Management of blood donors
with a low level of exposure to variant Creutzfeld-Jacob
disease
Daniela Pasqualetti,@ Alessandro
Ghirardini,* Rino Bellocco,# Stefania
Vaglio,@ Maria Gozzer,@ Gabriella
Girelli@
@ Blood Bank, Dipartimento di Biotecnologie
Cellulari ed Ematologia, University "La Sapienza", Rome, Italy (D
Pasqualetti, S Vaglio, M Gozzer, G Girelli); * Laboratory of
Epidemiology and Biostatistics, Istituto Superiore di
Sanità Rome, Italy (A Ghirardini); #Department
of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden.
Correspondence: Daniela Pasqualetti. E-mail: pasqualetti@bce.med.uniroma1.it
Prevention of hypothetical transmission of new variant
Creutzfeldt Jacob Disease (vCJD) through blood transfusion has
been the deferral from donation for those who stayed in UK or
France for more than six months, and/or the adoption of
leukoreduction. We suggest an approach also for people with a
length of stay less than six moths, by the adoption of a protocol
of multicomponent apheresis, with the donation of two red blood
cells units submitted to an on-line filtration, without plasma and
platelets collection. Risk of transmitting vCJD leaded several
countries to modify their policies regarding blood safety. US,
Canada and New Zealand deferred blood donors who lived in UK and
France for more than six months during 1980-1996, as a proxy of
the exposure to contaminated beef. This exclusion from donations
produces an expected drop in the blood supply, from 1% to 2.5%
depending on the estimates.1,2 No policy was chosen for
donors with a level of exposure (less than six monhs), even if the
US Red Cross has recently proposed their exclusion from donation,
with an additonal drop in the blood supply. Other countries, such
as Canada, France, Portugal, Ireland and Switzerland recommended
and implemented universal leukoreduction,3 for removing
the possible source of prion infectivity. UK also introduced
leukoreduction together with the discard of plasma, which
infectivity could not be affected by leukoreduction.4
An important issue in the debate on the hypothetical risk of vCJD
transmission by blood5 concerns with the efficacy of
leukoreduction6 in the removal of some possible sources
of prion proteins, other than leukocytes, such as platelets and
plasma. In fact red blood cells (RBC's) which is submitted to the
standard leukoreduction process contains some amount of platelets
fragments as well as plasma: for this reason it has been suggested
that the currently leukoreduction techniques could not be as safe
as possible to reduce the theoretical risk of vCJD transmission.
This suggestion is based on some experiments7 showing
that the prion protein (PrP) is expressed on leukocytes, but also
in high concentration on platelets and plasma. If the rationale
for the leukoreduction is the removal of cell expressing PrP
(either in the normal form or in the form causing vCJD), the
presence of discrete amounts of platelets and plasma in RBC's
after the standard leukoreduction procedure could represent an
additional risk. A way of production leukoreduced RBC's together
with the removal of platelets and plasma, is represented by the
multicomponent apheresis procedure with an in-line
leukoreduction.8 This technique allows for the
selective donation of each blood component, namely RBC's, which is
produced in a standardised way and with high levels of purity. The
adoption of a targeted protocol of leukoreduction applied to the
"multicomponent apheresis", for people with a low level of
exposure (less than 6 months in UK), could allow the flexibility
to collect standardised blood components from a single donor, in
one step, at the time of donation, with the availability of high
quality leukoreduced RBC's, with an on-line filtration. Plasma
will not be collected, eliminating any theoretical risk of
infectivity for vCJD, and a frequent plasma programme by apheresis
will cover this plasma deficiency. Moreover by evaluating
platelets with Thoma's camera, a low level of platelets may be
counted, corresponding to a 1-log estimated reduction of platelets
concentration in comparison to standard leukoreduced RBC's. On the
basis of the precautionary approach9 we believe the multicomponent
apheresis a way of production standardised RBC's with the highest
rate of purity with regard to platelets and plasma, thus further
reducing the theoretical risk of vCJD transmission by blood
transfusion.
