Validation testing for pH tesing of platelets as a surrogate test for bacterial detection

1
VALIDATION TESTING FOR pH TESTING OF PLATELETS AS
A SURROGATE TEST FOR BACTERIAL DETECTION MacDonald
, A., Evanovitch, D., Wilcox, L., Lester, C.,
Boychuk, D., Blajchman, M.A. Hamilton Regional
Laboratory Medicine Program (HRLMP), Hamilton
Health Sciences and St. Josephs
Healthcare Hamilton, Ontario
PURPOSE
RESULTS
TEST RESULTS (Validation Testing) Table 1.
Results of Validation Testing
To validate the use of the IQ 125 pH meter as a
surrogate test for the detection of bacterial
contamination of whole-blood-derived PRP and
apheresis platelets for transfusion.
BACKGROUND
Bacterial contamination of blood and blood
products is both an under-recognized and
under-reported cause of transfusion-associated
morbidity and mortality. In fact it is quite
likely that bacterial sepsis due to the bacterial
contamination of blood products is currently the
leading microbiological cause of transfusion
related morbidity and mortality. In light of such
issues the American Association of Blood Banks
has enacted a standard that requires the blood
Transfusion Services in the US employ methods to
limit and detect bacterial contamination of all
platelet components.
Figure 1. Bacterial Growth in Test Platelets
Figure 2. pH lt7.0 in Test Platelets
In the second phase of the study, 100 platelets
had pH testing performed. Only one unit tested lt
7.0. The platelet unit was removed from inventory
and sent to Microbiology for culture. No growth
was noted after five days of culture.
DISCUSSIONS AND CONCLUSIONS
METHODS
Although apparent false negatives were observed
in the first phase of validation and one false
positive was observed in the second phase, pH
testing appears to be a fairly good indicator of
bacterial growth in platelets. Based on the
results of the validation testing, the IQ 125 pH
meter was implemented as a surrogate test for the
detection of bacterial contamination in platelet
products. The testing is performed immediately
prior to issue for transfusion. This testing is
being used in conjunction with the Canadian Blood
Services direct culture of apheresis platelets.
The expectation is that the introduction of
surrogate pH testing for bacterial contamination
will improve blood product safety for patients
receiving platelets.

• Phase 1
• The first phase of validation study involved the
  evaluation of PRP platelets obtained from the
  Canadian Blood Services. All platelets were four
  days old on arrival. Each platelet bag was
  divided into two aliquots, using a sterile
  docking device in order to maintain a closed
  system.
• One aliquot served as the control.
• The second aliquot represented the test platelet
  product.
• Test platelets were inoculated with 0.1 mL of a
  bacteria suspension containing 10 to 100
  colony-forming units (cfu). Various strains of
  bacteria were used for this validation. A sample
  from each bag was sent to Microbiology for
  culture. The pH testing and culture were examined
  for four consecutive days on each platelet unit
  (control and test).
• Phase 2
• The second phase of the validation study included
  the testing of 95 PRP and five apheresis
  platelets from the hospitals inventory. This
  phase was included to look at the rate of false
  positive results with the IQ 125 pH meter.
  Platelets with pHs less than 7.0 were considered
  potentially contaminated and were sent to
  Microbiology for culture.

ADDITIONAL DATA
To date approximately 1500 units of platelets
have been tested, Of which 13 had a pH below 7.0.
One was culture positive (Staphylococcus species,
coagulase negative).
ACKNOWLEDGEMENTS
Twenty platelets tested but one was not valid due
to bacterial growth in both test-1and control-1
Special thanks to the MUMC Transfusion Medicine
Technologists for their continued support of this
study.