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Complete blood count (CBC)

What is a complete blood count (CBC)?

A CBC test quantifies red as well as white blood cells along with platelets in the blood, which can aid diagnose medical conditions or diseases such as leukaemia, thalassemia, and anaemia. It is also useful for tracking progress or helping manage already existing conditions such as infection, or blood disorders. 

A CBC estimates several components of blood, comprising:

  • Red blood cells (or Erythrocytes), which carries oxygen from lungs to the remaining body.
  • White blood cells (or Leucocytes), which combat infections as well as other diseases. There are five predominant types of white blood cells. A CBC test estimates the total number of white cells in blood. A different test known as CBC with differential estimates the number of each type of these white blood cells.
  • Platelets (or Thrombocytes), which impede bleeding by aiding blood to clot.
  • Hemoglobin, (a protein/pigment) transports oxygen from lungs to the rest of the body.
  • Hematocrit, an estimation of how much blood is made up of red blood cells.
  • Mean corpuscular volume (MCV), an estimate of the average size of red blood cells.

A healthcare professional may advise a CBC for routine health checkups or investigation of manifestations like bruising, swelling, irritation, blood pressure issues, fever (pyrexia), dizziness, and tiredness.

What happens during the procedure of a complete blood count (CBC)?

A health care professional will withdraw a blood sample from a vein in an individual's arm, utilizing a tiny needle. Post the needle is inserted, a minute quantity of blood will be collected into a vial. Individuals may feel a little sting when the needle goes in or out. This usually takes less than four to five minutes.

Will an individual be required to do anything to prepare for the test?

Generally, there is no special preparation required for a complete blood count. But if healthcare provider ordered other tests on blood sample, you may need to fast (not consume food or liquid) for several hours prior to the test. The healthcare provider will inform the individual if there are any special instructions to follow.

Normal Results

Blood counts may vary with altitude. In general, normal results are:

Blood component


Standard range

RBC count


4.7 to 6.1 million cells/mcL

RBC count


4.2 to 5.4 million cells/mcL

WBC count

Irrespective of Gender

4,500 to 10,000 cells/mcL



40.7% to 50.3%



36.1% to 44.3%



13.8 to 17.2 gm/dL



12.1 to 15.1 gm/dL

Platelet count

Irrespective of gender

150,000 to 450,000/dL


The examples above are predominant measurements for results of these tests. Normal value ranges may differ slightly among distinct laboratories. 

What Do Abnormal Results Mean?

Elevated RBC, hemoglobin, or hematocrit maybe because of:

  • A dearth of plenty of water and fluids, such as from severe diarrhea, excessive perspiration, or water pills utilised to treat high blood pressure.
  • Renal disease with high erythropoietin production.
  • Low level of oxygen in the blood for a long time, most often due to heart or lung ailment, long term exposure to carbon monoxide, or residing at a high altitude.
  • Polycythaemia vera
  • Smoking
  • Testosterone use/Androgen use

Low RBC, haemoglobin, or haematocrit is an indication of anaemia, which can result from:

  • Loss of blood (either sudden, or from problems like heavy menstrual periods over a long duration)
  • Bone marrow failure (for instance, from infection, or tumor)
  • Breakdown of red blood cells
  • Cancer as well as its treatment
  • Certain long-term (chronic) medical conditions, like chronic renal ailment, ulcerative colitis, or rheumatoid arthritis.
  • Leukemia
  • Chronic infections like hepatitis
  • Poor diet as well as nutrition, causing too little iron, folate, or vitamin B12.
  • Multiple myeloma

A lower than usual white blood cell count is known as leukopenia. A reduced WBC count may be due to:

  • Abuse of alcohol
  • Autoimmune diseases 
  • Bone marrow failure 
  • Chemotherapy medicines 
  • Liver diseases
  • Enlarged spleen
  • Infections caused by viruses, like mono or AIDS.

An elevated WBC count is known as leukocytosis. It can result from:

  • Corticosteroids
  • Infections
  • Diseases like lupus, rheumatoid arthritis, or allergy
  • Leukemia
  • Severe emotional or physical stress
  • Tissue damage (for instances from burns)

An elevated platelet count maybe because of:

  • Bleeding
  • Diseases like cancer or blood disease
  • Deficiency of Iron
  • Issues with the bone marrow

A decreased platelet (thrombocyte) count may be due to:

  • In case of Disorders where platelets are destroyed
  • Enlarged spleen.
  • Failure of bone marrow
  • Pregnancy
  • Chemotherapy medicines 

CBC Test: Risks Involved

There is very little risk involved with having blood withdrawn. Veins and arteries differ in size from one individual to another, and from one side of the body to the other. Withdrawing blood from some individuals may be tougher than from others.

Other risks involved with having blood drawn are slight, but may comprise:

  • Too much bleeding
  • Feeling lightheaded
  • Hematoma (blood collecting below the skin)
  • Infection 


RBCs transport hemoglobin which, in turn, transports oxygen. The quantity of rely received by tissues of body relies on the amount as well as the function of RBCs as well as haemoglobin.

WBCs are mediators of inflammation as well as the immune response. There are several types of WBCs that are generally observed in the blood:

  • Neutrophils 
  • Band cells 
  • T-type lymphocytes (T cells)
  • B-type lymphocytes (B cells)
  • Monocytes
  • Eosinophils
  • Basophils

In a nutshell, a complete blood count is a common blood test that is generally part of a regular health checkup. Complete blood counts can aid detect various disorders comprising infections, anaemia, diseases of the immune system, and blood cancers. The CBC test isolates as well as counts the 7 different cell types present in the blood: red blood cell, neutrophil, eosinophil, basophil, lymphocyte, monocyte, and platelet.


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