What is blood count?

The blood count test (CBC) is one of the most common basic clinical laboratory tests to count blood cells present in the blood (such as that of red blood cells, white blood cells, and platelets) suspended in the liquid part of the blood (plasma). This is because it allows us to gather a lot of data from various components of the examination. This test is often done as part of a routine physical examination. It can provide valuable information about the blood and blood-forming tissues, especially those in the bone marrow of a patient, as well as other body systems.

The test may include:

  • Hematocrit: percentage of total blood part corpuscular, consisting mainly of red blood cells.
  • Hemoglobin: protein found in the red blood cells, charged with the transportation of oxygen to the body.
  • Red blood cells
  • Mean corpuscular volume of red blood cells.
  • Average content of hemoglobin in red blood cells (MCH).
  • Average concentration of hemoglobin in red blood cells (MCHC).
  • Distribution of the volume of red blood cells (RDW).
  • White blood cells (or leukocytes): the white cell differential measure between the number and percentage of neutrophils, lymphocytes, eosinophils, and basophils.
  • Platelets


Why measure the blood count?

In one drawing, the exam allows us to have a complete blood count, which is actually a series of tests in which the numbers of red blood cells, white blood cells, and platelets in a given volume of blood are counted, and many important parameters from the amount of cells present in the blood. The CBC also measures the hemoglobin content and the packed cell volume (hematocrit) of the red blood cells, assesses the size and shape of the red blood cells, and determines the types and percentages of white blood cells. Components of the complete blood count (hemoglobin, hematocrit, white blood cells, platelets, etc.) can also be tested separately, and are sometimes done that way when a doctor wants to monitor a specific condition, such as the white cell count of a patient diagnosed with leukemia, or the hemoglobin of a patient who has recently received a blood transfusion. Because of its value, though, as an indicator of a person's overall health, the CBC package is most frequently ordered.

Blood count varies in value, due to age and sex. The normal red blood cell count ranges from 4.2 to 5.4 million red blood cells per microliter of blood for men and 3.6 to 5.0 million red blood cells for women.


Standard of preparation

Sampling is usually done in the morning in the hospital. There are no special preparations needed for this test. The doctor will advise and recommend if you need to be fasting prior to the blood examination. You should inform your doctor of any medication you are taking prior to the exam, as some medical treatments may interfere with the blood results.


Is the examination painful or dangerous?

The examination is neither painful nor dangerous. The patient may feel a tingling sensation with the entrance of the needle in the arm when blood is being extracted for examination.


How is the exam performed?

The exam consists of a simple blood sample test.