Is a CBC the same as a full blood count?

Yes. Complete blood count (CBC) is the usual US name and full blood count (FBC) the usual UK name for the same group of tests.

Do I need to fast for a CBC?

Usually not, MedlinePlus says — unless other tests are being done on the same sample. Follow the instructions you were given.

What is a CBC with differential?

A CBC that also counts each of the five main types of white blood cell, rather than just the total.

CBC / FULL BLOOD COUNT

CBC blood test results explained

A complete blood count (CBC) — called a full blood count (FBC) in the UK — measures your red blood cells, white blood cells and platelets, plus hemoglobin, hematocrit and the average size of your red cells (MCV). It is one of the most common blood tests and is often part of a routine check-up.

Why it’s confusing

A CBC report can run to 20 lines of abbreviations — RBC, Hgb, Hct, MCV, MCH, MCHC, RDW, PLT, WBC and a differential — with flags scattered through it.

Many of these lines are related. Several describe red cells in different ways, so one underlying change can flag several lines at once.

How to read it

Red cells: RBC is the number of red blood cells, which carry oxygen. Hemoglobin (Hb or Hgb) is the iron-rich protein inside them that carries the oxygen. Hematocrit (Hct) is the proportion of your blood made up of red cells.

Red cell indices: MCV is the average size of red cells; MCH and MCHC describe how much hemoglobin they hold. RDW, where reported, describes how much red cell size varies.

White cells: WBC is the total number of white blood cells, which fight infection. A “CBC with differential” also counts each of the five main types.

Platelets (PLT): cells that help blood clot.

MedlinePlus notes that results outside the range don’t always mean a condition that needs treatment — diet, activity, medicines, menstrual periods and not drinking enough water can all affect them.

What it does not mean

That a flag on one line is a diagnosis. Your doctor looks at the lines together and with your history.
That a normal CBC rules everything out. It is one tool among many.
That UK and US reports are directly comparable. Units can differ (g/L versus g/dL for hemoglobin, for example).

Where you’ll see it

Routine blood test reports, often at the top of the results.
Hospital and GP results in a patient portal or the NHS App.

Questions worth asking

Ask your doctor

Which of these results matter for me?
Are any flagged results related to each other?
Do I need a repeat test?

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Common questions

Is a CBC the same as a full blood count?: Yes. Complete blood count (CBC) is the usual US name and full blood count (FBC) the usual UK name for the same group of tests.
Do I need to fast for a CBC?: Usually not, MedlinePlus says — unless other tests are being done on the same sample. Follow the instructions you were given.
What is a CBC with differential?: A CBC that also counts each of the five main types of white blood cell, rather than just the total.

Sources

Reading a scan report rather than a blood test or letter? Radily’s radiology report phrase guides explain the wording radiologists use.