The majority of blood cells are red blood cells. After separation, the hematocrit (the percentage of red blood cells in the total blood) is typically reported as 45%, even though the other cells form a very thin white layer between the red blood cells and the plasma. 

An erythrocyte is a biconcave disc about 7µm in diameter. Due to the haemoglobin, erythrocytes (and therefore blood) are red. Haemoglobin is the blood molecule that transports oxygen to the organs and removes carbon dioxide. It consists of four subunits - two alpha and two beta chains, haem, globin and iron-containing protoporphyrin. One haemoglobin molecule can bind four oxygen molecules. There are, on average, 200,000 haemoglobin molecules in an erythrocyte. It has the critical ability to take up oxygen first but then release it into the tissue. How much oxygen is released depends on the oxygen saturation of the respective tissue. However, temperature, pH, 2,3-biphosphoglycerate concentration, and CO2 concentration also influence the ability of haemoglobin to release oxygen in the tissues.

A small example: during physical work, the muscle consumes much more oxygen than at rest. Muscle contraction, from a chemical and biological point of view, generates heat and lactic acid. This raises the temperature and the pH drops. And the consumption of oxygen produces CO2, so the CO2 saturation increases. All this leads to oxygen being released more easily. It's a self-regulating system. How this is regulated and influenced is far beyond the scope of this website (and probably the interest of most readers...). But I always find numbers particularly interesting, so here's one fun-fact: 1 litre of blood transports about 200ml of oxygen :-).

Red blood cells do not have a nucleus and are removed from the bloodstream after 120 days. They break down into their components, especially the iron from haemoglobin, in the spleen and liver, which is then recycled. 

Except for stem cells and granulocyte concentrates, all other blood products intended for transfusion can be prepared in two ways:

• One way to produce blood products is by separating a whole blood donation into its components. This production method requires dedicated and courageous blood donors who spend about 45-60 minutes giving 500 ml of blood at blood drives, with the actual donation process taking only about 10 minutes.
• The apheresis method, on the other hand, offers a more efficient approach. In this process, a brave donor is connected directly to a machine where the blood is collected and centrifuged. Different centrifugation speeds create layers that always contain a specific type of cell. This allows for selective filtering, with the rest of the blood returned to the donor. While this process may take longer, up to 1.5 hours, it is less stressful for circulation. It's important to note that stem cells and granulocytes can only be collected in this way, making it a crucial and efficient method in the production of blood products. There are approx. 250 ml of blood suspension in an erythrocyte concentrate.

The required haematocrit is 50-70%.

The liquid (SAG-M) in which the cells are stored is a nutrient solution that keeps red blood cells suitable for transfusion for up to 42 days. Since around the year 2000, all cellular blood products have been filtered to remove leukocytes. The maximum remaining leukocyte content in a blood unit must not exceed 10^6. The storage temperature of blood products should be between 2 and 6°C. However, a drop in temperature is more problematic because it can cause the cells to break down. If the temperature rises, red blood cells may be stored at room temperature for another 6 hours, but then they must be transfused. A blood product that has been opened (red blood cells, platelets, plasma) MUST be transfused within 4 hours.

And in case anyone wonders what all those short tubes are for - they are also filled with the blood from the blood unit and sealed off into segments approx. 2 -3 cm long. A compatibility test must be done every time a red blood unit is ordered for a patient. For this, the blood from the bag is needed. However, since the bag must not be opened, exactly these segments are taken for this purpose.

Last update on 01.07.2024.