Home Health A-Z What is the Significance and Importance of Performing a Complete Blood Count Test?

What is the Significance and Importance of Performing a Complete Blood Count Test?

Verified By Apollo Doctors July 7, 2021 16321 0
Complete Blood Count
Complete Blood Count

The CBC or Complete Blood Count is a blood test that helps doctors evaluate the overall health of a patient. It is also used to detect any sort of disorder in the patient, such as leukemia or anemia, which is often caused due to lower red blood cells count. 

A CBC is usually done as a routine checkup under annual health maintenance of the patient. Patients who experience symptoms like fever, weakness, or fatigue are often asked to get a CBC done. This test helps the doctors detect if there is any infection in your bloodstream. CBC is also done to assess the progress of on-going medical treatment. Treatments like chemotherapy that affect your blood levels need to be monitored to see if they are helping you or not.

What happens during a Complete Blood Count test? 

The CBC test is just like any other blood test. A nurse will take a sample of your blood from a vein of your arm. This sample will be processed at a lab for review. There is no special diet that needs to be followed prior to this CBC  test. You are encouraged to eat and drink as you normally would to see how your routine diet affects your blood. The test will take only a few minutes, after which you can get back to your daily work. The amount of blood taken is not enough to make you dizzy. If the provider has ordered other blood work along with CBC then you may need to fast.  

What is the Purpose of a Complete Blood Count?

There are multiple reasons why the CBC test is done. Some of them are as follows:

  • To give an overall report of the patient’s health: CBC is often recommended as a part of a complete medical examination. This will help your doctor to analyze  your overall health.
  • To help diagnose medical conditions: If you are sick, your doctor will recommend performing a CBC to help diagnose the problem or underlying medical condition or possible etiology of falling sick and help to determine the WBCs count in the blood. . This is done when the patient is experiencing symptoms of fatigue, fever, weakness, or even internal bleeding. 
  • To monitor how medical treatment is working: A CBC can only monitor certain medical treatments. This allows the doctors to monitor how well the treatment is working based on how your blood count number  reacts to the treatment and medication (RBCs and WBCs count).
  • To monitor your medical condition: If you are suffering from a medical condition that affects your RBCs, your doctor will recommend a CBC to monitor your blood cell count. This will help managing the condition with proper medication or diet.

What Does a CBC Measure?

A Complete Blood Count measures the levels of the following:

  • WBC or White Blood Cells: These are the cells that build up the immune system of the body and help fight off the germs in your body. But if your white blood cell count is high, then this could be a sign of inflammation, a reaction to medical treatment or condition, or just an infection. When your white blood cell count is low, then this will put you at a higher risk of attracting an infection, indicating your immune system is weak.
  • RBC or Red Blood Cells: These cells are responsible for the transportation of oxygen throughout your body. They also help to carry out carbon dioxide. A low red blood cell count is often the sign of anemia or some other underlying medical condition.
  • MCV or Mean Corpuscular Volume: This is the scale to measure the size of your RBC or red blood cells. The size of these cells tells a lot about the medical condition of the patient. If the cells are larger than normal, then your MCV will be higher, which could be a sign of low vitamin B12 or folate levels. If the size is smaller, then this could be a sign of anemia.
  • Hemoglobin: The protein that holds oxygen in your blood is known as hemoglobin. The blood test determines the Hb level of the patient as well as blood glucose level that is known as HbA1C to ensure if the patient is not suffering from pre-diabetic conditions.
  • Hematocrit: This lets the doctors know how much of your blood contains red blood cells. If the percentage is low, then this could mean iron deficiency. Iron is the mineral that helps keep the red blood cell count high. But, if you have a high score, then this could mean that you are either dehydrated or suffering from some other medical condition or a disorder.
  • Platelets: These help forming  blood clots when there is damage or injury. If the platelet count is low, it is called thrombocytopenia, or if it is higher, it is called thrombocytosis

How to Prepare for a CBC? 

There is nothing special needed to be done prior to the test. It is a simple blood test, but in some cases, the doctor might ask you to fast, so it’s necessary to ask your doctor regarding it. This will mostly be done in the morning, so the doctor might ask you to come for the test on an empty stomach. In very rare cases, the doctors provide special instructions on how the test will be conducted.

What does the CBC Result Indicate? 

When you get a CBC done, your report will have two columns. One will be your result, and the other will be a “reference range.” This reference range is considered normal by doctors and the medical community, and your result will be compared to it to understand your reports better. The higher or lower your result when compared to the reference range the doctor will provide you with proper assessment and plan for the same. 

In many cases, mild anemia is the cause of a difference in the reference range and your result. Be aware that each lab has a different reference range and how they compare the two. Different factors can easily affect your blood. These factors include your age, sex, as well as height above sea level.

Complete Blood Count General Reference Range

White blood cells4,500 to 11,000 cells per microliter
Red blood cells4.7-6.1  million cells/mcL4.2-5.4  million cells/mcL
Hematocrit40.7% to 50.3% 36.1% to 44.3%
Hemoglobin13.5  to 17.5 grams per deciliter12.3 to 15.3 gm/dL
Mean corpuscular volume80 to 96
Platelets150,000 to 350,000 platelets/mcL

Additional tests 

A CBC is never taken as a definitive diagnostic tool. It only helps the doctor to understand the levels of certain blood cells. If a person is being treated for a specific condition, a CBC test usually followed up with other tests that help with the diagnosis of that condition. Your doctor will suggest the required tests based on your CBC report.

Additional tests are also suggested when a healthy person’s CBC results are not normal according to the reference range. The doctor will prescribe a few more tests to understand the person’s health status including CMP, lipid panel or TSH. A CBC may also be done before a treatment is recommended to help understand how your body might react to it.


A CBC is useful to evaluate the overall health status of a person. There are very low to absolutely no risks associated with a CBC test. The blood test only involves taking a sample of blood from the patient. The reports of this blood test can be used to decide the further course of treatment.

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Frequently Asked Questions (FAQs)

Can you have alcohol the night before a CBC test?

It is advised to stay away from alcohol before undergoing a CBC test. It will help doctors identify underlying issues better.

How long does it take to get a CBC test result?

It takes around 24 hours for your doctor to receive the test results of a CBC test. 

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At Apollo, we believe that easily accessible, reliable health information can make managing health conditions an empowering experience. AskApollo Online Health Library team consists of medical experts who create curated peer-reviewed medical content that is regularly updated and is easy-to-understand.

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