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The Process of Donating Platelets

 
 
 
Platelets may be collected either from one person called single donor platelets or may be pooled from 5 different buffy coats to make one pooled platelet bag. 

 
Pooled Platelets
Another type of platelet component is referred to as ‘pooled platelets’. When donors visit a donation session to donate whole blood (WB), this is taken to our laboratories for processing. The bag is split up into red cells, a buffy coat (platelet rich plasma) and plasma, which will each become components in their own right for transfusion purposes. The buffy coat is where the platelets are found. Five such buffy coats (of the same ABO and RhD blood group) are ‘pooled’ together to form one unit of ‘pooled platelets’ (since the platelets are derived from multiple donors). So, in reality, we are all platelet donors!

 

Single Donor Platelets
Platelets can be collected directly from a donor by means of a specific machine. This machine draws whole blood in a special reservoir and separates the platelets from the rest of the blood by centrifugation. The platelets are collected and stored in a special bag which allows for gaseous exchange; while the rest of the blood (that is red cells and plasma) is returned to the donor. This constitutes one cycle. To make one unit of platelets the machine performs 6-8 cycles, each lasting about 10 minutes. This unit of platelets thus collected is called ‘single donor platelets’ since, as the name implies, platelets are derived from just one donor. 
  
What are pooled and single donor platelets (SDP) used for?
Platelets are an important part of the way our blood clots to prevent bleeding. Platelet components are thus transfused to treat or prevent haemorrhage. Apart from patients with massive blood loss, the biggest group of patients requiring (regular) platelet transfusions are those with haematological malignancies. Patients suffering from leukaemia and other cancers of the blood may experience a severe drop in the number of platelets in their circulation (platelet count). Should this count decrease to these very low levels, the patients may bleed from their gums and from under the skin. More severe haemorrhage may also occur and this could even be fatal; hence the importance of platelet transfusions in this patient group. 
   
Who can donate platelets?
Platelet donors are selected from among regular whole blood donors. The donor needs to satisfy specific criteria so as to be recruited as an ‘SDP’ donor. These include the following:
    

The donor should be a regular donor i.e. already donated whole blood twice: First time blood donors are not allowed to donate platelets, since donor veins have to be assessed for suitability for platelet donation (refer to following point). Also, if a donor cannot tolerate a whole blood donation, s/ he is not recruited as a platelet donor, as platelet donation takes more time and the donor is more likely to suffer from an adverse reaction.

    

The donor must have 'suitable' veins: Since the machine draws and returns a considerable amount of blood back to the donor, it is necessary that the vein must be of a certain calibre (roughly the size of a little finger!). This is preferably a central, wide and straight vein such as the median cubital vein.

 

Another pre-requisite for being recruited as a platelet donor is having an adequate platelet count which is tested for by performing a blood test (Complete Blood Count – CBC) at our Donation Centre.

 

Due to the nature of the requests for single donor platelet components (which usually cannot be planned ahead since it depends on patients’ needs), these donors have to be available to attend a donation session on demand. Another reason why donors are called in at such short notice is that the shelf life of platelet components is only of 5 days (making it impossible to stock up on these types of donations).

    

Males vs. females: Females who have ever been pregnant are not recruited as SDP donors. During pregnancy, certain proteins (called antibodies) may be formed and while these cause no harm to the woman, they should not be passed on to other patients via a transfusion. For this reason, NBTS would have more male SDP donors on the panel. 

 
Previous transfusion: The antibodies mentioned above can also potentially develop after a transfusion, thus donors who have been previously transfused are also not recruited as SDP donors.

 

The apheresis procedure takes longer than a WB donation. Our SDP donors are very dedicated to the service and to our patients because they are willing to undergo the procedure at any time this is required.

 

How safe is platelet donation?
The procedure of platelet donation is a very common one and is performed nearly every day (according to demand). The risks to the donor are negligible: our staff is highly trained to ensure donor comfort and safety (this starts right from the beginning when a donor is recruited); the machine used for collection is equipped with very sensitive detectors and monitoring parameters (again ensuring donor safety); and finally, as with all our practices at NBTS, the platelet collection set is sterile and disposable (being only used once).