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 once: 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).