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What is a Complete Blood Count test?

Complete blood count (CBC) is a blood test that helps evaluate the number of circulating blood cells and the amount of haemoglobin present in red blood cells (RBCs). 

Multiple conditions, such as anaemia, leukaemia, platelet deficiency, bacterial infections can be diagnosed using a CBC test by assessing abnormalities in blood cell counts. Infections and allergies can also be distinguished when a differential WBC count is performed.

  1. Why is a CBC test performed?
  2. How do you prepare for a CBC test?
  3. How is CBC performed?
  4. What do CBC test results indicate?

CBC is performed for several reasons, as it evaluates multiple components of blood. It helps in: 

  • Diagnosing medical conditions: CBC helps diagnose the underlying conditions responsible for various symptoms, especially those associated with fever, inflammation, fatigue, weakness, bruising or bleeding.
    • An RBC count along with haemoglobin helps in diagnosing anaemia and distinguishing its types.
    • A WBC count helps in diagnosing infections, whereas a differential WBC count helps in distinguishing bacterial, viral and parasitic infections.
    • Platelet levels help in assessing bleeding and clotting disorders.
  • Monitoring medical conditions: CBC helps in close monitoring of blood count in case of blood disorders such as leukaemia. It is usually recommended, to keep tabs on the severity of the condition.
  • Monitoring medical treatment: Blood count, when performed sequentially or at regular intervals, can help in evaluating response to a treatment, particularly for bacterial infections and blood disorders.

No special preparations are needed for this test.

It is a simple test that takes less than five minutes. An experienced laboratory specialist collects a blood sample from a vein in your arm by inserting a small needle. A small quantity of blood is withdrawn into a sterile vial or a test tube. A momentary pricking pain is experienced when the needle goes into the vein.

There is a minimal risk of pain, light-headedness or bruising at the site of injection. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of blood withdrawal.[1]In latter cases, it is important to check in with a doctor at the earliest to prevent further spread of infection.

CBC test results vary between various age groups and there are minor differences in blood counts for men and women. 

Normal levels:

  • Haemoglobin
    • Men: 13-16 g/dL
    • Women: 11.5-14.5 g/dL
  • RBC
    • Men: 4.32 to 5.72 million/mL
    • Women: 3.92 to 5.13 million/mL
  • WBC
    • 4,000-11,000 cells/mL
  • Platelet
    • 1.5-4.5 lakhs/mL

Abnormal results:

Few conditions leading to higher values in various components of a CBC test are mentioned below:

  • Haemoglobin: People residing at higher altitudes or in chronic smokers
  • RBC count: Polycythemia vera, heart disease or recent blood loss events
  • WBC count: Infections (usually bacterial), inflammation, bone marrow disorder, immune system disorder or leukaemia
  • Platelet count: Rare but usually indicates side effects of medications

Few conditions leading to lower values in various components of a CBC test are mentioned below:

  • Haemoglobin: Anaemia; a combination of haemoglobin, haematocrit and RBC count for distinguishing the type of anaemia
  • RBC count: Haemolytic anaemia and acute blood loss
  • WBC count (leukopenia): Bone marrow diseases, autoimmune diseases as well as cancers
  • Platelet count (thrombocytopenia): Haemophilia, infections (dengue or malaria) or thrombocytopenia purpura

CBC is not a definitive diagnostic test. It is usually recommended along with other tests. Several conditions alter cell counts, which may or may not require treatment. Normal values of cell counts vary according to age as well as the device used for evaluating blood count, it is important to consider the reference range for better data interpretation.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from the educational perspective and is in no way a substitute for medical advice from a qualified doctor.

Blood Test (CBC) की जांच का लैब टेस्ट करवाएं

CBC (Complete Blood Count)

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References

  1. Yuko, S. et. al. (2013 October). Examination of the Percentage of Immature Platelet Fraction in Term and Preterm Infants at Birth J Clin Neonatol. 2013 Oct-Dec; 2(4): 173–178.
  2. Adeli K, Raizman JE, Chen Y, Higgins V, Nieuwesteeg M, Abdelhaleem M, Wong SL, Blais D. Clin Chem. 2015 Aug;61(8):1075-86. PMID: 26044509
  3. CLSI. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline, Third Edition. CLSI document EP28-A3c. Wayne, PA, Clinical and Laboratory Standards Institute, 2008
  4. Soldin J, Brugnara C, Wong EC: Pediatric Reference Intervals. Fifth Edition. AACC Press. Washington, DC, 2005. ISBN 1-594250-32-4
  5. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Complete Blood Count (CBC)
  6. Bain B J. The peripheral blood smear. In Goldman L, Schafer AI. (© 2012). Goldman's Cecil Medicine 24th Edition: Elsevir Saunders, Philadelphia, PA. Pp 1024-1031.7
  7. Pagana, Kathleen D., Pagana, Timothy J., and Pagana, Theresa N. (© 2015). Mosby's Diagnostic and Laboratory Test Reference 12th Edition: Mosby, Inc., Saint Louis, MO. Pp 497-501, 786-789, 991-995.
  8. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Anemia
  9. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Lymphocytopenia
  10. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Thrombocytopenia
  11. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Thrombocythemia and Thrombocytosis
  12. Sakurai Yuko, Tomohiro Takeda et al. Examination of the Percentage of Immature Platelet Fraction in Term and Preterm Infants at Birth. J Clin Neonatol. 2013 Oct-Dec; 2(4): 173–178. PMID: 24404529
  13. Hoffman, J.J. (2014).Reticulated platelets: analytical aspects and clinical utility. Clin Chem Lab Med. 2014; 52(8):1107-17.
  14. Keohane, E, Smith, L. and Walenga, J. (© 2016). Rodak's Hematology Clinical Principles and Applications 5th Edition: Elsevier Saunders, Saint Louis, MO. Pp 145, 173.