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Complete blood count (CBC) Test: How to interpret the results

A complete blood count is a blood test that evaluates the cells that are a part of blood, such as leukocytes, known as white blood cells, red blood cells, also called erythrocytes, and platelets.

The part of the CBC that analyzes red blood cells is called a erythrogram, which, in addition to indicating the amount of blood cells, indicates the quality of the red blood cells, whether they are the appropriate size or in the recommended amounts of hemoglobin inside them, which can helps to clarify causes of anemia, for example. This information is provided by the hematimetric indices, which are MCH, VCM, MCHC, and RDW.

Fasting is not necessary for its collection, however, it is recommended you not perform physical activity 24 hours before the exam and you should not consume alcohol in the 48 hours leading up to the test, as this may alter the result.

Complete blood count (CBC) Test: How to interpret the results


A CBC can aid in the diagnosis and monitor the evolution of diseases that can cause changes in the blood, such as:

  • Anemia;
  • Bone marrow disorders;
  • Bacterial, fungal or viral infections;
  • Inflammations;
  • Cancer, especially leukemias or lymphomas;
  • Changes in platelets, such as their increase (platelet) or decrease (platelet);
  • Monitoring of situations that may compromise the functioning of the bone marrow, such as during chemotherapy, for example.

In addition, the blood count is useful for monitoring chronic diseases that may develop with anemia, such as kidney failure, rheumatoid arthritis, heart failure or lung disease, for example.

How is it done

The examination is performed automatically using flow cytometry equipment, which has the function of counting, evaluating and classifying blood cells according to various established criteria.

However, even with the result provided by the equipment, a microscopic analysis, called a blood smear differential count, must be performed by a qualified Clinical Analyzer. Differential counting consists of leukocyte differentiation and visualization of structures present in red blood cells or leukocytes. In addition, counting under the microscope allows the identification of immature cells and thus may aid in the diagnosis of leukemia, for example.

How to interpret a CBC

In order to interpret the blood count, the physician must observe the results and verify if the values are normal, high or low, and correlate them with possible symptoms you present and the result of other tests that may have been requested.

If you have recently done a blood count and want to understand what the result may mean, enter your details below:

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Some situations that can be observed in a blood count are:

1. Red blood cells or erythrocytes

Complete blood count (CBC) Test: How to interpret the results

The erythrogram is a part of the CBC in which the characteristics of red blood cells, also known as erythrocytes, are analyzed.

HT or HCT - Hematocrit

Represents the percentage of the volume occupied by red blood cells in the total volume of your blood blood volume.

High: Dehydration, polycythemia and shock;

Low: Anemia, excessive blood loss, kidney disease, iron and protein deficiency, and sepsis.

Hb - HemoglobinIt is one of the components of red blood cells and is responsible for oxygen transport.

High: Polycythemia, heart failure, lung disease, and high altitude;

Low: Pregnancy, iron deficiency anemia, megaloblastic anemia, thalassemia, cancer, malnutrition, liver disease and lupus.

In addition to the amount of red blood cells, a blood count should also analyze their morphological characteristics, as they may also indicate diseases. This assessment is done using the following hematimetric indices:

  • MCV or Average Corpuscular Volume: Measures the size of red blood cells, which may be increased in some types of anemia, such as vitamin B12 or folic acid deficiency, alcoholism, or bone marrow changes. If it is decreased, it may indicate iron deficiency or genetic anemia, such as Thalassemia;
  • MCH or Mean Corpuscular Hemoglobin: indicates the total hemoglobin concentration by analyzing the size and color of the red blood cells. See what can high or low levels of MCH indicate
  • MCHC (mean corpuscular hemoglobin concentration): shows the concentration of hemoglobin by red blood cells, which is usually decreased in anemia, being called hypochromia;
  • RDW (Range of Red Blood Distribution): This is an index that indicates the percentage of size variation between red blood cells in a blood sample, so if there are red blood cells of varying size in the sample, the test may be altered, which may be a clue to the onset of iron or vitamin deficiency anemia, for example, and their baseline values ​​are between 10 and 15 percent. 

2. White blood cells (Leukocytes)

Complete blood count (CBC) Test: How to interpret the results

A white blood count is an important test to help verify a person's immunity and how the body can respond to different situations, such as infections and inflammation, for example. When the concentration of leukocytes is high, the condition is called leukocytosis, and if there is a low count, it is called leukopenia. See how to understand the result of white blood cells.


High: Infections, inflammation, cancer, trauma, stress, diabetes or gout.

Low: Lack of vitamin B12, sickle cell anemia, steroid use, post-surgery or thrombocytopenic purpura.


High: Allergy, worms, pernicious anemia, ulcerative colitis or Hodgkin's disease.

Low: Use of beta-blockers, corticosteroids, stress, bacterial or viral infections.


High: After spleen removal, chronic myeloid leukemia, polycythemia, chicken pox, or Hodgkin's disease.

Low: Hyperthyroidism, acute infections, pregnancy or anaphylactic shock.


High: Infectious mononucleosis, mumps, measles and acute infections.

Low: Infection or malnutrition.


High: Monocytic leukemia, lipid storage disease, protozoan infection or chronic ulcerative colitis.

Low: Aplastic anemia.

3. Platelets

Platelets are actually fragments of cells that are very important because they are responsible for initiating the coagulation process. Normal platelet reference range should be between 150,000 to 450,000 / mm³ of blood.

Elevated platelets are of concern as they can cause blood clots and thrombi, with risk of thrombosis and pulmonary embolism, for example. When reduced, they can increase the risk of bleeding. 

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