What exactly is blood?


Blood is not simply a red liquid but a suspension of countless components. About 45% are cells, and 55% are plasma with soluble substances.

The plasma contains clotting factors, hormones, antibodies, electrolytes, and many other substances that serve communication between the different cells, organs and organ systems - messenger substances. The list is practically endless, and our understanding of the interaction of these substances is patchy at best...


On the other hand, we know quite a lot about blood cells. 

We differentiate here:


Erythrocytes - red blood cells that bring oxygen to all organs and give the blood its colour. By the way, erythrocytes comprise 85% of all body cells, with a weight of only 2.5kg.


Leucocytes are the cells of the immune defence. They are all grouped together under the name "white blood cells" but can be divided into various subgroups:

  • T-cells, T-helper cells, T-regulatory cells, T8- and T4-cells
  • B-cells, plasma cells
  • Granulocytes (neutrophils, basophils, eosinophils), lymphocytes, monocytes, macrophages

Platelets, without them, there would be no clotting. 

To enlarge and to view the description, simply click on a picture.


When donating blood, 450 ml of whole blood is taken and mixed with ACDC (citrate) to prevent clotting.


In the blood bank, the blood is then separated into three components: erythrocytes, plasma and buffy coat (containing the platelets). In addition to the 450 ml of blood, about 40-50 ml are collected in a small bag at the beginning of the donation. On the one hand, for the tests to be carried out and, on the other hand, for a practical reason. If germs enter the vein while the needle passes through the skin, they are diverted to the test bag so that only sterile blood ends up in the collection bag. 


The blood donation is centrifuged - at the top remains the plasma, which is squeezed off - in between is the so-called buffy coat with the white blood cells, and the platelets - this layer is further processed to separate the platelets from the leucocytes. And then, the red blood cells, the erythrocytes, are at the very bottom. These initially remain in the bag, are then resuspended with a medium, and the remaining leucocytes are removed in a filtration step. Finally, an erythrocyte concentrate remains, which has a volume of approx. 300ml, approx. 60% are packed red blood cells, and there is only little residual plasma in the nutrient fluid.


The plasma obtained from a donation is deep-frozen within 6 to 18 hours.


A platelet concentrate is produced from the buffy coat, which would be too small for transfusion. Therefore, between 4 and 8 such primary concentrates are pooled together, then filtered to remove the leucocytes and pathogen-inactivated (e.g., Intercept). Finally, the thrombocytes are resuspended in an additive solution in which they can be stored for up to 7 days at 20-24°C with constant rocking.

Blood cells come from the bone marrow from a stem cell that does not yet "know" what it will become. It only knows - it will become a blood cell.

This is what the blood smear of a healthy person looks like. The many pink cells with a pale spot in the middle are the red cells (erythrocytes). The many small purple dots, these are the thrombocytes. And the slightly larger cells with a nucleus (sometimes lobulated, sometimes just round) are the white cells (leucocytes).

Last update on 12.08.2023