Complete blood count (clinical analyzes)




The blood count, also called hemogram, is a laboratory test that provides detailed information about the cells in the blood: red blood cells or erythrocytes, white blood cells or leukocytes and platelets.

The word blood count is a commonly used "abbreviation of the term complete blood count composed of the Greek words haima (blood), khroma (color), kytos (cell) and metron (measure) referring to the color and quantity of blood cells.

In reality this examination consists of a series, or panel, of tests through which it is possible to determine not only the number of the various types of cells, but also their characteristics and the substances that compose them.

A complete blood count includes:

  • calculation of the total number of white blood cells (WBC), immune system cells that increase with infection and inflammation. Since white blood cells can be of different types, depending on the specific function they perform, in the complete blood count they are collected in the so-called leukocyte formula which includes an assessment of the various types of WBCs present: neutrophils, lymphocytes, monocytes, eosinophils and basophils
  • calculation the number of red blood cells (GR), the most numerous cells in the blood, and throughout the body, which contain hemoglobin
  • definition of the levels ofhemoglobin (Hb), ferrous protein contained in RBCs that binds to oxygen molecules and transports them to different organs and tissues of the body
  • definition of the levels ofhematocrit (HCT), percentage of RBCs present in the total blood volume
  • evaluation of some physical characteristics (indices) of red blood cells:
    • mean corpuscular volume (MCV), measure of the average size of GR
    • average amount of hemoglobin (MCH), calculation of the average amount of hemoglobin that carries oxygen in red blood cells
    • mean corpuscular hemoglobin concentration (MCHC), calculation of the average percentage of hemoglobin present in red blood cells
    • extent of red blood cell distribution (RDW), measure of the amplitude of the variations in size of the GR
  • calculation of the number of platelets, the smallest cells in human blood, which have the function of promoting coagulation and healing of wounds from which blood comes out (haemorrhages)
    • mean platelet volume (MPV), calculation of the average size of platelets. This is important because young platelets are larger than old ones. A higher MPV value, therefore, indicates their higher production
    • amplitude of the distribution of platelets (PDW), measure of the variation of their size

The blood count is a very common test and is prescribed by the attending physician as part of the periodic control tests (routine tests) because it allows you to have a fairly complete picture of a person's general health. It may be necessary to perform it if there are disturbances, such as lasting weakness or fatigue, which the doctor believes may be caused by anemia; or if you have signs of uncommon inflammation, infection, bruising, or bleeding.

The blood count, therefore, is prescribed to ascertain (diagnose) and follow over time (monitor) various conditions and diseases affecting blood cells (for example, anemia, infections, inflammation, coagulation disorders or tumors).

It is also required to monitor the effects of chemotherapy, which can damage the production of cells by the bone marrow, or to control the effect of some drugs.

The test

The test

To perform the blood count, a small amount (a sample) of blood is required, usually a few milliliters.

In adults, blood is usually drawn from a vein in the arm or by a finger prick; in young children, it is usually obtained from the heel.

No special preparation is required. To perform the blood count alone, it is not necessary to be fasting.

The blood count, in general, is performed using automated tools. The collected blood is stored at room temperature in a test tube containing an anticoagulant, then it is transported to the analysis laboratory and analyzed with an electronic machine called counter. This instrument allows to analyze, in a few tens of seconds, the blood samples by reading the values ​​obtained twice and providing the arithmetic mean of the two measurements as the final value.

If the reading is not possible, or the two values ​​are too discordant, the machine does not produce results and signals this by writing a dash "-".



Normal blood count values ​​differ based on gender, age and the equipment used. They are different for children and adults and the laboratories provide different reference values ​​for the various age groups.

The values ​​outside the norm help to ascertain (diagnose) different diseases, some of them will have to be treated while others will be able to heal on their own.

For example, an increase in white blood cells can be a sign of infection or inflammation and suggests further tests to identify the cause. A decrease in white blood cells, on the other hand, can be caused by some drugs, by certain viral infections, by insufficient functioning of the bone marrow, by enlargement of the spleen, by liver disease or by excess alcohol.

A decrease in red blood cells is found in the case of anemia. An increase in red blood cells, for example, if you lose fluids due to diarrhea, dehydration or burns. Alterations in the physical characteristics (indices) of red blood cells can be due to various causes. For example, an increase in mean corpuscular volume (MCV) can be caused by a vitamin B12 deficiency, liver disease, thyroid disease or can occur during pregnancy. The mean amount of hemoglobin (MCH) can be low in cases of iron deficiency or inflammatory conditions.

The number of platelets increases when there is a loss of blood or in cases of inflammation and infection; it decreases when there are changes in the immune system, vitamin deficiencies, during chemotherapy, in the case of alcoholism or liver disease. Regarding the hemoglobin content of the RBCs, it must be remembered that its concentration varies according to the age of the person. At birth, for example, the values ​​are higher than in any other phase of life and decrease sharply in the immediately following period. .

The results of the examination must always be evaluated by the attending physician since any value, even anomalous, must be interpreted based on the general health of each person. Therefore, the relationship and dialogue with the treating doctor is essential to ask for information and clarifications, to express doubts and concerns.

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