Blood count


The blood count is a simple and usually inexpensive examination method used by the physician. By means of a blood sample taken from the patient’s venous blood, certain markers and parameters in the blood serum can be measured and determined in the laboratory. The evaluation of the blood sample is now carried out largely automatically by a specialized device in the laboratory, so-called hematology devices.

Only in certain cases are blood smears examined under the microscope by the laboratory staff themselves. In addition to the evaluation of blood cells, solid blood components and blood pigment, numerous organ-specific parameters (e.g. liver values, kidney values, electrolytes, thyroid values etc.) can also be determined from the blood serum.

However, these organ values are not determined in the blood count in the actual sense, but from the blood that is collected in a separate tube. A distinction is generally made between taking a small and a large blood count. The small blood count is the basic diagnostic tool in blood testing, in which only the number of red and white blood cells (erythrocytes, leukocytes), platelets (thrombocytes), blood pigment content (haemoglobin) and the ratio of solid to liquid blood components (haematocrit) are determined.

The large blood count, on the other hand, is an extension: the small blood count is combined with the so-called differential blood count, in which the subclasses of white blood cells are determined individually and separately in their existing numbers. In addition, numerous other parameters can be determined, which, however, do not fit into the categories “small” or “large” blood count, but are either determined as a supplement or, depending on the question, are organ-specifically groundbreaking (liver, kidney values, etc.) Both the large and small blood count are determined from so-called EDTA blood: The blood of the patient to be examined is taken by means of an EDTA tube containing a substance that inhibits the clotting of the blood and thus allows the laboratory to examine the blood outside the body.

The small blood count

The small blood count represents the basic form of the blood count. The parameters determined by the laboratory in a small blood count include the number of red blood cells (erythrocyte count), the number of white blood cells (leukocyte count), the number of platelets (thrombocyte count), the concentration of red blood pigment in the blood (haemoglobin concentration), the amount of solid blood components or the ratio of solid to liquid blood components (haematocrit) and the so-called erythrocyte indices MCH (mean corpuscular haemoglobin quantity of a single erythrocyte), MCV (mean corpuscular volume of a single erythrocyte) and MCHC (mean corpuscular haemoglobin concentration of all erythrocytes). A large blood count is the combination of a small blood count (Hb, number of erythrocytes, leukocytes and platelets, MCH, MCHC, MVC) and a differential blood count (breakdown of individual white blood cells).

In the large blood count, the subgroups of white blood cells are examined more closely. Changes in their division allow for indications of various diseases, as each subgroup has its own special task. In percent, the division would look as follows: The granulocytes represent the main part of the white blood cells, followed by the lymphocytes and monocytes.

Reasons for a large blood count are suspected diagnoses, such as diseases of the blood system, severe systemic diseases, infections, parasite infestation (e.g. malaria etc.) or congenital disorders of the red blood cells (e.g. sickle cell anaemia). – 60% Neutrophil granulocytes (= rod and segmental nucleus granulocytes)

  • 30% lymphocytes
  • 6% monocytes
  • 3% eosinophil granulocytes
  • 1% Basophilic granulocytes

Erythrocytes are red blood cells whose main task is to transport oxygen in the blood.

For this purpose, oxygen is bound to the protein haemoglobin, which is present inside the erythrocytes. The standard values for erythrocytes in a healthy adult man are between 4.3 and 5.9 million/μL blood; in a healthy adult woman between 3.5 and 5.0 million/μL. The formation of erythrocytes occurs in the bone marrow and ends in the liver and spleen.

The normal survival time of red blood cells is approximately 120 days. Pathological changes in erythrocytes can affect their number, shape, size and function and can be detected by means of a blood count. If the number of erythrocytes is reduced, anaemia is usually present.

Causes of anaemia can be acute or chronic bleeding, kidney disease (renal anaemia) or iron or vitamin B-12 and folic acid deficiency. Leukaemia or other types of cancer can also be associated with reduced red blood cell levels. If erythrocytes die prematurely, this is called haemolytic anaemia.

The causes can be congenital erythrocyte defects, infections or heavy metal poisoning. Elevated erythrocyte values, on the other hand, are usually caused by a lack of oxygen, which can be caused, for example, by diseases of the lungs or heart or by a stay at high altitude. Diseases of the bone marrow, such as polycythaemia vera, can also be associated with elevated erythrocyte values.

Erythrocytes that are too small are called microcytes. These usually occur in the event of iron deficiency. Too large erythrocytes (also called macrocytes) are usually the result of alcohol consumption or a lack of vitamin B-12 and folic acid.

Red blood cells of altered shape can occur in cases of anaemia, genetic defects (sickle cell anaemia) or heart valve replacement. The consequence is usually an increased breakdown of erythrocytes with subsequent anaemia. Haemoglobin is also called the red dye of the erythrocytes and has the task of binding oxygen in the innermost part of the red blood cells.

The normal values for haemoglobin are between 13 and 18 for an adult man and between 11 and 16 for women. A reduced haemoglobin value is present in anaemia, kidney disease or inflammatory bowel disease such as Crohn’s disease. An elevated haemoglobin value is found with increased erythrocyte numbers, e.g. during stays at high altitudes.

The MCV value is a blood value that is determined by the doctor when a small blood count is taken and can be determined by the laboratory. MCV is the abbreviation for the so-called “mean corpuscular volume” of the red blood cells (erythrocytes), meaning the mean volume of a single red blood cell. In the laboratory, this value is usually calculated on the basis of the light refraction of the erythrocytes by a specific device (flow cytometry) or on the basis of a simple calculation formula in which the value of the cellular blood proportion (haematocrit) is divided by the total number of erythrocytes in the blood.

The normal range for the MCV value is approximately between 83 and 97 fl (femtolitres). In (blood) diagnostics, it is regarded as one of the important markers for various (blood) diseases, especially for anaemia. As a rule, the MCV value is determined together with the MCH and MCHC values and then allows an important subdivision of an existing anaemia.

If the MCV value is reduced, this is often a sign that the red blood cells are too small (microcytic), if it is too high, the erythrocytes are therefore too large in volume (macrocytic). Like the MCV value, the MCH value is a blood value that can be determined by the laboratory in the course of taking a small blood count. MCH stands for the “mean corpuscular haemoglobin content”, as the red dye content that each individual red blood cell (erythrocyte) has.

In the laboratory, this value is usually calculated automatically by a specific device (flow cytometry), which can measure the dye content in the erythrocytes on the basis of the refraction of light in the red blood cells. However, the MCH value can also be calculated by dividing the total haemoglobin value, which can also be determined in the blood count, by the total number of erythrocytes. The standard for the MCH value is between 28 and 33 pg (picogram).

Like the MCV and MCHC values, the MCH value is a diagnostic marker for diseases of the blood system, especially anaemia. If the MCH value is lowered, this is an indication that the red blood cells contain too little red dye (hypochrome), if it is raised, they contain too much of it (hyperchrome). In addition to the MCV and MCH values, the MCHC value is another important diagnostic marker for diseases of the blood system – especially for anaemia – which can be determined by the laboratory by taking a small blood count.

The abbreviation MCHC stands for the “mean corpuscular haemoglobin concentration”, i.e. the concentration of the total red pigment (haemoglobin) of all erythrocytes in the blood of the respective patient. This value can be calculated by dividing the total red dye concentration, which can also be determined by the laboratory, by the value of the solid blood components (haematocrit) in the blood. Another way to determine the MCHC value is to calculate it from the MCH and MCV values that may already be known (MCHC = MCH/MCV).

The standard for the MCHC value is between 30 and 36 g/dl (grams per deciliter). Unlike the MCV and MCH values, the MCHC value often hardly changes at all, since the MCH and MCV values usually move in the same direction, i.e. they rise or fall together and the quotient therefore remains the same. For this reason, the MCHC value generally only serves as a plausibility check for the evaluating physician.

Leukocytes or “white blood cells” are certain cells in the blood whose main task is to defend against pathogens. The formation and maturation of leukocytes occurs in the bone marrow from a common precursor cell (stem cell). Misprogrammed or defective leukocytes are usually removed while still in the bone marrow; functional, mature leukocytes are then released into the blood.

In some cases, however, the survival of “wrongly programmed leukocytes” can occur. These can then attack and destroy the body’s own cells and tissue. The consequences are autoimmune diseases such as the well-known lupus erythematosus or multiple sclerosis.

The determination of leukocytes is part of routine blood tests. They are carried out when there is a suspicion of inflammation or infection, when leukaemia is suspected, in cases of infarction and poisoning, as well as during radiation or immunosuppressive therapies. The standard values for adults should be between 4-10.

000 leukocytes/μL. Typical diseases associated with low leukocytes include viral diseases, bacterial diseases such as typhoid fever, bone marrow diseases in which the formation of new leukocytes is prevented or hypersplenomegaly in which leukocytes are broken down more quickly. The white blood cells are elevated in inflammations (e.g. in pneumonia), in many bacterial infections, in leukaemias (blood cancer) or in very heavy nicotine consumption, this is also called “isolated leukocytosis”.

An increase in lymphocytes is mainly present in viral infections (mumps, measles), autoimmune diseases or leukaemias. A decrease can occur in the context of various types of cancer or drug side effects. Monocytes are elevated in tuberculosis in particular.

With granulocytes, different subclasses of granulocytes are elevated, depending on the cause of the disease. Neutrophil granulocytes are elevated mainly in bacterial infections. In severe infections such as sepsis, the so-called left shift often occurs.

Here, due to the high demand for cellular defence, precursors, i.e. immature granulocytes, are also released. This effect is shown in the blood count as a left shift. Eosinophilic granulocytes are elevated, especially in the case of parasite infestation by worms or in allergic reactions.

Basophilic granulocytes are elevated in blood cancers such as chronic myeloid leukemia. If leukocytes, erythrocytes and thrombocytes are reduced, this is called pancytopenia (reduction of all cell rows). This is usually an indication of severe bone marrow damage.

If two or more cell rows are altered (e.g. increase in leukocytes and decrease in erythrocytes), this is usually an indication of leukemia. Thrombocytes are small, disc-shaped blood platelets that are responsible for blood clotting in the body. This plays an important role, especially in the case of cuts.

If there are too few or too many functionless thrombocytes in the body, bleeding can only be insufficiently stopped. The consequence is that injuries bleed longer. The normal survival time of thrombocytes is 5-9 days.

They are then broken down in the liver and spleen. Platelets are usually routinely included in a blood count or specifically determined when patients suddenly bleed more than usual, when thromboses occur or when heparin therapy is to be monitored. The standard values for thrombocytes in adults are 150,000 to 400,000 per microliter.

Causes of thrombocytopenia (too few thrombocytes) can include leukaemia and myelodysplastic syndrome, autoimmune diseases such as TTP or immune thrombocytopenia, chronic liver damage or haemolytic-uremic syndrome (HUS). Cases in which the number of platelets is increased are acute infections, tumor diseases or myeloproliferative diseases such as essential thrombocythemia. Behind the abbreviation CRP is the term “C-reactive protein”, which stands for a protein in human plasma that is produced in the liver and then released into the blood.

It belongs to the so-called “acute phase proteins” and is therefore in the broader sense a protein of the immune system, which in an “acute phase” sets the defence mechanisms in motion and subsequently attaches itself to bacteria, so that the complement system (part of the immune system) and certain defence cells (e.g. macrophages) are then activated. Under physiological or healthy conditions, CRP is present in the blood in very small quantities only, the norm being an upper limit of 1mg/dl. The CRP value is always elevated when inflammatory processes occur in the body (e.g. infectious and non-infectious inflammations such as respiratory tract or urinary tract infections, appendicitis or gall bladder inflammation etc.

), although it cannot be traced back to a specific disease, so that further examinations must follow for a more precise diagnosis. In general, the CRP value increases more strongly with bacterial infections than with viral ones. – Rod-nucleated granulocytes : 150-400/μL

  • Segmented nuclear granulocytes: 3.

000-5. 800/μL

  • Eosinophil granulocytes : 50-250/μL
  • Basophilic granulocytes : 15-50/μL
  • Lymphocytes : 1. 500- 3.


  • Rod-nucleated granulocytes : 150-400/μL
  • Segmented nuclear granulocytes: 3. 000-5. 800/μL
  • Eosinophil granulocytes : 15-50/μL
  • Basophilic granulocytes : 1500-3000/μL
  • Lymphocytes : 285-500/μL