Blood Test (CBC)

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 A small quantity of blood is withdrawn into a sterile vial or a test tube.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.