Complete Blood Count

A complete blood count (CBC) is a common blood test used by doctors to screen for a variety of conditions including:

  • Anemia
  • Bone disorders
  • Malnutrition (such as vitamin or mineral deficiencies)
  • Infections
  • Inflammation
  • Autoimmune disorders
  • Leukemia and lymphoma
  • Sickle cell anemia

A CBC evaluates your overall health by measuring several components of your blood, including:

  • Red blood cells
  • White blood cells
  • Hemoglobin
  • Platelets

Abnormalities in these blood levels may indicate the presence of an underlying health condition. In some cases, your provider may adjust any medication you may be taking in light of the results of your CBC.

Unlike other labs and blood tests, CBCs do not require fasting before your appointment.

Complete blood counts are commonly performed by your primary care provider as a part of your routine yearly check-up. A complete blood count can help doctors to:

  • Detect underlying health conditions
  • Monitor pre-existing health conditions
  • Monitor the effects of medication usage that affects blood count

If you are managing a pre-existing condition - such as a blood disorder - your doctor may order more frequent CBCs to help track and treat the condition. Additionally, you may want to ask about a complete blood count if you are experiencing persistent symptoms such as:

  • Fatigue
  • Dizziness
  • Weakness
  • Joint pain
  • Unexplained bruising or bleeding
  • Unexplained swelling anywhere on the body
  • Irregular heart rhythms
  • Fever
  • Nausea & vomiting

Complete blood counts do not require you to fast before your appointment. If your doctor has ordered additional testing, you may be asked to fast. However, if you are just undergoing a CBC, no preparation is needed. You can eat or drink as normal.

During the appointment, your health care provider will swab your arm clean with alcohol and insert a needle into the forearm to draw blood. As the needle is inserted, you may feel a slight pinch, but this should be all the discomfort you experience during the procedure. The drawn blood will be deposited into a vial or test tube, which is then sent to the lab for testing. After the desired amount of blood has been drawn, the needle will be taken out of your arm, and the puncture site will be cleaned and bandaged.

Because no anesthesia is used during a complete blood count, you can resume everyday activities right after your blood is drawn. You may experience some soreness in your arm where the needle was inserted, but this usually goes away within a few hours.

You will usually get the results of your complete blood count within a business day or two of your appointment. If needed, your provider may ask for follow-up testing.

Normal, healthy ranges of a blood cell count for adults over the age of 15 are:

Red blood cell count

Men: 4.7 to 6.1 million cells per microliter (mcL)
Women who aren’t pregnant: 4.2 to 5.4 million mcL

Hemoglobin (The protein in red blood cells that carries oxygen)

Men: 13.0 - 17.0 g/dL (grams per deciliter)
Women: 11.5 - 15.5 g/dL (grams per deciliter)

Hematocrit (Concentration of red blood cells)

Men: 40 - 55%
Women: 36 - 48%

White blood cell count

3,400 to 9,600 cells/mcL

Platelet count

Men: 135,000 to 317,000/mcL
Women: 157,000 to 371,000/mcL

If your results show numbers outside this range, you may be asked to come back to your health care provider’s office for follow-up testing. A CBC is not a definitive test, meaning it is not the sole method doctors use in diagnosing medical conditions. In some cases, numbers just outside the “normal” range of healthy blood counts in otherwise healthy individuals may not be a cause for concern. Similarly, individuals undergoing cancer treatment or pregnant women may produce blood count numbers outside these ranges. In these cases, a doctor may adjust treatment or medication to balance blood levels.

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