Health information to help you understand symptoms. It isn't a diagnosis.
Check symptoms

Complete blood count (CBC)

Also called: CBC, Full blood count, Hemogram

A complete blood count (CBC) measures your red blood cells, white blood cells, and platelets. It's one of the most common blood tests.

SampleA small tube of blood from a vein in your arm
Fasting?Usually not needed
ResultsOften the same day
Good to knowOne result rarely tells the whole story. Your provider looks at your results together with your symptoms, exam, and other tests.

What the test is

A CBC gives a broad picture of your health. It can show anemia, infection, inflammation, bleeding problems, and some blood cancers.

A 'CBC with differential' also counts each type of white blood cell.

What it measures

  • Red blood cells, hemoglobin, and hematocrit, which carry oxygen
  • Red cell size (MCV) and other red cell measures
  • White blood cells, which fight infection
  • Platelets, which help blood clot

Why it's done

  • As part of a routine checkup
  • To look for anemia when you feel tired or weak
  • To look for infection or inflammation
  • To check for bleeding or bruising problems
  • To monitor treatments that can affect blood counts, like chemotherapy

Getting ready and what happens

  • No special preparation is usually needed.
  • Tell your provider about medicines and supplements you take.

How the test is done

  • A health worker cleans the skin, puts a band around your arm, and draws blood from a vein with a small needle. It takes a few minutes.

What the results mean

ResultTypical range for adults
HemoglobinMen about 13.5 to 17.5 g/dL; women about 12.0 to 15.5 g/dL
HematocritMen about 41% to 50%; women about 36% to 44%
White blood cellsAbout 4,500 to 11,000 per microliter (4.5 to 11.0)
PlateletsAbout 150,000 to 450,000 per microliter (150 to 450)
MCV (red cell size)About 80 to 100 fL

Normal ranges vary from lab to lab and can differ by age, sex, and pregnancy. Your report lists your lab's own range next to each result. A result a little outside the range is often not a problem.

Low red blood cells or hemoglobin

This is anemia. Causes include low iron, low B12 or folate, blood loss, kidney disease, and long-term illness. Red cell size (MCV) helps narrow the cause.

High white blood cells

Often from infection, inflammation, stress, smoking, or steroid medicines. Rarely, very high counts can point to a blood cancer.

Low white blood cells

Can come from viral infections, some medicines, autoimmune disease, or bone marrow problems. Very low counts raise infection risk.

Low or high platelets

Low platelets can cause easy bruising and bleeding. High platelets can follow infection, inflammation, or iron deficiency.

When a result needs quick action

Call 911Fever with a very low white count during chemotherapy, or heavy bleeding with very low platelets
Call your provider todayA result your provider calls critical, or new shortness of breath, dizziness, or chest pain with low hemoglobin

Questions to ask your provider

  • What do my results mean for me?
  • Do I need to repeat this test or have other tests?
  • Is my result high or low enough to need more tests?
  • Could my medicines affect my counts?
  • Do I need iron, B12, or other tests?

Risks

A blood draw is very safe. You may have slight pain or a small bruise where the needle went in.

Related conditions

Related medicines

Related tests

Sources

Last updated 2026-11-13.