Blood count

In the small blood count the number of thrombocytes is always determined because they have an important function in the coagulation cascade. The thrombocytes can be recognized here as small blood platelets without a cell nucleus. Compared to the white blood cells (leukocytes) and the red blood cells (erythrocytes) they look tiny and therefore stand out.

In addition, they are most frequently represented in the blood count, so that many small round “dots” appear between individual larger erythrocytes and leukocytes. In general, thrombocytes are quite round but not always circular, about 1-4 μm large and very flat. They survive in the blood for about 5-12 days, then they are broken down in the spleen, liver or lungs.

Since a blood sample has an enormous number of platelets, they must be counted with a fully automated measuring device because a human would take too long. To prevent the platelets in the blood sample from clumping together, an additional substance is always added, which prevents the platelets from clumping together and then lying as one big lump at the bottom of the blood sample, because in this way the individual platelets could no longer be counted.Therefore ethylenediaminetetraacetate, EDTA for short, is added to the blood sample. The blood together with the anti-coagulant is called EDTA blood.

Normally the thrombocytes in this EDTA blood do not clump together. Rarely, however, it happens that despite the EDTA, some platelets clump together and settle at the bottom of the blood sample. The automatic counting machine cannot detect these clumped platelets because they are too large for a normal platelet.

As a result, the meter indicates that the patient has too few platelets, although this is not the case. The physician speaks of a pseudothrombocytopenia. To prevent this false diagnosis, citrate can be added to the blood instead of EDTA.

In these citrate tubes the thrombocytes do not clump and can then be evaluated correctly. The thrombocyte count in the blood has a normal range of 150. 000-400.

000 units/μl (one μl corresponds to 0.001 l). A value below that (>150. 000/μl) is called a deficiency and in technical terminology thrombocytopenia (see below).

Values above (450. 000 – 1000. 000/μl) are called excess and thrombocytosis (see below).

This is usually temporary and can occur in response to trauma, surgery, blood loss or chronic inflammation. If the number of thrombocytes per μl exceeds one million, this is called thrombocythemia, which can occur in certain bone marrow diseases. = A patient has too many thrombocytes if the number of thrombocytes in the blood rises to over 360 thousand / μl blood.

This can have various causes. For example, an increased number of thrombocytes (thrombocytosis) occurs after removal of the spleen, since the spleen is a breakdown organ of the thrombocytes. If the spleen can no longer break down the platelets, more platelets are automatically produced.

If there is a larger loss of blood, for example during an operation or an accident, the body produces more platelets to close the wounds. As a result, the number of thrombocytes in the blood often increases after major surgery. As this represents a risk of thrombus formation, so-called anticoagulants are often given after major operations or injuries, i.e. medications that prevent the accumulation of thrombocytes and thus make the blood more fluid.

A blockage of the blood vessels by thrombocytes thus becomes very unlikely, but the risk of bleeding increases. The number of thrombocytes can also increase in inflammatory processes, as well as in diseases of the bone marrow. The thrombocytes originate from the so-called megakaryocytes, which in turn originate from stem cells via several intermediate stages in the spinal cord.

If overstimulation occurs during this maturation process, more thrombocytes are produced. = A patient has too few thrombocytes as soon as the number of thrombocytes in the blood drops below 140,000 per μl blood. This can have various causes.

For example, after a severe infection it is normal that the number of platelets drops because many platelets have been “used up” by the infection. In addition, a vitamin B12 or folic acid deficiency can lead to so-called megaloblastic anemia, in which the number of all cellular components of the blood is reduced. The number of thrombocytes also falls into very low physiological ranges or is pathologically reduced, in which case it is thrombocytopenia.

These two causes are probably the most common causes of thrombocytopenia, but there are also much more serious but rare causes. One of these is a pathologically low platelet count due to blood cancer (leukemia). In this case, the normal bone marrow is displaced and thus the number of mature blood cells normally present in the blood is reduced and are partially replaced by immature cells.

Thus, not only thrombocytes are found in the blood but also megakaryocytes in some cases. However, not only blood cancer can be responsible for thrombocytopenia, but also the intake of certain drugs such as chemotherapeutic agents after or during cancer treatment. It is particularly important to monitor the blood count regularly.

In addition, there are various autoimmune diseases in which autoantibodies are formed against the thrombocytes.These autoantibodies ensure that the platelets are broken down and are produced by the body itself (therefore “auto”). Idiopathic thrombocytopenic purpura (ITP) and lupus erythematosus disseminatus should be mentioned. In very rare cases, an increased supply of lead (lead intoxication) can also reduce the number of thrombocytes.

Especially in older patients, a premature reduction of thrombocytes can occur more frequently. This can be the case, for example, with an artificial heart valve or due to dialysis with extracorporeal circulation. A reduced number of thrombocytes is characterized above all by a higher tendency to bleed. Patients bleed faster and sometimes have difficulty stopping the bleeding. In most cases, thrombocytopenia can be recognized by the fact that patients have punctiform bleeding in the legs and the rest of the body (petechiae).