The small blood count

The small blood count is often used for blood tests. EDTA blood is usually used for this. EDTA (ethylenediaminetetraacetic acid) is a so-called complexing agent.

This means that EDTA can bind calcium ions and forms complexes with them. These Ca2+ ions are now missing in the blood clotting process, so blood clotting cannot take place and the blood remains liquid. In the small blood count, the cellular components are examined.

Normally a man’s blood contains about 43-50% cellular components, a woman’s blood only about 37-45%. This cellular component of the total blood volume is called hematocrit. Especially during pregnancy, the hematocrit can decrease significantly.

The haematocrit is primarily dependent on the red blood cells, the erythrocytes, as these are the most common in terms of quantity. Per ul of blood, 4.3-5. 2 million erythrocytes are found in women; 4.8-5.2 million in men.

Erythrocytes serve to transport oxygen in the body and ensure that the oxygen absorbed is carried from the lungs to the whole body and to all organs. If there is a lack of oxygen, permanent stress or loss of fluid (for example, due to insufficient drinking), the number of erythrocytes in the blood is increased. Blood loss or iron deficiency leads to a reduced number of erythrocytes in the blood.

Besides the erythrocytes, the number of reticulocytes can also be determined. Reticulocytes are the precursors of the erythrocytes. Normally, only a few are found during blood tests, but if there is an increased formation of new blood (e.g. after severe blood loss), they may be found in greater numbers in the blood.

Next, the white blood cells, the leukocytes, are examined. In total, 4-10 thousand leukocytes are found per ul of blood. Among the leukocytes, a distinction is made between lymphocytes, monocytes and 3 types of granulocytes.

These are determined more precisely in the differential blood count and do not belong to the examination of the small blood count. Since leukocytes play an important role in allergic reactions, for example, they are found in increased numbers in the blood after an allergic attack, but also after inflammation or after an attack of gout. Their number increases enormously, especially in white blood cancer (leukaemia).

After a viral infection, for example the flu, the values can be lowered. Blood platelets (thrombocytes), of which 150-400 thousand are found per ul of blood, are also taken into account in blood tests. These are used for blood coagulation.

If our blood contains too few thrombocytes, this is called thrombocytopenia. Blood clotting cannot take place properly and this leads to an increased bleeding tendency. But it can also lead to thrombocytopathy.

Here the bleeding time is also prolonged despite a normal number of thrombocytes. However, since these are not fully functional, the bleeding time is longer and small punctiform bleedings (so-called petechiae) occur. In order to test whether the platelet number or shape is normal, the average platelet volume is used for blood testing.

Other parameters that are taken into account when examining the small blood count are the red blood pigment (haemoglobin), which binds oxygen. An Hb value of 12-16 g/dl is normal for women, for men the Hb value should be in the range of 14-18 g/l. The MCH (mean corpuscular hemoglobin), the MCV (mean corpuscular volume) and the MCHC (mean corpuscular hamoglobin concentration) can only be determined by calculations and give information about the properties of the red blood cells (erythorcytes).

The information serves as a differential diagnosis in the case of anaemia. A blood test can also provide a differential blood count. Together with the small blood count, both are called the large blood count.

The differential blood count is also based on EDTA blood or blood that has been collected using a small capillary. This capillary blood can, for example, come from the fingertip and, unlike whole blood, is not purely venous blood but contains certain substances (such as glucose) in increased concentration. The blood is now examined for the specific forms of white blood cells (leukocytes).

Leukocytes are divided into lymphocytes, which serve the specific immune defence; monocytes, which serve the general immune defence and granulocytes. Granulocytes are divided into neutrophilic, eosinophilic and basophilic granulocytes. The neutrophilic granulocytes serve the unspecific defence, for example against bacteria.

One can still differentiate between rod and segment nucleated neutrophil granulocytes, which do not differ in their function. In total, 3000-6000 neutrophil granulocytes per ul of blood should be found in this blood test. The eosinophilic granulocytes are responsible for the allergic reaction and can act against parasite infestation (e.g. a worm infection).

About 50-250 eosinophilic granulocytes should be found per ul of blood. The basophil granulocytes are also responsible for the allergic reaction. Only about 15-50 basophilic granulocytes are found per ul of blood.

A differential blood count is not one of the typical blood tests and is only carried out if there is a suspicion of a serious infection, a disease with parasites (parasitemia; for example in malaria) or a blood disease such as leukemia (blood cancer). After parasite infestation it can be determined that the number of eosinophilic granulocytes is greatly increased. If, on the other hand, the number of monocytes is elevated, this may indicate tuberculosis.

After an infection with the HI virus (HIV), the number of lymphocytes is reduced (lymphocytopenia). In blood tests of the small blood count and the differential blood count, the values of the individual cells are given in a reference range. The values of a healthy patient should lie within this range. Nevertheless, it is said that, according to the definition, every 20th value should lie outside the normal values. So if there are slight deviations, this does not necessarily indicate a disease.