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Complete Blood Count (CBC) Test

Last updated April 8, 2018

Approved by: Krish Tangella MD, MBA, FCAP

A Complete Blood Count (CBC) Test gives vital information through numerical values of the key blood components.


What are the other Names for this Test? (Equivalent Terms)

  • CBC (Complete Blood Count) Test
  • FBC (Full Blood Count) Test
  • Full Blood Picture (FBP) Test

What is Complete Blood Count (CBC) Test? (Background Information)

  • Blood is the most important human body fluid because it transports oxygen and nutrients to all parts of the body. It also helps in the immunity process and cleans the body of waste products, like ammonia, carbon dioxide, etc.
  • Blood is a complex tissue that is composed of over 4000 components - the significant ones being:
    • Red blood cells (RBC)
    • White blood cells (WBC)
    • Platelets
    • Blood plasma
  • Geographic or regional distribution does not affect the universality of blood
  • A Complete Blood Count (CBC) Test gives vital information through numerical values of the key blood components
  • It is one of the most commonly ordered blood test, to understand an individual’s general health status; but, holds importance for revealing disorders, like anemia, infection, and conditions, such as fatigue, drowsiness, general malaise, etc.
  • Special automatic machines rapidly analyze the blood sample and list a count of these main constituents: RBC (including hemoglobin), WBC (differential and leukocyte), and platelets
  • These are then checked against baseline/normal value ranges to determine the individual’s blood health status, abnormal cell counts, etc. Very high or very low values may be pointers to specific medical issues

What are the Clinical Indications for performing the Complete Blood Count (CBC) Test?

A Complete Blood Count Test normally forms part of a routine health check-up process. Additionally, the following specific situations may warrant a CBC Test:

  • To help diagnose blood-related illnesses, like anemia, leukemia, etc. Alternatively, if the patient has symptoms of fatigue, exhaustion, and other such symptoms, the test may be ordered
  • To understand and monitor the effect of medication, chemotherapy, and radiotherapy on blood
  • To help diagnose infections
  • To investigate the severity of a blood loss, internal bleeding, hemorrhage, or blood-clotting

How is the Specimen Collected for Complete Blood Count (CBC) Test?

Sample required: Blood

Process: Insertion of needle into a vein (arm) or, by pricking an infant’s heel, or by using the finger stick (finger prick) method for adults and children.

Preparation required: None

What is the Significance of the Complete Blood Count (CBC) Test Result?

The Complete Blood Count Test provides a 'full blood picture' and a general understanding of an individual’s health. The normal range varies between the sexes (men and non-pregnant women), and is different for young children and neonates (newborns). Any high or low blood count values may be probed further, or corroborated by additional investigations.

Following are interpretations of the result:

  • High RBC count means that there is an excess RBC production, or it may be due to loss of other body fluids caused by diarrhea, dehydration, etc.
  • Low RBC count is a strong indication of anemia; however, further investigations are required to confirm the same
  • High WBC count could be due to infections, blood cancer, etc.
  • Below average levels of WBC, are due to bone marrow issues, effect of medications, liver/spleen diseases, excess alcohol intake, severe viral or other infections, autoimmune disorders, etc.
  • Platelet production may be affected, if there is an increase or decrease due to chemotherapy, bleeding, leukemia, genetic disorders (like Wiskott-Aldrich or Bernard-Soulier Syndromes), hyperspleenism, and pernicious anemia

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • It should be understood that human blood cell count populations are generally not affected by lifestyle modifications
  • They remain the same, unless there is a health issue, or a deficiency in important vitamins and minerals in the body
  • A healthy life, in most cases, ensures that the blood components are within their normal ranges

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Feb. 3, 2014
Last updated: April 8, 2018