Complete Blood Count (CBC)

What happens if a change or abnormality is found

A complete blood count (CBC) is a blood test that measures the number and quality of red blood cells (RBCs or erythrocytes), white blood cells (WBCs or leukocytes) and platelets (thrombocytes).

A CBC includes the following information:

RBC count – the total number of RBCs
WBC count – the total number of WBCs
hemoglobin (Hb or Hgb) level – the total amount of hemoglobin in the blood
hematocrit (Hct) – the fraction of the blood made up of RBCs
mean corpuscular volume (MCV) – the average RBC size
mean corpuscular hemoglobin (MCH) – the average amount of hemoglobin per RBC
mean corpuscular hemoglobin concentration (MCHC) – the average concentration of hemoglobin per RBC
platelet count – the number of platelets
WBC differential count – the different types of WBCs expressed as a percentage

Why a CBC is done

A CBC may be done to:

provide information about a person’s general health
assess how well the blood-forming organs (for example, bone marrow and spleen) are functioning
check for anemia (a reduction in the number of healthy red blood cells)
check for infection
provide a baseline to compare with future CBCs during and after treatment
monitor the effects of therapy, especially therapies that can cause bone marrow suppression (a condition in which the bone marrow does not produce normal numbers of red blood cells, white blood cells and platelets)

How a CBC is done

A CBC test is usually done in a private laboratory or hospital laboratory. No special preparation is usually needed.

Blood is usually taken from a vein in the arm.
A tourniquet or elastic band is wrapped around the upper arm to apply pressure to the area and make the vein swell.
The person may be asked to open and close the fist to make the veins stand out more.
The skin is cleaned and disinfected.
A needle is inserted into the vein and a small amount of blood is removed.
- The person will feel a prick or stinging sensation.
The sample is collected in a tube and labelled with the person’s name and other identifying information.
The tourniquet is removed and the needle is withdrawn.
- Mild discomfort may be felt when the needle is withdrawn.
Pressure is applied to the area where the needle was inserted until bleeding stops.
A band aid may be applied.
The sample is sent to a laboratory to be analyzed by special machines, examined under a microscope or both.

Potential side effects

Potential side effects of having a CBC include:

bleeding
bruising
infection

What the results mean

Normal ranges may vary from person to person and laboratory to laboratory. Many factors can affect CBC results. An abnormal result will not necessarily identify the problem, so further investigation may be needed.

Common terminology to describe CBC results

Term	What it means
anemia	a reduction in the number of RBCs or hemoglobin content of RBCs
leukopenia	a reduction in the number of WBCs
leukocytosis	an increase in the number of WBCs
neutropenia	a decrease in the number of neutrophils
thrombocytopenia	a decrease in the number of platelets
thrombocytosis	an increase in the number of platelets

Abnormal CBC Values

Component	An increased value may be due to	A decreased value may be due to
WBC	infection leukemia some myeloproliferative disorders some types of cancer (for example, bronchogenic carcinoma) certain drugs, such as colony-stimulating factors stress, allergies, exercise or tissue injury can sometimes increase values	viral infections overwhelming bacterial infection bone marrow suppression caused by some drugs, chemotherapy or radiation therapy bone marrow disorders, such as leukemia or myelodysplastic syndrome (MDS) anemia immune system suppression
RBC	dehydration (such as from severe diarrhea) kidney disease some lung diseases polycythemia vera (a myeloproliferative disorder)	anemia due to: prolonged bleeding or blood loss (hemorrhage) insufficient dietary intake of iron or certain vitamins blood disorders chronic disease Hodgkin lymphoma and other lymphomas blood related cancers, such as: leukemia mulitple myeloma some myeloproliferative disorders
Platelets	prolonged bleeding or blood loss (hemorrhage) iron deficiency anemia infection (inflammation) surgical removal of the spleen (splenectomy) polycythemia vera (a myeloproliferative disorder) some types of leukemia	bone marrow disease diseases of the immune system bacterial infection viral infection chemotherapy radiation therapy multiple blood transfusions certain drugs, such as non-steroidal anti-inflammatory drugs (NSAIDs) including aspirin or ibuprofen

Note: Not all factors or conditions that can increase or decrease blood counts are listed above. Only the main cancer-related ones have been included.

What happens if a change or abnormality is found

The doctor will decide if more tests, procedures, follow-up care or treatment are needed. Sometimes therapies or doses may need to be adjusted to avoid complications if blood cell counts are low.

References

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