is. If a result looks unusual, a technologist may put a smear under a microscope and look at the cells directly.

Why it is done

• To look for anemia, and to give a first hint at what is causing it from the size and hemoglobin content of the red cells
• To assess an infection or inflammation, where both the white count and the mix of white cell types carry information
• To check platelets when there is unusual bruising or bleeding, or before a procedure
• To monitor a known blood disorder or a treatment, such as chemotherapy, that suppresses the bone marrow

What to expect

A standard draw from a vein in the arm into a tube containing an anticoagulant so the sample does not clot. No fasting, no preparation. Most hospital labs return the numbers within an hour; outpatient labs typically within a day. Many values on the report sit slightly outside the printed reference range in perfectly healthy people, because those ranges are drawn to include most, not all, of the population.

Questions worth asking

• Was this ordered with the differential or without? They are separate codes, and the one with the differential costs more.
• If a manual smear review was added because the analyzer flagged something, is that a further charge on the bill?
• Is the lab running this in network? Blood drawn at an in-network clinic is sometimes processed by an out-of-network reference lab.
• During a hospital stay, how many CBCs have been drawn, and is each one itemized separately?