Blood count - Hemochromocytometric examination

Generality

HEMOCROM is one of the most requested blood tests, as its results help to keep the general health of a person under control.

• Number of all blood cells, ie red blood cells (erythrocytes), white blood cells (leukocytes) and platelets (thrombocytes);
• Leukocyte formula, ie the percentage of different types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils and basophils;
• Proportion of blood volume occupied by erythrocytes ( hematocrit );
• Analysis of the physical characteristics (shape and size) of red blood cells and platelets, indicated by parameters such as:
• MCV (measure of the average size of red blood cells);
• MCH (average hemoglobin content in red blood cells);
• MCHC (average hemoglobin concentration in red blood cells);
• RDW (variability in the size of red blood cells);
• MPV (measure of the average size of a plate).

What's this

The blood count is an exam that can provide the doctor with important indications concerning the corpuscular part of the blood, that is the one occupied by white blood cells (GB), red blood cells (GR) and platelets (PLT). These cells are produced in the bone marrow and, when mature, are released into the bloodstream.

Usually, blood counts are performed using automated instruments that measure various parameters, including counting the various types of cells present in the analyzed blood sample. The exam also provides an indication of the physical characteristics of some of these elements.

A standard blood count therefore includes:

• Evaluation of red blood cells (or erythrocytes) : they represent the most numerous blood cells. The erythrocytes have the shape of a biconcave disk (slightly flattened in the center) and have a characteristic red color (hence the name) due to their hemoglobin content (iron-containing protein, necessary to transport oxygen in the blood).

  Red blood cells live on average 120 days in the circulatory system and are subsequently removed in the spleen; for this reason, the bone marrow must produce new ones continuously, in order to replace dead, destroyed or lost elements during bleeding.

  The evaluation of red blood cells in the blood count includes: GR counts, hemoglobin (Hb), hematocrit (Hct) and erythrocyte indices, which include the mean corpuscular volume (MCV), the corpuscular hemoglobin average (MCH), the average hemoglobin concentration in corpuscles (MCHC), and, sometimes, the amplitude of erythrocyte distribution (RDW). Blood counts may or may not include reticulocyte counts (precursors of mature red blood cells).

• Evaluation of white blood cells (or leukocytes) : these cellular elements of the blood are responsible for defending the body against infectious agents, foreign substances and other causes of damage. Leukocytes also play an important role in allergies and inflammation.

  White blood cells are divided into two subgroups: granulocytes (eosinophils, neutrophils and basophils) and mononuclear cells (lymphocytes and monocytes).

  The white blood cell count (evaluation of the total number of leukocytes present in the blood sample) is part of the blood count. These cells are present in the blood in a relatively constant amount; their number may increase or decrease temporarily, depending on what happens in the body.

  Blood counts may or may not include the differential white blood cell count ( leukocyte formula ). This information identifies and counts the number of the various types of leukocytes present and serves to understand whether an infection, an allergy or a strong stress reaction is in the body. In some pathologies, such as leukemia, abnormal white blood cells (immature or mature) multiply rapidly, increasing their overall count.

• Evaluation of platelets (or thrombocytes) : they are the smallest blood cells; they take the form of small disks and are produced by the bone marrow. Platelets have an average life of 10 days and play an important role in blood clotting.

  Following traumas or small lesions in the walls of blood vessels, thrombocytes are transported to the area affected by the blood and stick along the edges of the wound, progressively blocking the bleeding. Their possible alterations can increase the risk of excessive bleeding or predispose to the formation of ecchymoses.

  In the blood count, these cell types are generally counted; the evaluation can include or not the mean platelet volume (MPV) and / or the amplitude of the platelet distribution (PDW).

Why do you measure

The blood count serves to assess the general state of health and allows us to suspect or establish the presence of certain diseases. Therefore, this test is prescribed as a routine examination for healthy subjects, but also for the diagnosis or monitoring of various conditions and diseases that affect blood cells, such as: anemia, recurrent infections, inflammation, coagulation disorders or tumors. In this way, the doctor can ascertain his suspicions and possibly prescribe more targeted tests to define a precise clinical picture.

The blood count is also used to monitor the pathology and / or the effectiveness of the treatments, after the diagnosis has been established.

When is the exam indicated?

The blood count is indicated by the doctor in the following cases:

• As part of routine exams;
• When the patient shows signs and symptoms that may be related to diseases that affect blood cells;
• For monitoring on a regular basis of pathological conditions or therapeutic regimens (especially if they damage blood cells, such as chemotherapy or radiotherapy).

Significant abnormalities of one or more blood cell populations may indicate the presence of one or more pathologies. Usually, in these cases, other tests are performed (eg blood smear or bone marrow biopsy) as a support in determining the cause of abnormal blood count results and providing additional information to the doctor.

Normal values

The normal values, in the adult, are shown in the following table:

Hematocrit (Ht)

The hematocrit (Ht, volume of "packed" erythrocytes) expresses the relationship between the total volume of red blood cells and the total volume of blood. This is why it is said to express the volume of "packed" cells.

The hematocrit also gives us a rough idea of ​​the degree of blood density (when it is above the norm, it means that the blood is more viscous, so there is a greater risk of thrombosis).

Hemoglobin (Hb)

Hemoglobin is the most important oxygen transport protein and is located within erythrocytes. It is a red colored pigment.

The normal values ​​for the adult man vary between 13.5 and 18 g / dl (g / dl = grams of hemoglobin on deciliter of blood); in women between 12 and 16 g / dl. Currently, in order to measure it, the laboratories used for the blood cell count, use automatic counters of cells that measure the hemoglobin directly inside the red blood cells.

A person can donate blood only if there is a minimum level of security. These levels, translated into figures, are corresponding to a hemoglobin concentration of about 12.5 g / dl for women, while for men they are 13.3 g / dl.

High Values ​​- Causes

Number of red blood cells (or erythrocytes)

An increase in red blood cells ( polycythemia ) is relatively rare. If the erythrocytes are numerically higher and are smaller than normal, the patient could be affected by Mediterranean anemia.

Among the benign causes of the increase in red blood cells it is necessary to consider:

• Significant dehydration (most often associated with repeated episodes of diarrhea);
• Shortages of oxygen (long stays in the high mountains, smoking etc.);
• In athletes, taking erythropoietin (a hormone that regulates the production of red blood cells by the bone marrow).

Number of white blood cells (or leukocytes) with leukocyte formula

Any infection of the organism, even of modest severity, can cause an overall increase in the number of white blood cells ( leukocytosis ), as well as intense stress and some forms of tumors (leukemia and myeloproliferative disorders).

Leukocytosis may also depend on intense exercise, trauma, burns, inflammatory processes and allergic reactions.

Number of platelets

Thrombocytosis indicates too high a platelet value. This may be due to an infectious disease or surgery.

More rarely, the increase in the number of platelets is the consequence of bone marrow diseases (eg polycythemia, myeloproliferative disorders), inflammatory bowel diseases and various cancer processes.

Hemoglobin concentration and hematocrit

• In general, hemoglobin reflects the result of red blood cell count and hematocrit. If Hb has a high value - a very rare event - it could be associated with fluid loss, respiratory failure or polyglobulia (ie an excessive increase in red blood cells in the blood).
• The hematocrit generally reflects the result of the number of red blood cells; the most common cause of values ​​above the norm is dehydration, but the alteration may also depend on polycythemia vera, acute renal failure and some lung diseases.

Low Values ​​- Causes

Number of red blood cells (or erythrocytes)

If the value of the red blood cells is lower than the normal value and the hemoglobin is reduced, the presence of anemia may be suspected.

A reduction in the number of red blood cells may also depend on:

• Acute or chronic blood loss (for example: gastrointestinal ulcers, hemorrhoids or physiological situations, such as menstruation):
• Hemolysis (eg destruction of blood cells following a post-transfusion immune reaction);
• Nutritional deficiencies (eg iron deficiency anemia, vitamin B12 or folate deficiency, etc.);
• Disorders or bone marrow damage;
• Chronic inflammatory disorders;
• Kidney failure.

Number of white blood cells (or leukocytes) with leukocyte formula

A low number of white blood cells, called leukopenia, can be considered constitutional, within certain limits.

A clear reduction of the leukocytes in the blood count must induce, instead, to carry out a check on the bone marrow function, aimed at excluding pathologies or damage to the bone marrow, infectious diseases or neoplastic processes (eg leukemia, lymphomas or other types of cancer). In other cases, the reduced value of white blood cells may be indicative of viral hepatitis, liver dysfunction, autoimmune reactions or immune system pathologies.

Number of platelets

If the number of platelets is too low ( thrombocytopenia ), there may be a problem with bleeding or early cell death. This condition may depend on infections, use of certain drugs (including acetaminophen, quinine and sulfa drugs), myelodysplasia and autoimmune diseases.

Hemoglobin concentration and hematocrit

Usually, hematocrit and hemoglobin concentration reflect the red blood cell result, providing additional information. The causes range from iron deficiency anemia (from iron deficiency) to bleeding, from prolonged aerobic training to chronic renal failure.

How to measure it

The count of red blood cells, but also of white blood cells and platelets (blood cells), is performed with electronic machines, called contaglobuli, which are based on two principles called impedance and light scattering ("light scattering").

Some parameters are called absolute, or calculated directly by the instrument, while others are derived from absolutes. The former are represented by the number of red blood cells, hemoglobin (Hb), MCV (Mean Cell Volume, or medium globular volume) and Ematocrito (Hct), while derivatives from absolutes are represented by the average cellular content of hemoglobin (mean cell hemoglobin, MCH) and the mean cellular concentration of hemoglobin (mean cell hemoglobin concentration, MCHC).

How to make the withdrawal

• The blood count is performed on a blood sample taken from the vein of an arm; in newborns, even a few blood drops taken with a small needle from the tip of a finger or foot are sufficient.
• Blood is collected in test tubes containing an anticoagulate that keeps the sample liquid.
• To take the sample, the patient must uncover the arm. The operator passes a cotton ball soaked in disinfectant in the area and, after having found the right vein, inserts the needle of a syringe. The patient feels a slight tingling that is bearable for just a few seconds.

Preparation

Fasting is not necessary for taking the blood sample for evaluation of the blood count: the examination takes place on the corpuscular part of the blood, that is on the cells, for which the fact of having taken food or drink has no influence.

However, if in addition to the blood count you have to perform some other test on the plasma that foresees fasting (such as the determination of glycaemia or cholesterol) it will be necessary to go to the laboratory on an empty stomach. The general practitioner who prescribes the analysis will still be able to provide useful information for his case.

Interpretation of Results

The doctor interprets the results of the various components of the whole blood count.

In relation to the objective of the analysis and the suspected cause, other specific investigations can be carried out, such as the blood smear or the complete metabolic panel, to establish the correct diagnosis. Other generic tests may include a bone marrow biopsy, a culture test of the affected area (eg blood culture, urine culture, etc.) and evaluation of inflammation rates (including PCR and ESR).