• Post last modified:December 31, 2022
  • Reading time:10 mins read

The complete blood count (CBC) test is the counting of the cells that are present in the blood, including red blood cells (RBCs), white blood cells (WBCs), and platelets (PLTs). Also the shape, size, and concentration of these cells in the blood.

So the CBC is a group of tests that can evaluate a patient’s overall health status. The number of blood cells can be lower or higher in a variety of diseases and conditions such as infections, injury, anemia, or leukemia.

What are the blood cells:

Composition of the Blood

The average adult has a blood volume of roughly 5 liters, which is composed of plasma (55%) and several kinds of cells (45%).

Plasma is a fluid composed of 90 – 92% of water and 8 – 10% of proteins and it is a pale yellow but transparent and clear fluid.

Cells include RBC (red blood cell), WBC (white blood cells), and Platelets.

Red Blood Cells

Red blood cells (RBCs) also called erythrocytes, are produced in the bone marrow and released in the blood. Every RBC contains hemoglobin, an iron-containing complex protein that carries oxygen from the lungs throughout the whole body.

White Blood Cells

White blood cells also called leukocytes, are colorless, that lack hemoglobin. Every day we encounter millions of microorganisms that may cause infections but these WBCs in our blood are involved in protecting our body against infections and have a role in inflammation and allergic reactions.

There are five different types of WBCs i.e., Neutrophils, Eosinophils, Basophils, Lymphocytes, and Monocytes and each has a different function.


Platelets, also called thrombocytes, are tiny cell fragments that circulate in the bloodstream and are essential for normal blood clotting.

Blood clotting, or coagulation, is an important process that prevents excessive bleeding when a blood vessel is injured. Platelets adhere to the injury site and clump together to form a wall-like structure and prevent blood loss.

The Tests Included in CBC

A complete blood count includes red blood cell (RBC) count, white blood cell (WBC) count, hemoglobin estimation, platelet count, as well as hematocrit levels.

Red blood cell (RBC) tests

  • RBC count: Counting the actual number of red blood cells per microliter (cells/mcL) of your blood
  • Hemoglobin estimation: The total amount of hemoglobin (in grams) per deciliter of whole blood (grams/deciliter)
  • Hematocrit: The percentage of your whole blood volume that contains red blood cells.
  • RDW: RBC distribution width is the variation in the size of the red blood cells
  • MCV: Mean corpuscular volume is the measurement of the average size of the RBC.
  • MCH: Mean corpuscular hemoglobin is the average amount of hemoglobin inside your red blood cells.
  • MCHC: Mean corpuscular hemoglobin concentrations are the average hemoglobin concentration inside your red blood cells.

The White Blood Cells (WBC) tests

TLC: The counting of the total number of white blood cells present per microliter of your whole blood.

DLC: Differential leukocyte count is counting the absolute number and the percentage of five types of WBCs present in the blood i.e., Neutrophils, Eosinophils, Basophils, Lymphocytes, and monocytes.

Platelets test:

The total number of platelets present per microliter of your blood.

  • PDW: Platelet distribution width is the variation in the size of the platelets.
  • MPV: Mean platelet volume is the measurement of the average size of the RBC.
  • Large platelet cell ratio
  • Platelet criteria

How CBC (Complete blood count) Test is Done?

CBC is performed by a qualified Lab technician in the medical lab using an automated Hematology analyzer. The hematology analyzer measures various parameters of blood, including cell counts and the physical features of the cells.


Hematology analyzer, Rotor, Gloves, Blood Sample (2 ml) in an EDTA vail.

Also read: Blood Collection Technique

Principle of Hematology Analyzer

The working principle of early hematology analyzers was based on Coulter’s Principle. However, they have evolved to encompass numerous techniques such as Flow Cytometry, & Spectrophotometry.

The Procedure of CBC Test:

  1. Collect about 2 ml of the blood sample in a lavender top tube (EDTA vail).
  2. Shake the tube softly and make sure the blood is mixed well with EDTA in the vail to avoid clotting.
  3. Turn “ON” the rotor.
  4. Put the vail on the rotor to mix the blood sample with the anticoagulant.
  5. Turn “ON” the hematology analyzer.
  6. Click on the new sample.
  7. Click on ID 1, and type the unique ID of the sample and click OK.
  8. And then, click on ID 2 and type the name of the patient and click OK.
  9. Then introduce the blood sample to the hematology analyzer (CBC machine).
  10. After waiting for 1-2 minutes, the result will be displayed on the screen.
  11. Now print the result, and turn off the machine.

CBC Test Result:

NameNormal Range
RBC3.50 – 5.50
MCV75.0 – 100.0
RDW%11.0% – 16.0%
RDWa30.0 – 150.0
HCT35.0 – 55.0
PLT100 – 350
MPV8 – 11
PDW0.1 – 99.9
PCT0.01 – 9.99
LPCR0.1 – 99.9
WBC4.0 – 11.0
HGB11.5 – 16.5
MCH25.0 – 35.0
MCHC31.0 – 38.0
LYM0.5 – 5.0
GRAN1.2 – 8.0
MID0.1 – 1.5
LYM%15.0 – 80.0
GRA%35.0 – 80.0
MID%2.0 – 15.0

CBC Test Clinical significance

  • A high WBC count (leukocytosis) may signify an underlying malignancy.
  • A low WBC count (leukopenia) may point toward a bone marrow problem or related to some medications, such as chemotherapy
  • A low red blood cell count or hemoglobin may suggest anemia, which can have many causes. Possible causes of high red blood cell count or hemoglobin (erythrocytosis) may include bone marrow disease or low blood oxygen levels (hypoxia).
  • A low platelet count (thrombocytopenia) may be the cause of prolonged bleeding or other medical conditions that affect the production of platelets in the bone marrow.
  • A high platelet count (thrombocytosis) may point toward a bone marrow problem or severe inflammation.
  • The usual range of the blood cell count varies in males and females or different age groups of the persons.
  • The blood cell count varies in the pregnant female.