FBC: understand the reference values

Complete blood count : what it is for and reference values

The tests help to assess health and are an important tool for the diagnosis of some changes and diseases. The blood count , for example, is a good example of this.

It can be used to detect some specific conditions, such as anemia , but it can also be indicative of other conditions, which are confirmed with complementary tests.


What is a complete blood count?

A complete blood count is a type of blood test done to measure the overall health of the body. It is widely used to diagnose disorders such as anemia , autoimmune diseases and leukemia . The test consists of measuring the levels of red blood cells (red blood cells), white blood cells (leukocytes) and platelets.

It is one of the types of blood tests most requested by doctors in routine examinations. This is because it assesses health in general, calculating the quantity and shape of the three types of basic cells present in the blood.

The reference values ​​for the blood count were established in the 1960s, based on the values ​​present in 95% of the healthy world population. However, about 5% of people without health problems may have levels that are out of step with the reference.

Thus, small variations, more or less, do not exactly mean the presence of some disease. Thus, the results should always be evaluated by specialists, taking into account the general clinical picture.

What are the basic cells present in the blood?

The cells analyzed by the blood count are the three main ones present in the blood, they are:

  • Red blood cells : red blood cells, responsible for transporting oxygen through the body;
  • Leukocytes : white blood cells, responsible for the body’s defense system, help fight infections;
  • Platelets : fragments of cells that are produced in the bone marrow, responsible for blood clotting.

How is the blood count done?

The blood test is done in a hospital or laboratory by nursing professionals. Its performance is similar to any other type of blood test.

Generally, the person sits and the tourniquet (elastic) is attached to his / her arm to interrupt blood flow. Thus, the veins become wider and more apparent, which facilitates the collection. Asepsis is performed (cleaning that eliminates possible microorganisms) of the area of ​​the arm to be pierced and a needle pierces the patient’s vein.

Blood is collected in the syringe or tube. Then the rubber band is removed and gauze is pressed to prevent bleeding. As soon as the gauze is removed, a bandage is placed.

When should the blood count be done?

The blood count is usually ordered as a routine exam to check the overall health of the organism. It can be done as part of the medical follow-up, every 6 months or according to medical advice.

However, you may also be asked to diagnose a specific condition, such as asthma . Or, it is useful to assess the causes of some symptoms. For example, it is common for patients to experience extreme tiredness when they have anemia. Thus, the blood count helps to confirm or rule out possible changes.

In addition, the test can also be done to check whether the body is responding well to drug or radiation treatment, whether cell values ​​are normal, before surgery or to analyze the amount of blood lost in a hemorrhage.

Can pregnant women do the blood count?

Yea! There is no contraindication for this test, as it is done only with blood collection. Therefore, anyone can do it, including pregnant women.

How to prepare and what care after a blood count?

In general, it is recommended that the last meal be eaten between 8 and 12 hours before the blood count. In addition, it may be ideal to avoid extensive physical exercise and alcoholic beverages within 48 hours before the exam.

Some tests involving the use of iodine or contrast can affect the result, but it is common for the laboratory itself to provide guidance on this.

Altered FBC results: what can they indicate?

The complete blood count always comes with a reference table given by the laboratory itself. This is important, as values ​​may vary. However, identifying a change does not mean that something is wrong.

As it is a complex exam, with several evaluations, the results cannot be analyzed in isolation. That is, each value needs to be considered in relation to the other results, as well as the clinical condition of each patient.

The test is performed in three stages, called erythrogram , leukogram and platelets . Such steps analyze the following characteristics:

  • Leukocyte count: neutrophils, lymphocytes, monocytes and basophils;
  • Red blood cell count;
  • Hemoglobin;
  • Hematocrit;
  • VGM (Average Corpuscular Volume);
  • HGM (Average Corpuscular Hemoglobin);
  • CHCM concentration (mean corpuscular hemoglobin concentration);
  • RDW;
  • Platelet Count;
  • MPV.


It is the first step of exam analysis, in which the values ​​of red blood cells are analyzed.

Red Cells

Low red blood cell values ​​may indicate cases of normocytic anemia, a type that has normal-sized red blood cells with little cell production.

Possible causes include:

  • Trauma;
  • Enzymatic deficiencies;
  • Nutritional deficiency
  • Bone marrow injuries;
  • Chronic inflammatory diseases.

High values ​​are called erythrocytosis and can mean polycythemia, the opposite of anemia. In this case, the thickness of the blood may increase, reducing the speed of circulation. Possible causes include:

  • Polycythemia vera;
  • Water loss;
  • Tumors producing erythropoietin.


Hemoglobin is a protein present in red blood cells, responsible for pigmenting the blood and transporting oxygen throughout the body. When your values ​​are low, the causes can be:

  • Cirrhosis;
  • Leukemia;
  • Renal insufficiency;
  • Porphyria;
  • Bleeding;
  • Iron and vitamin deficiency;
  • Use of some medications, such as for the treatment of AIDS and cancer

High values ​​can be caused by conditions such as:

  • Dehydration;
  • Pulmonary emphysema;
  • Polycythemia;
  • Kidney tumor;
  • Tobacco use;
  • Use of anabolic steroids.


Hematocrit represents the percentage of blood occupied by red blood cells, for example, if it appears as 40%, it means that 40% of the patient’s blood is composed of red blood cells.

When the hematocrit is low, it is usually an indication of a change in the amount of red blood cells or hemoglobin. Possible causes include:

  • Anemia;
  • Bleeding;
  • Leukemia;
  • Malnutrition;
  • Lack of vitamin B12, iron or folic acid.

High values ​​indicate an increase in the amount of red blood cells and hemoglobin in the blood. In general, this picture can be related to dehydration, but it can also include:

  • Lung diseases;
  • Congenital heart disease;
  • Polycythemia;
  • Low concentration of oxygen in the blood.


It assists in the analysis of the size of red blood cells and allows the diagnosis of anemia.

High CMV is an indication that red blood cells are larger than normal (macrocytic red blood cells). In such cases, the causes can be:

  • Megaloblastic anemia;
  • Pernicious anemia;
  • Excessive consumption of alcohol;
  • Myelodysplastic syndromes;
  • Hypothyroidism;
  • Hemorrhages.

Low MCV values ​​indicate that red blood cells are smaller than normal (microcytic red blood cells). Possible causes include:

  • Anemia due to lack of iron;
  • Uremia;
  • Chronic infections;
  • Minor thalassemia.


Elevated HCM values ​​indicate that hemoglobin is higher within red blood cells, making it darker (a condition called hyperchromia). Possible causes include:

  • Chronic liver disease;
  • Deficiency of folic acid.
  • Excessive consumption of alcohol;
  • Vitamin B12 deficiency;
  • Myelodysplasia;
  • Spherocytosis;
  • Hypothyroidism.

When the HCM is low, it is indicated that there is less hemoglobin within the red blood cells, so that they become clearer (a condition called hypochromia). Possible causes include:

  • Rheumatoid arthritis;
  • Iron deficiency anemia;
  • Sickle cell anemia;
  • Sideroblastic anemia;
  • Thalassemia.


CHCM is the average hemoglobin concentration in red blood cells. In the results, it can appear as hypochromic, indicating little hemoglobin in the red blood cells, and possible causes include:

  • Anemias;
  • Cirrhosis;
  • Leukemia;;
  • Renal insufficiency;
  • Hypothyroidism;
  • Blood clotting disorders;
  • Use of some medications, such as for AIDS treatment.

When CHCM is elevated, it is called hyperchromic, indicating hemoglobin levels beyond normal. The most common possible cases include:

  • Excessive consumption of alcohol;
  • Thyroid changes.


RDW is an index that assesses the difference in size between red blood cells. When elevated it can mean a problem in the morphology of these cells.

Its high value may appear, for example, due to iron deficiency, because the lack of this element prevents the formation of hemoglobin in a normal way, reducing the size of the red blood cell.

When the results are low, the possible causes may be some chronic disease, such as liver disease or kidney problems.


The second stage of analysis of the exam represents the values ​​of white blood cells.


High leukocyte values ​​are called leukocytosis and usually represent an infection. Extremely high levels can indicate leukemia and, in these cases, the values ​​exceed 50 thousand cells / mm 3 .

Low values, on the other hand, a condition called leukopenia, may indicate bone marrow depression , caused by a viral infection or toxic reactions.

Divided into five types in the blood count, the leukocyte values ​​help to understand and diagnose infectious and hematological diseases. Its types are:

  • Basophils : found only up to 1% in patients considered healthy, above this value may indicate allergic processes;
  • Eosinophils : when their values ​​are high, it indicates cases of allergic processes or parasitosis;
  • Neutrophils : most found in adults, its high value may indicate bacterial or viral infections;
  • Lymphocytes : predominant in children, when it is present, at a high level, in adults, it may indicate viral infections or, in rarer cases, leukemia. This cell can be affected by the HIV virus, which is why AIDS causes immunosuppression (weakening of the immune system);
  • Monocytes : their high values ​​indicate viral infections, but their level may increase after chemotherapy.

Read more: Tall eosinophils: what does it mean?


Platelets, as previously explained, are fragments of cells responsible for blood clotting. When tissue is injured, platelets are routed to the site of the injury, grouping together as a form of tampon, which allows the wound to remain watertight without losing a lot of blood.

Platelet values ​​far below normal, called thrombocytopenia , may represent a risk of death, since the patient is susceptible to spontaneous bleeding. Its high values ​​are called thrombocytosis.

The values ​​considered normal vary between 150 and 450 thousand per microliter, but with values ​​close to 50 thousand, the organism does not present difficulties in initiating coagulation.

What are the reference values ​​for the complete blood count?

The reference values ​​of each cell analyzed can vary from laboratory to laboratory, despite being close values. Generally, the values ​​that were considered normal will appear in the result, along with the values ​​intended for the patient.

However, the following values ​​of:

Erythrocytes, hemoglobin and hematocrit

The reference values ​​are usually:

Erythrocytes (million / mm³)Hemoglobin (g / 100mL)Hematocrit (%)
Newborns4 – 5.613.5 – 19.644 – 62
Children (3 months)4.5 – 4.79.5 – 12.532 – 44
Children (1 year)4 – 4.711 – 1336 – 44
Children (10 to 12 years)4.5 – 4.711.5 – 14.837 – 44
Women (pregnant women)3.9 – 5.611.5 – 1634 – 47
Women4 – 5.612 – 16.535 – 47
Men4.5 – 6.513.5 – 1840 – 54

Mean corpuscular volume (VCM), mean corpuscular hemoglobin (HCM) and concentration of corpuscular hemoglobin (CHbCM)

The values ​​in general are:

AgeVCM (µ³)HbCM (pg)CHbCM (%)
Children (3 months)83 – 11024 – 3427 – 34
Children (1 year)77 – 10123 – 3128 – 33
Children (10 to 12 years)77 – 9524 – 3030 – 33
Women81 – 10127 – 3431.5 – 36
Men82 – 10127 – 3431.5 – 36


On average, the platelet reference is:

150,000 to 400,000 (µl)

White series or leukocytes

The white series, or also leukocytes, has the following reference values:

Total leukocytes4,000mm³ – 10,000mm³
Eosinophils1% – 5%
Basophils0% – 2%
Lymphocytes20% – 40%
Monocytes2% – 10%
Neutrophils45% -75%

CBC risks

The risks of a complete blood count are almost nonexistent and extremely rare. In healthy people, a hematoma may remain in the region where the blood was collected and, in some cases, the vein may also become swollen. To reduce swelling, simply make cold compresses several times a day.

If the patient uses anticoagulant medications or has clotting problems, continuous bleeding may occur after collection. In such cases, the health professional must be advised prior to the examination.

Price: how much does the complete blood count cost?

The complete blood count exam can be done in private clinics or by SUS. In the first case, the private exam is in the range of R $ 40 to R $ 70, and may vary depending on the region and laboratory. Patients can take the exam through popular price programs, which give discounts that can reach half the value.

Health plans usually cover the exam, but it can also be done by SUS, free of charge. In the latter case, it is necessary to have a request from a SUS doctor.