Complete blood count (CBC) refers to a kind of blood test prescribed to evaluate overall health and detect disorders like leukemia, anemia, and other infections. Typically, your attending doctor would like to determine the Mean Corpuscular Hemoglobin or MCH level in blood along with other findings. Primarily, CBC works to measure several different components of blood that include:

Red blood cells (RBC), responsible for carrying oxygen which carries oxygen
White blood cells (WBC) that function to fight infections
Platelets that prevent blood clotting
Hemoglobin, a protein that carries oxygen in RBC’s. 
Hematocrit, the proportion of RBC compared to the fluid component, and or plasma within the blood.

As such, any abnormal increase or decrease in the cell count revealed in a CBC test may indicate an underlying disease. 

Why CBC is done 

Your doctor might prescribe a CBC for quite a few reasons like: 

Review of general health – CBC can be recommended as a part of routine medical checkup to help monitor health problems and act as a screening test for disorders like anemia, leukemia, etc. 

In-depth diagnosis for a medical condition –Any patient experiencing sudden fatigue, uneasiness, weakness, fever, bleeding, bruising, or infection can be recommended to undergo a CBC test. It helps in diagnosing early symptoms for any critical disease. 

Monitoring a sustaining medical condition –Any disorders resulting out of blood disorders can be determined through a CBC test. In some instances, some patients witness low blood cell count as an effect of a particular drug. In such cases, a CBC is the first approach towards treating the condition.

How to be ready for the test 

In case your blood sample is being tested for CBC; specifically, one is allowed to eat and drink normally. However, if the blood sample is to be tested for additional diagnosis, your doctor might recommend fasting depending upon your medical condition and case history.
What to expect 

To perform a CBC, you will be required to give your blood sample usually taken at the diagnostic center by medical staff. The process involves inserting a needle to extract blood from your vein, often at the point where your elbow bends. Further, the collected blood sample is taken to the lab for analysis, and one is free to continue with his daily activities.


Here’s how an average CBC test result look like for an adult under normal conditions: 

Red blood cell count

Male: 4.35-5.65 trillion cells/L*

(4.32-5.72 million cells/mcL**)

Female: 3.92-5.13 trillion cells/L

(3.90-5.03 million cells/mcL)


Male: 13.2-16.6 grams/dL***

(132-166 grams/L)

Female: 11.6-15 grams/dL

(116-150 grams/L)


Male: 38.3-48.6 percent

Female: 35.5-44.9 percent

White blood cell count

3.4-9.6 billion cells/L

(3,400 to 9,600 cells/mcL)

Platelet count

Male: 135-317 billion/L

(135,000 to 317,000/mcL)

Female: 157-371 billion/L



* L = liter, ** mcL = microliter, *** dL = deciliter Why CBC is never a definitive test 

Why CBC is never a definitive test 

Although CBC can be the determining test for several diseases, it can never be considered as a definitive test. Depending on the reason why your doctor prescribed the test, any result of CVC that falls right under the normal range might or might not require to follow up. However, CVC, along with the results from other tests, can be the determining factor to carry further diagnosis and treatment options as deemed necessary by the attending doctor. For any individual, whose test results fall a little outside the normal range for blood count may not be an alarming issue, unless he has any persisting illness of any kind. In some instances of cancer treatment, CBC test results were witnessed to rest right outside the normal range, thus pushing the doctors to change the treatment plan. Since a CBC test is mainly concerned with blood, any patient who shows moderate to high deviation from the normal range needs to be referred to a hematologist. 

What could the CBC results possibly indicate?

CBC test is mainly concerned with the count of three components of blood, namely RBC, hematocrit, and hemoglobin. As such, any measure of these components when it goes lower than the accepted range, it is most likely a determining factor for anemia, leading to weakness and fatigue in tandem. Additionally, anemia occurs due to quite a few reasons, including iron deficiency in the blood, blood loss, or any other undefined condition.

Low RBC count, also known as Erythrocytosis along with lower levels of either hemoglobin or hematocrit, could lead to moderate to severe heart disease. 

On the other hand, a low white blood cell count called leucopenia is often a medically induced condition arising out of autoimmune disorders that causes issues with WBC and bone marrows.  Quite a few numbers of medications can also affect to bring down the white blood cells to lower its counts at a drastic rate. On the flip side, when your WBC count is high, it is suggestive that the patient has inflammation or any infection. Additionally, it could also be one is suffering from acute immune system disorder or an issue with bone marrow. High WBC could also be a reaction to some regular medication. 

In case of platelet count, something lower than the normal range is known as Thrombocytopenia, or when much higher, called Thrombocytosis signals an underlying condition. Alternately, a side effect from a prolonged medication can also be the cause of low platelet count.