In this issue of TRANSFUSION, McDonald and colleagues1 provide convincing evidence supporting an effective culture procedure to make platelets (PLTs) acceptably safe from bacteria up to 7 days without secondary testing or pathogen reduction. The National Health Service Blood and Transplant (NHSBT) of the United Kingdom transfused 1,230,029 PLT units (stored up to 7 days). There were no septic transfusion reactions (STRs) from 960,470 apheresis PLT (AP) transfusions and one STR from 278,559 buffy coat PLTs (BCPs). The report demonstrates the feasibility of implementing large-volume cultures of final PLT units in both aerobic and anaerobic bottles without adversely affecting PLT availability and provides ideas to improve PLT safety in the United States.

The NHSBT outcomes are truly outstanding. Comparison to American experience is difficult because of differences in practice (see below), but illuminating, nevertheless. The American Red Cross (ARC) reports outcomes from more than five million AP transfusions.2-4 From 2004 to 2006 ARC performed primary screening utilizing approximately 0.9% of PLT volume more than 24 hours after collection and used some collection kits without an inlet line diversion pouch. The STR rate was 13.3 per million (95% confidence interval [CI], 8.2-20.6) and the fatality rate was two per million (95% CI, 0.4-5.86; 20 STRs, three fatalities, 1,496,134 APs).2 From 2007 to 2011 the STR rate was 9.4 per million (95% CI, 6.6-12.8) and the fatality rate was 0.98 per million (95% CI, 0.27-2.5) utilizing approximately 1.8% cultures at more than 24 hours and exclusively kits with a diversion pouch (4,063,371 APs associated with 38 STRs and four fatalities).4 The Passport study used approximately 1.8% cultures, but collections were screened with 4 mL in both aerobic and anaerobic bottles 24 to 36 hours after collection and PLTs were stored up to 7 days. The STR rate was 20.6 per million (95% CI, 10.6-35.9; approx. 583,355 APs, 12 STRs, zero fatalities). Three Passport STRs were from Day 6 PLTs.5 In contrast, the NHSBT STR rate was 0.8 per million (95% CI, 0.02-4.5; 1,230,029 units, one STR, zero fatalities;1 see Table 1).

Table 1. How do collection device, culture time, culture volume, and bottle type influence bacterial safety?

Study	Collection device	Time (hr)	Bottles	% Cultured	PLT shelf life (days)	STR/million
ARC²	Predominantly Amicus	> 24	Aerobic	∼0.9	5	13.2
ARC4	Predominantly Amicus	> 24	Aerobic	∼1.8	5	9.4
Passport5	Trima and Amicus	24-36	Aerobic, anaerobic	∼1.8	7	20.6
Blood Systems9	Predominantly Trima	24-30	Aerobic	∼1.8	5	4.5
Blood Systems9	Predominantly Trima	24-30	Aerobic	∼3.5	5	0
Blood Systems11	Predominantly Trima	24-30	Aerobic	≥3.8	5	0
NHSBT1	Whole blood, buffy coat	36-48	Aerobic, anaerobic	∼5	7	3.6
NHSBT1	Trima	36-48	Aerobic, anaerobic	∼7	7	0

Three APs were returned to NHSBT from hospitals because of clumping in the bag. Each was contaminated with Staphylococcus aureus (2.4 contaminated units/million).1 It is inappropriate to use the near misses in the study by McDonald and colleagues for comparison to ARC and Passport data, because the latter studies do not report a comparable figure for suspect units returned to the donor center. It is known with certainty, however, that some contaminated units were distributed in addition to those recognized as causing STRs.2-5 Jacobs and coworkers6 and Hong and coworkers7 using sensitive active surveillance at the point of transfusion demonstrated the presence of 384 per million and 291 per million contaminated units, respectively, in addition to those causing transfusion reactions. (It should be mentioned that point-of-transfusion cultures, as performed by Hong and coworkers, were not used to interdict units, merely to detect contaminated units.) In both studies, all PLTs were screened with not more than 1.8% of the collection volume cultured and up to 50% of the PLTs were supplied by ARC.

Why did the NHSBT achieve a greater risk reduction after introducing prestorage quality control bacterial culture than the ARC? The ARC documented approximately a 70% reduction in reported STRs before and after culture, but McDonald and colleagues now describe more than a 90% reduction.1-3 The NHSBT procedure is to inoculate approximately 5% of BCP and approximately 7% of AP volumes, culture at 36 to 48 hours, utilize aerobic and anaerobic bottles, and collect with the Trima apheresis device. The NHSBT cultures 16 mL from each final PLT unit (BCP mean, 310 mL; AP mean, 243 mL).1 The ARC procedure is to culture approximately 1.8% of AP volume, inoculate at 24 hours, use only aerobic bottles, and collect primarily with the Amicus apheresis device. The ARC (and most American centers) cultures 8 mL from the mother bag (mean, approx. 450 mL) whether the collection is a single, double, or triple PLT collection.3, 4

Large-volume cultures for primary screening

In 2009 after demonstrating a 54% increase in the confirmed positive rate by moving from 4- to 8-mL inoculations for primary screening, Eder and colleagues3 stated, “The clear and compelling relationship between culture volume and test sensitivity demonstrated in this report strongly suggests an opportunity to further maximize current testing sensitivity, especially for high-volume donations, either by testing 8 mL from each component prepared from a single donation or by increasing sample volumes to 16 to 20 mL from the original collection volume.” In addition to Eder, Souza, Bravo, Jenkins, Kamel, and Delage and colleagues3, 8-12 have also demonstrated that increasing the volume inoculated increases the rate of confirmed positive primary screening results in their organizations, indicating that larger-volume cultures remove more contaminated units from the transfusion pool. Bruhn and coworkers13 had shown a significant result in a meta-analysis of three of these studies.

Assessing the clinical impact of large-volume cultures is difficult because most studies are small and there is little consistency in methods. However, aggregating multiple studies demonstrates the benefit of large-volume testing. Twelve studies utilizing not more than 8 mL (1.8%) have together yielded a STR rate of 10.7 per million (95% CI, 8.6-13; 96 STRs, approx. 9,005,878 PLT units).2, 4-10, 12, 14-16 On the other hand, seven studies utilizing more than 8 mL found a STR rate of 1.7 per million (95% CI, 0.3-4.9; three STRs, approx. 1,943,173 units; p < 0.0003).1, 9, 11, 12, 17-19 This comparison is crude because in some studies, components issued is estimated based on split rate. There is some overlap in reporting and manufacturing methods, culture time, storage medium, culture techniques, definitions of results, and so forth varied. Nevertheless, there is an indication that large-volume cultures reduce the frequency of STRs.

Delayed primary screening

Delayed screening improves safety because 1) there is an unpredictable, variable delay before bacteria in a contaminated PLT unit begin rapid growth and 2) it takes more time for a contaminated unit to reach clinically significant concentrations of bacteria than to become detectable by culture.

One growing organism in a 450-mL PLT unit requires 25.3 generations to reach a concentration of 100,000 bacteria/mL, which might cause a transfusion reaction.7 Because generation times of pertinent organisms are from 1 to 4 hours, a typical organism would have to begin rapid growth 25 to 101 hours before transfusion to cause a reaction but would only have to grow for 5.1 to 20.5 hours to have a 75% chance of being detected by a 3.8% culture. A 3.8% sample would detect such a contaminated unit 1.1 to 4.5 hours earlier than a 1.8% sample depending on the contaminant's generation time.20

A negative culture at 24 hours may not indicate true sterility because there could be organisms which have not grown to a sufficient concentration to be detectable. With each additional hour before culture, the chance that organisms become detectable increases. The data of McDonald and colleagues suggest that nearly all organisms begin to grow within 36 to 48 hours of collection and that a negative culture at that time indicates improved transfusion safety. Delage, at Héma-Québec, has presented data that support the beneficial impact of testing at 48 hours utilizing the same sample volume. After testing 23,188 units, a 29% increase was observed in confirmed positive primary culture tests at 48 hours versus 24 hours. In addition, before culturing at 48 hours, the rate of positive surveillance cultures at outdate was 253 per million (5/19,801) and since delayed culture there have been no positives in 2400 cultures.12

Three studies of about 50,000 collections each using 15 to 20 mL (in aerobic and anaerobic bottles) with early primary testing (before 24 hr) yielded higher adverse reaction or expiry culture rates than would be expected based on the volume of the initial culture.17-19

While it is difficult to isolate and quantify the impact of delayed testing from published studies, the rationale is clear and the data of McDonald and Delage indicate that delayed testing increases sensitivity and increases the chance that a negative unit is transfusion safe. A downside of delayed culture is that the shelf life is shortened by the amount of delay in testing.

Anaerobic bottle

In the United States, there has been reluctance to use anaerobic bottles because of PLT loss with greater volume cultured, increased false-positive results, and cost.3 Even though some positive results with the anaerobic bottle have been noted, most US blood centers still do not use the anaerobic bottle.5, 21 The anaerobic bottle is used abroad (P. Flanagan, personal communication, June 2016; J. Pink, personal communication, August 2016; D. de Korte, personal communication, September 2016).1, 12, 17-19 McDonald and coworkers report that 66% of the confirmed positives were anaerobic-bottle-only results, indicating the clinical advantage of a shorter time to reactivity with the anaerobic bottle.5, 22-25 In addition, the anaerobic bottle covered a broader range of organisms. Unfortunately, McDonald and coworkers removed negative-to-date bottles from the incubator once one bottle of the sample was positive. For the 267 anaerobic-only positive tests, one does not know whether or when the associated aerobic bottles would have become positive. While the rate of false positives and costs are higher with the anaerobic bottle, this could be acceptable when compared with the cost, logistic difficulty, regulatory impact, and high false-positive rate of secondary testing and the cost, loss of PLT production, logistic difficulty, and damage to PLTs inherent in current pathogen inactivation treatment.6, 26, 27

Collection device

Eder and coworkers2, 3 first reported a relationship between the collection device, STRs, and rates of contamination at collection (A. Eder, personal communication, October 2014). Bravo and colleagues9 subsequently confirmed that Amicus produces PLTs that have a higher rate of contamination than PLTs produced by the Trima as detected by the BacT/ALERT test. Townsend and coworkers28 reported a surveillance test study of PLTs produced by Amicus and Trima, which suggested a trend toward a higher rate of confirmed bacterial contamination on Day 7 with the Amicus than with the Trima. Wu and colleagues29 spiked large volumes of blood with bacteria. It was found that Trima processing yielded concentrations of Staphylococcus epidermidis and Bacillus cereus that were 1 to 2 logs lower in the final PLT bag than in the unprocessed blood, but that for Escherichia coli, the concentration was the same. In 2007 and 2009, the ARC showed STR data with the Trima, Amicus, and Spectra, but it was not possible to confirm a significant device impact on the rate of STRs.2, 3 It is important to analyze more recent ARC STR data to confirm the probability of a higher bacterial risk with the Amicus compared to the Trima.

Unfortunately, there are too many variables to quantify the relative contribution of each of the four factors to the improved safety achieved by the NHSBT. Table 1 summarizes data from some large studies and, while trends are evident, it reveals the difficulty in isolating the impact of delayed and large-volume culture.

SUMMARY

American blood centers should use large-volume primary screening. Culture of something less than 7% of AP volume (NHSBT method) might be sufficient. For example, increasing the current sample size from approximately 1.8% to at least 3.8% and screening at 24 to 48 hours is likely to achieve bacterially safe 5-day APs and using an at least 3.8% sample at 48 to 72 hours should achieve bacterial safety for 7 days for those clinicians willing to tolerate the decreased function of extended storage.11 There is insufficient evidence to recommend routine use of the anaerobic bottle at present.

The Food and Drug Administration (FDA) has encouraged licensed establishments and hospitals to improve PLT safety.26 It has concluded that an approximately 1.8% culture is not sufficient for 5-day safety based on ARC predominantly Amicus data.2-4 Large volumes and delayed screening have been approved and used abroad (P. Flanagan, personal communication, June 2016; J. Pink, personal communication, August 2016; D. de Korte, personal communication, September 2016; M. Goldman, personal communication, February 2017).1, 12, 17-19 Unfortunately, NHSBT and Héma-Québec data were not available to the FDA for its Draft Guidance.1, 12 The current FDA document does not describe a distinct option utilizing large sample volumes and delayed primary screening. The method used by NHSBT should stimulate reevaluation by FDA of its recommended strategies, especially since the NHSBT PLTs at 7 days (0.8 STR/million; 95% CI, 0.02-4.5) are safer than PLTs found negative in an approved secondary test (Verax) with 5-day storage 73 per million (95% CI, 9-263).1, 6

Using large-volume and delayed cultures will improve patient outcomes and inventory management with lower cost and less hospital disruption than secondary testing and current pathogen reduction. Assuming the FDA encourages the use of large volumes and delayed testing, there should also be studies to further assess the value of the anaerobic bottle and to assess whether similar safety measures are necessary with both the Amicus and the Trima because of the probability that collection devices influence the rate of STRs.

ACKNOWLEDGMENTS

The author acknowledges the counsel provided by Michael R. Jacobs, MD, PhD, Mark E. Brecher, MD, Hany Kamel, MD, and Marjorie Bravo, MD, MPH, in preparing the manuscript.

CONFLICT OF INTEREST

The author was a consultant for bioMérieux and Terumo, but declares no conflict of interest.

Peter A. Tomasulo, MD
e-mail: [email protected]
Blood Systems
Scottsdale, AZ

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Citing Literature

Volume57, Issue5

May 2017

Pages 1099-1103

Reducing the risk of septic transfusion reactions from platelets

Large-volume cultures for primary screening

Delayed primary screening

Anaerobic bottle

Collection device

SUMMARY

ACKNOWLEDGMENTS

CONFLICT OF INTEREST

REFERENCES

Citing Literature

References

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Reducing the risk of septic transfusion reactions from platelets

Large-volume cultures for primary screening

Delayed primary screening

Anaerobic bottle

Collection device

SUMMARY

ACKNOWLEDGMENTS

CONFLICT OF INTEREST

REFERENCES

Citing Literature

References

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