What is a blood count?

Blood is a suspension of red blood(rb) cells (erythrocytes), white blood cells (leukocytes), and platelets in plasma. Blood morphology is a popular, very often performed test consisting in their quantitative and qualitative analysis.

How is a blood count taken and how to prepare for it?

5 ml of blood are collected from the vein in special test tubes containing EDTA (a substance preventing the collected blood from clotting).

How to prepare for a blood count test?

Before the examination, the patient should not exercise or stay in a standing position for a long time. He should also be fasting for 8 hours before the test.

It should be remembered that any abnormalities in the blood counts must be verified by repeating the test – laboratory errors are not uncommon.

Blood morphology – indications

The morphology is often performed prophylactically, without suspecting the disease. The test is used mainly in the diagnosis of anemia (anemia) and infections. It also allows an overall assessment of the body’s water management (e.g. detecting dehydration).

Morphology – contraindications

In order to perform the morphology, blood is collected in a small amount, which does not affect the patient’s condition. For this reason, there are no contraindications to its implementation.

Red blood cells (erythrocytes) – RBC

Normal: women 3.5–5.2×106 / µl, men 4.2–5.4×106 / µl.
This test tells us about the red blood cell content in 1 µl of blood. Erythrocytes are blood cells with a disc-shaped, biconcave shape, playing a very important role – the transport of oxygen necessary for life from the lungs to all tissues of our body, as well as the transport of carbon dioxide from the tissues to the lungs for its discharge into the atmospheric air. Their production, which takes place in the bone marrow, requires a number of micro- and macroelements – the most important are iron, vitamin B₁₂andfolic acid. The lifetime of a single erythrocyte is 120 days – after it expires, the erythrocyte is destroyed in the reticuloendothelial system, located in the spleen and liver.

The causes of the increased number of red blood cells

• The most common cause of an increased number of red blood cells is dehydration (this causes the blood to thicken, making red blood cells a greater percentage of its volume).
• States of chronic hypoxia of the body.
  Erythrocytes are oxygen carriers in our body, so their production increases in response to hypoxia. When this happens, the kidneys begin to produce more erythropoietin (EPO), a hormone that stimulates the bone marrow to produce red blood cells. Hypoxia may occur in the case of:
  • stay at high altitudes.In high mountain areas, air pressure is lowered, making gas exchange in the alveoli more difficult.
  • smoking a cigarette.Tobacco smoke contains carbon monoxide, which is carbon monoxide. Since it has a much greater ability to bind with hemoglobin than oxygen (7 times greater), when tobacco smoke is inhaled, carboxyhemoglobin is formed in place of oxygenated hemoglobin, which is unable to carry oxygen.
  • obstructive sleep apnea (OSA)– a common disease accompanied by hypoxia. It consists in numerous, long (even several minutes) pauses in breathing during sleep. During these breaks, the oxygen reserves in the erythrocytes are depleted – and therefore hypoxia.
  • congenital heart defects, in which deoxygenated (venous) blood mixes with oxygenated (arterial) blood – these include defects in the atrial or interventricular septum, the patent ductus arteriosus of Bottal, or rare syndromes – Fallot’s tetralogy or the relocation of the main vessels.
  • lung diseases – deoxygenated venous blood goes from the right ventricle of the heart to the lungs, where gas exchange takes place, consisting in the release of carbon dioxide (CO₂) from the erythrocyte and the intake of oxygen (O₂). After the blood is oxygenated, it goes to the left ventricle of the heart, and then to all our organs and tissues. In the presence of lung diseases such as chronic obstructive pulmonary disease (COPD) and the rare pulmonary fibrosis or cystic fibrosis, gas exchange is impaired.
• Polycythemia vera is a very rare disease that causes an increase in hematocrit – in its course there is an uncontrolled increase in the production ofredblood cells.
• Erythropoietin (EPO) secreting tumors– also an extremely rare cause of the increase in hematocrit.
• Effects of glucocorticoids in the course of steroid therapy orCushing’s syndrome.

The causes of the decreased number of red blood cells

• The production of erythrocytes is insufficient (then we are dealing with anemia). The following types of anemia can be distinguished:
  • Deficiency– This is the most common type of anemia. Most often it is caused by a deficiency of iron, vitamin B12 or folic acid – substances needed for their production. The most common cause of iron deficiency is chronic bleeding, others are malabsorption syndromes or increased demand (e.g. during puberty or pregnancy).
  • in the course of chronic diseases– chronic disease is the second most frequent cause of anemia, right after iron deficiency. In the course of various types of infections, cancer or autoimmune diseases, the immune system is stimulated, which results in a reduction in the production of red blood cells.
  • haemorrhagic– in the case of sudden or chronic blood loss, fluid permeates from the extracellular space to the blood vessels – thus the blood is thinned, and thus the hematocrit value is reduced.
  • haemolytic anemia is caused by abnormal, premature breakdown of red blood cells.
    • Haemolytic anemiais divided intocongenital– the reason for the breakdown of erythrocytes is then their abnormal structure (e.g. congenital spherocytosis, thalassemia) and acquired – erythrocytes are properly built, but there is a factor causing their disintegration (e.g. anti-erythrocyte antibodies, artificial heart valve, infections)
    • aplastic– occurs in the course of damage to the bone marrow, which is the site of erythrocyte production (exposure to ionizing radiation, toxic chemicals, some drugs).
  • The body is overloaded, but this is very rare.Hematocrit – HCTNormal: women 37–47%, men 40–54%
    Hematocrit tells about the volume of the whole blood as the volume of red blood cells (erythrocytes) themselves. In modern automatic analyzers, hematocrit is calculated on the basis of the number and volume of red blood cells; in traditional methods, hematocrit is measured directly by centrifuging a test tube with blood – the erythrocytes, having a greater density than the plasma in which they are suspended, migrate to the bottom of the test tube. After centrifuging, you can read the result using the measuring cup.The reasons for the increase and decrease in hematocrit are the same as for the number of red blood cellsHemoglobin – HbNormal: women 12–16 g / l, men 14–18 g / l dd
    Hemoglobin is a protein contained in the erythrocyte whose function is to transport oxygen molecules from the lungs to the peripheral tissues. It is the hemoglobin that gives the red color of the red blood cell. The above test shows the number of grams of hemoglobin in 1 liter of peripheral blood. It is the best test for the diagnosis of anemia. When making a decision about a blood transfusion, the doctor uses the result of this test.The cause of the increase and decrease in hemoglobin is the same as for the number of red blood cells.RBC indicators – red cellRed blood cell indicators tell of the structure of red blood cells. Often in healthy people there are slight deviations from the norm.Average hemoglobin content in the blood cell – MCHStandard: 27–31 pgMean concentration of hemoglobin in the blood cell – MCHCNormal: 32–36 g / dlThe MCH and MCHC indicators allow the assessment of the amount of hemoglobin contained in a single erythrocyte.The reasons for the increase in MCH and MCHCIncreasing these indicators is very rare, including in the case of hereditary spherocytosis. In this disease, the erythrocyte takes on a spherical shape instead of a disc-shaped one, and the increase in MCH and MCHC is caused by partial dehydration of erythrocytes, and thus concentration of hemoglobin in it.Reasons for reducing MCH and MCHCThe reduction of these indicators is a more frequent situation. Most often, the reduction in MCH and MCHC is due to:
  • iron deficiency which is necessary for the production of hemoglobin. In such a situation, it is produced in an insufficient amount, which translates into a reduction in its concentration in the erythrocyte.
  • Another, less common reason for the reduction of MCH and MCHC is thalassemia – a genetically determined disease in the course of which the synthesis of hemoglobin is reduced.Average blood cell volume – MCVNorm: 82-92 flReasons for reducing MCV
  • The reduction in MCV is most often associated with iron deficiency anemia, where the blood cell volume can then be 60–70 fl.
  • Hypertonic dehydration – this is a disturbance of the body’s water balance, which occurs in the event of loss of water only, with a slight loss of electrolytes (insufficient fluid intake, significantly increasedglucoselevels , diabetes insipidus). Then, their concentration in the blood increases and water escapes from the erythrocyte, which leads to a reduction in its volume.
  • Hypertonic hyperhydration – the causes of this water disorder may be renal failure or consumption of salt water. As with hypertonic dehydration, it causes water to escape from the red blood cell.
  • Thalassemia also results in a reduction of MCV, despite normal or even increased iron content in the body.
  • Anemia in the course of chronic diseases – rarely, only in severe casesReasons for increasing MCV
  • Most often it is caused by anemia due to vitamin B₁₂and folic acid deficiency (macrocytic anemia, MCV increase up to 150 fl). There are many reasons for this:
    • Vitamin B₁₂and folic acid deficiency in the diet – in the case of a vegan diet, in anorexics, alcoholics
    • Stomach diseases (cancer, inflammation) – intrinsic factor (IF), produced by stomach cells, is needed to absorb vitamin B12 from the gastrointestinal tract. It is rare for them to produce antibodies against this factor or against the cells in the stomach that produce this factor. We are then dealing with pernicious anemia (Addison’s and Biermer’s)
    • Diseases of the small intestine (cancer,Crohn’s disease) – the complex of vitamin B₁₂and internal factor is absorbed in the small intestine.
  • Hypothyroidism– The increase in MCV is slight, rarely exceeding 100 fl.
  • Hypotonic dehydration – it occurs when a dehydrated patient takes electrolyte-free fluids (e.g. tea) – then the water from the blood flows to the erythrocytes, resulting in an increase in their volume.
  • Hypotonic hyperhydration – most often caused by an excessive supply of electrolyte-free fluids in patients with impaired renal function.
  • Myelodysplastic syndromes – these are serious diseases of the bone marrow, but they are extremely rare.
  • Increased MCV may occur in pregnant women as well as in newborns, but this does not indicate the existence of the disease.
  • The percentage of reticulocytes is increased when the number of red blood cells is reduced to compensate for their deficiency, which is the body’s normal response. This phenomenon occurs in the caseof haemorrhagicand haemolytic anemia, staying at high altitudes and in the case of compensating for vitamin B₁₂or iron deficiency.
  • The percentage of reticulocytes is reduced when the bone marrow becomes ineffective (deficiency, aplastic anemia in the course of chronic diseases)
  • The increase in the total number of leukocytes is most often caused by an infection in the body. In the course of infection, young forms of leukocytes are released from the bone marrow into the blood in order to fight the pathogen more effectively – their number can reach 20,000 / µl.
  • A significant increase in the number of leukocytes (> 30,000 / µl) may be associated with neoplastic disease (leukemia, lymphoma), but it is a rare situation.
  • A slight, temporary increase may take place if we do not follow the recommendations regarding the preparation of blood counts – we eat a meal or exercise before the test.
  • the beginning of the infection – at the very beginning of the infection, the leukocytes circulating in the blood gather at the site of the infection. Before the bone marrow releases leukocytes to restore their proper amount in the blood, you may see leukopenia, then called pseudoleukopenia, on a blood test.
  • a history of an acute viral infection, such as acoldorflu
  • severe malnutrition (anorexia)
  • treatment with glucocorticoids and other immunosuppressants, some antipsychotics,
  • neoplastic diseases of the blood (leukemia)