Since 2001, staff at blood banks have had to filter all the stored blood in order to remove the white blood corpuscles from it. This is because white blood corpuscles can have negative consequences for recipients of blood transfusions: sometimes they cause an immune reaction whereby the patient generates antibodies against the antigens which are located on the surface of the foreign cells. This results in shivering fits and fever. As a result of this, some patients are only able to receive blood from a very small number of donors. Furthermore, the white blood corpuscles often carry pathogens, certain viruses for example, which could infect the patient. It is also possible that the new variant of the Creutzfeldt-Jakob disease is transmitted in this way.

Filtering reduces the number of white blood corpuscles in the donated blood to a minimum. Blood banks use sterile closed blood-bag systems for this with all the necessary bags, filters and tubing already integrated. Gravity ensures that the blood flows through the filter from the upper bag to the lower bag. The filter is made of a fleece of compressed fibres which have various different pore sizes. As a result of their size and interaction, the white blood corpuscles stick to the fibre material and in this way are removed from the blood.

The researchers at the Fraunhofer Institute for Production Technology and Automation IPA in Stuttgart have a new system which monitors this kind of blood filtering and can indicate if a filter is defective or that a filtering process has failed. Here, an important criterion is how long the filtering takes: for every filter there is an optimal length of time for the filtering process. Each manufacturer of blood products has to define the length of time that will guarantee the quality of the stored blood. If the blood flows more quickly, this could be an indication that the filtering is not functioning properly. The stored blood can only then be used after an extensive quality control has been performed. If the blood flows more slowly, this could indicate that the quality has been impaired and, as a precaution, that the stored blood should not be used. Up to now blood bank staff have had to monitor how long the filtering takes using a standard stopwatch: they start the filtering process, return at the time specified and dispose of all the blood samples which have not yet finished filtering. However, using this method, the staff cannot recognise if there is a hole in the filter and whether the blood has flowed through more quickly.

This new monitoring device has a flow gauge behind the filter which registers when the blood finished filtering. The system stores in a database the length of time a specimen needed to drip through. It is possible to see on the screen afterwards in which bags the filter worked correctly and in which it did not. The device can accommodate 24 bags simultaneously. “Our system makes filtering blood safe and uncomplicated”, says Oliver Refle from IPA. Researchers at IPA developed it together with their colleagues at the blood centre in Stuttgart. It will be on the market in the next few weeks. The researchers will be presenting their new system at the medical technology exhibition MedTec in Stuttgart from 3rd to 5th March.