Members of the Blood Products Advisory Committee to the Food and Drug Administration convened for their 105th meeting in Rockville, Md., on Dec. 4-5 to advise the FDA on two issues: labeling of red blood cell units with historical antigen type results, and performance data considerations for infectious disease assays used to screen organ donors.
Labeling of Red Blood Cell Units with Historical Antigen Typing Results
Blood establishment practices for providing what is known as "historical" RBC antigen typing results with current donations was discussed by BPAC, FDA and industry representatives. The antigen testing under deliberation is for non-ABO red cell antigens and methodologies used are serology (licensed and unlicensed reagents) and molecular (assay use is investigational). Provision of results by blood centers from current testing and testing performed by hospital blood banks and transfusion services was not the focus of the BPAC discussion. Among blood centers, different processes have developed for providing the results — indicated as historical — to transfusion services, such as shipping invoices, separate documents included with the blood shipment, and tie tags.
Jennifer Jones, MBA, CMQ/QE(ASQ)CQA, Division of Blood Applications, Office of Blood Research and Review, Center for Biologics Evaluation and Research, FDA, provided an overview to the committee of the various processes used in blood centers and transfusion services for collecting the blood product, pre-transfusion testing, searching for antigen-negative blood, and crossmatching a recipient sample with the antigen-negative unit. Blood collection processes include identification of the donor at presentation, use of a unique donation identification number linking the donor to the donation to ensure tracking and traceability, implementation of processes to look for duplicate donor records, ABO/Rh typing, and a review of the donor's history searching for any test results or medical history that may impact the current donation. Routine pre-transfusion testing includes procedures to detect clinically significant RBC antibodies and is generally performed in time to provide blood that lacks the corresponding antigen(s). The transfusion service will request antigen-negative units from the blood center if the service determines it does not have any, or enough, units in inventory. There is no (FDA) requirement for the transfusion service to reconfirm the antigen types on the units received. The antigen-negative unit(s) must be crossmatched with the recipient; electronic crossmatching is not allowed.
Testing at the time blood is needed has several associated challenges, including that it is time-consuming, expensive and labor- and resource-intensive. It also is difficult to complete in emergency situations and antisera may be unavailable.
Use of historical antigens — an alternative practice — would allow U.S. blood centers to select RBC units from inventory that have a record of antigen typing results from previous donations (historical results) without performing testing on the current donation. The transfusion service may or may not confirm the antigen typing on the current unit. This practice is typically based on two test results on record at the blood center. Jones reported that an AABB workgroup has been established with FDA liaisons to review current practices and develop a protocol based on consensus practice to be considered for future use. Practices in several other countries were noted: Canada, Australia and Israel make extensive use of ISBT 128 labeling for the historical results, and the Netherlands, Austria and Hong Kong require testing on at least two donations before making use of historical results.
The FDA viewpoint on potential benefits and risks of labeling using only historical antigen results includes:
- Supports transfusion facilities in emergent situations and chronic transfusion programs by having "pre-selected" units for compatibility testing
- Potentially reduces errors if units have been tested more than once
- Saves time and resources
- Conserves antisera and other reagents that are often in limited supply
- Hemolytic transfusion reaction if a unit(s) is mistyped or mislabeled
Louis M. Katz, MD, executive vice president, America's Blood Centers, provided an overview of historical RBC antigen practices among ABC members. ABC members provide antigen-negative units for 1) patients with clinically significant alloantibodies, 2) patients at risk for but not yet alloimmunized, such as individuals chronically transfused for illnesses like sickle cell disease, and 3) transfusion services that are reluctant to incur costs and delays as well as maintain staff required for repeated testing of previously typed donors. Katz described the basic process at the blood center: eligible units have one or more prior donations that have been tested with licensed (or unlicensed) reagents; results are archived electronically (LIS and/or BECS); when units are requested subsequent donations (currently in inventory) are identified and selected based on relevant negative antigens. Transfusion services may or may not confirm results depending on their capability and availability of antisera. ABC surveyed its members (~71 percent response rate) to gather data on current practices related to historical antigen typing and provision of results to the transfusion service. Respondents included a broad range of center sizes and geographical distribution. Among surveyed individuals, 43.4 percent said they do not report results of historical antigen typing. Katz noted that the respondents in this category were of varying center size. Facilities reported a variety of schemes in use as the minimum testing required for antigen-negative designation: a mixture of molecular and serology, licensed serology, or licensed or unlicensed serology. Sixty percent report the results using a tie tag and the remaining 40 percent have made use of detached documents. Data were shared showing a marked reduction in false-negative antigens reported by blood centers in recent years with 2012 looking to have a 99.4 percent compliance rate. ABC centers requested that the FDA consider an immediate route (cGMP compliant) for provision of these test results using integral labeling and the value of the ongoing AABB workgroup to reach a consensus on the definition of "historically negative."
Lynne Uhl, MD, director, Laboratory and Transfusion Medicine, Beth Israel Deaconess Medical Center, provided a transfusion service perspective on the use of antigen-typed red cells. Uhl noted that approximately 3 percent of their transfused patients form alloantibodies with the potential for some alloimmunization scenarios becoming quite complicated. She reiterated what other speakers had said concerning prophylactic matching of phenotypes for some hemoglobinopathies such as sickle cell disease to reduce rates of alloimmunization and prevent delays in getting units which otherwise might occur in cases of new antibody formation. She also provided information about prophylactic antigen matching that is practiced in other countries (e.g., the United Kingdom and the Netherlands) for women of child-bearing age. Additionally, Uhl explained the difficulties of providing compatible blood for recipients with panreactive warm autoantibodies and the use of prophylactic antigen matching to mitigate this risk for alloimmunization. At Beth Deaconess approximately 1,057 antigen-negative units have been received into inventory in the first three quarters of 2012 with just more than 12 percent being typed for four to six antigens. The units have current results attached via a tie tag; any testing performed by the transfusion service is to screen for additional units. Even with this limited use of antisera it consumes 11 percent of the reagent budget in the transfusion service — approximately $53,000 per year. Uhl summarized opportunities for labeling of red cell units based on historical phenotype (or molecular typing) to offer:
- Enhanced delivery of appropriate red cell components to patients in times of urgent need
- Reduction in duplicative testing between the blood center and transfusion service
The acceptability of labeling of red cells with historical serologic or molecular antigen types is enhanced with testing performed on two separate donations, assurance of robust processes in place to connect historical records with current donations and use of ISBT 128 labeling to promote electronic scanning of results.
Gregory A. Denomme, PhD, director, Immunohematology and Transfusion Services, BloodCenter of Wisconsin, reviewed the red blood cell genotyping experience in the blood bank setting. Genotyping, the process that combines DNA with different reagents to detect single nucleotide polymorphisms (SNPs), has been applied to donor testing to address gaps in phenotyping. The methods use synthetics reagents and overcome some issues prevalent in serological studies. RBC genotyping is not affected by weak antigen expression and can detect altered antigens that are otherwise problematic. Denomme summarized his thoughts on labeling of blood from historical data: use of two historical phenotypes, or genotypes, or one of each is an accurate and safe practice when performed on determinations from two separate blood donations.
Mindy Goldman, MD, Canadian Blood Services, described processes for providing antigen-negative units and clinical uses for the products that were very similar to her U.S. counterparts. She noted use of ISBT 128 for integral labeling — as previously reported by Jones — and added that there is no requirement for hospitals to retype current or historical types. The majority of the results are obtained using licensed reagents; tie tags or letters are the method of communication when use of unlicensed reagents or genotypes are being reported.
Rebecca See, MS, MLS(ASCP)CM, CQA(ASQ), deputy director, Regulatory Affairs, AABB, reviewed for the BPAC the origin and ongoing commitment of the AABB workgroup established to review historical antigen labeling processes currently in use by blood centers. The group is also charged to develop a protocol that would provide an acceptable mechanism for multiple establishments to use. The workgroup was established following discussions with FDA representatives at the spring 2012 meeting of the AABB FDA Liaison Committee. Small surveys of blood centers and transfusion services were conducted to obtain a sampling of variance in practices among the institutions. See reported data similar to other speakers: use of tie tags as well as detached documents by blood centers and some transfusion services accept historical types and some of these reconfirm the types while other do not. The ongoing projects of the workgroup are as follows:
- Reach consensus on a definition of "historically negative"
- Consider options for communicating the test results to the transfusion service
- Integral labeling is consistent with cGMP
- Use of unlicensed reagents must be noted
The workgroup has considered issues such as appropriate processes to link historical donor records to current donations, including properly identifying the donor at presentation and potential impact of failures in these processes. The conclusion of the group is that current processes being used for other donor testing (ABO/Rh, antibody screening and infectious disease screening) have proved to be robust and do not require further validation. Customer expectations, as relayed to members of the workgroup, are that testing is the responsibility of the blood supplier and that the transfusion service wants results clearly communicated and attached to the unit, and to know when unlicensed reagents were used to obtain the results. Also, the transfusion service does not want to be required to confirm the historical result. Workgroup results/proposals will be shared within AABB and with the FDA.
In the open public hearing, AABB, the American Red Cross and New York Blood Center strongly encouraged the FDA to enable integral labeling of units with the test results. ARC and NYBC specified criteria that could be used to define historically negative antigen results. The joint statement prepared by AABB, ABC and ARC deferred to the upcoming recommendations expected from the AABB workgroup; ARC and NYBC are among the organizations participating in the workgroup.
Committee Discussion of Questions Posed by FDA
The following questions framed the committee discussion:
- Please comment on the effectiveness of the following practices to mitigate the risks related to historical antigen typing.
- Reporting such information on the basis of historical RBC typing results from two separate donations.
- A validated process to confirm donor identification and accurate linkage of the current RBC donation to the historical results.
- Confirmation of relevant negative antigen results on the current unit prior to transfusion, when feasible.
- Please comment on whether your responses to the first question would vary if serologic or molecular testing, or both, are performed.
Committee members seemed to reach a consensus that concordant results from two separate donations is a reasonable expectation before reporting results on subsequent donations as historically negative, and did not indicate a preference for serologic or molecular methodologies. The committee asked questions of FDA and industry representatives to gain a better understanding of the concerns related to donor identification and accurate linkage of a current donation to any historical results and the processes in place at blood centers to address these issues. The committee agreed that the issue of donor linkage is important, but has a broader scope than the current discussion. The committee then noted — with the understanding that establishment standard operating procedures include processes to address donor identification and accurate linkage — that the systems in place at blood centers appeared to be adequate and functioning appropriately. There was agreement that there should be no requirement for transfusion services to reconfirm the result reported from blood centers, with several members stating a strong opinion that the transfusion service should not be required to repeat any testing other than ABO (and Rh when negative). Additional comments by the committee included support for use of integral labeling to provide any specific information related to the unit, with many indicating a preference for use of ISBT 128 so that the information can be on the face label.
Performance Data Considerations for Infectious Disease Assays Used to Screen Organ Donors
The FDA sought advice from the committee on performance data considerations for organ donor screening indications. Laura St. Martin, MD, Division of Human Tissue, Office of Cellular, Tissue and Gene Therapies, CBER, provided an overview of the topic. The Health Resources and Services Administration (HRSA) oversees the transplantation of human organs; organ donor testing policies are established by the Organ Procurement and Transplantation Network (OPTN) under a contract administered by HRSA. However, the FDA is responsible for the evaluation of infectious disease assays used to screen organ donors (in addition to regulating assays for blood and tissue donors and diagnostic tests). To date, organ donor screening indications have been granted based on data from studies supporting blood donor screening indications. To address the needs of the transplant community, the FDA would like to augment this historical path to obtaining an organ donor screening indication. For instance, what data might be required when sponsor is developing a novel assay for organ donor screening and does not intend to pursue a blood donor screening indication. Additionally, what type of data would be required if a sponsor is developing a diagnostic assay and would like add the organ donor screening indication.
To offer additional clarity on organ donation, St. Martin provided an overview of types of organ donors (living or deceased — either after neurologic or circulatory death) and clarified that the discussion would be focused on performance of assays when used to test deceased potential organ donors. She also acknowledged there may be potential physiological changes that occur after brain death such as catecholamine storm, hormonal changes, and elevated cytokine and other inflammatory markers that may affect assay results. St Martin also discussed some of the differences in the blood donor and organ donor populations. For comparative purposes, there are about 10 million blood donors (donating 25 million units of blood each year) while there are about 8,000 organ donors (donating 22,000 organs each year). It was noted that the organ donor pool is relatively inelastic. This inelasticity is attributable to the fact that there is a finite number of obtainable organs from a single donor; there are no opportunities to obtain additional organs at a later time; and the number of donors and donations has changed little over the past decade. St. Martin also noted infectious disease (namely, HCV and HIV) incidence and prevalence rates are higher in the organ donor population compared to the blood donor population. She attributed this to the pre-screening that occurs when blood donors are asked directly about risk factors for communicable diseases. Potential challenges that may arise when pursuing organ donor screening indications include, but are not limited to, sample sizes for clinical studies, verifying a true positive, and hemodilution.
Karen Near, MD, MS, Division of Transplantation, Health Systems Bureau, HRSA, provided an overview of the organ donor and transplantation system. The summary included descriptions of the role of the federal government in transplantation, legislative framework surrounding organ transplantation and overviews of the key players in the field. Near reiterated the fact that HRSA oversees the transplantation of human organs and that OPTN, under contract, is responsible for the development of the policies that govern the allocation of donated organs, organ donor testing, and the collection of transplant data in the U.S. OPTN carries out many of the duties in partnership with the United Network for Organ Sharing. OPTN Policy 2 addresses the minimum procurement standards for an organ procurement organization. Near highlighted the fact that under OPTN Policy 2.2.3, "Screening Potential Organ Donor," all potential organ donors must be tested by use of a serological screening test licensed by the FDA for Anti-HIV-1 and Anti-HIV-2 (Policy 220.127.116.11) and the transplantation of an HIV-positive organ may not knowingly be performed (Policy 18.104.22.168). The requirements for donor evaluation are in Policy 2.2.4, which states "all donor laboratory testing must be performed in an appropriately accredited laboratory utilizing FDA-licensed, approved, or cleared serological screening tests." In the event that a required screening test is not commercially available prior to transplant, an FDA-licensed, approved or cleared diagnostic test is permissible. However, a diagnostic screening test is not acceptable for Anti-HIV. Additionally, all deceased donors are screened for the following infectious diseases, as required in Policy 22.214.171.124:
- FDA-licensed Anti-HIV I, II (diagnostic testing not acceptable)
- Hepatitis screen serological testing; including HBsAg, HBcAb and Anti-HCV
- VDRL or RPR (FDA-approved diagnostic tests are acceptable)
- EBV serological testing
Paul Mied, PhD, deputy director, Division of Emerging and Transfusion Transmitted Diseases, Office of Blood Products Research and Review, CBER, presented perspectives on assay performance for blood donor screening. A comprehensive summary of the required blood donor screening tests and their pathway for regulatory implementation was reviewed. Mied provided an overview of pathway to licensure for blood donor screening assays. The basis for licensure of a blood donor screening assay is collecting data under an IND to demonstrate the product is safe, pure, potent (as claimed), and the manufacture is performed under GMP conditions. The studies to support blood donor screening assay development fall into five different categories:
- Analytical sensitivity studies are preclinical studies designed to measure a specific target analyte;
- Analytical specificity studies are preclinical studies to assess cross-reactivity and interference;
- Other preclinical studies that might include sample integrity, shipping stress, carryover and stability studies;
- Clinical sensitivity studies are conducted in the intended population, generally from three geographically different and diverse centers; and
- Clinical specificity studies are undertaken to determine the rate of false positives and typically include 10,000 or more random blood donor samples.
Once adequate supporting data are available, the sponsor may submit a BLA, which, if approved, would lead to eventual licensure. Furthermore, once a blood donor screening assay is licensed, post-marketing surveillance also should be considered for the development of assays. FDA lot release panels are designed to assure continued assay sensitivity. Clinical sensitivity and specificity are generally very high with the 95 percent confidence interval lower bound well above 99 percent.
Jay Fishman, MD, associate director, Massachusetts General Hospital, Transplantation Center, presented considerations regarding an assay specifically for organ donor screening. High-level summaries of potential bacterial, fungal, parasitic, and viral donor-derived, transplantation transmitted information data were provided. Fishman noted some donor screening challenges included lack of standardization of testing assays (specific assays deployed), the impact of sample variability (sample dilution, use of screening versus diagnostic tests and window periods versus false positive assay results), no standard paradigms in place for evaluating and communicating all information relating to the donor, and lack of investigating post-transplantation adverse events of infections. The current organ donor screening tools include review of social history for high-risk behavior, blood and urine cultures, serology, PCR and antigen tests, and antibody tests. Fishman noted the importance of reducing the false-positive rate from any assay to prevent wastage of donated organs.
Committee Discussion of Questions Posed by FDA
Analytical Performance Data describe the quantitative and qualitative performance characteristics of an assay regardless of the ultimate intended use of the assay. Taking into account the theoretical possibility that physiologic changes after brain death may affect the performance of assays, please discuss the following with respect to analytical performance data:
- Whether there is any information of particular importance to assessing the performance of infectious disease assays used for testing organ donors that would not be obtained from the typical analytical studies performed for blood donor screening and diagnostic indications?
- In particular, are there specific studies that may be useful to address the theoretical possibility that physiologic changes after brain death may affect assay performance?
The committee discussed the need for additional scientific information on physiologic changes that may occur after brain death. Specifically, studies evaluating the effects of brain death on hemostasis and serology changes were discussed. It also was noted that different causes of death could be evaluated for potential differences. The need for a repository of blood and tissue samples was acknowledged and the potential for multiplex assay testing platforms also was discussed. However, in the absence of relevant scientific data, the committee suggested that preclinical interference studies that are scientifically justifiable, at least in theory, should be conducted to evaluate the performance of organ donor screening assays.
Clinical Performance Data describe the performance characteristics of the assay in the populations in which the assay is intended to be used. While specimens from populations other than the intended use population may be used to assess clinical sensitivity, as is done for blood donor screening assays, please discuss the use of specimens from populations other than the intended use population for conducting clinical specificity studies for organ donor screening assays. Please specifically discuss the following regarding clinical specificity studies:
- Potential challenges posed by various strategies, including performing a small study in organ donors (with resultant wider confidence intervals) vs. a larger study in alternate population vs. evaluating performance data from a combination of studies that includes both a study in organ donors and a study in an alternate population
- Potential challenges that may be encountered in determining the true result (positive result vs. negative result) of testing of a donor sample and ways those challenges may be addressed
As the blood donor pool is significantly larger than the organ donor pool, the committee acknowledged the potential challenges to conduct a clinical study in the organ donor population. Several members noted that the current approach to obtaining an organ donor testing indication is the most feasible approach because it would not be of financial interest to pursue an organ donor indication exclusively. If a sponsor were to develop an assay exclusively for the organ donor population, the committee stated some clinical data in the target population should be necessary, but clinical trial sizes should not be required of the size that is required for blood donor assays. However, it was noted that if the organ donor screening is pursued alongside a blood donor screening population, no additional clinical data should be required and that preclinical studies would be adequate. The committee also suggested that a stratified or tiered approach to obtaining an organ donor indication should be considered.
Thresholds for Performance Criteria are minimum acceptable levels for performance characteristics such as clinical sensitivity and specificity may vary based on the type of assay and the intended use. Decisions about thresholds might take into account risks associated with the particular infectious agent. Risk considerations might include:
- Whether the assay detects an organism that causes nonfatal or treatable diseases (e.g., cytomegalovirus) compared to another organism that causes serious or untreatable disease (e.g., rabies or lymphocytic choriomeningitis virus)
- Whether a positive result may be used to make decisions about the use of any of the donor's organs vs. used to guide decisions about recipient selection or treatment
What factors should FDA consider in making decisions about minimum acceptable levels for performance (clinical sensitivity and specificity) for assays used to test potential organ donors?
Given the difference in target populations of blood and organ donors, and test-to-test variability for different infectious diseases, the committee noted that thresholds for specificity and sensitivity would not be the same. It was acknowledged that confidence intervals for assays may vary depending on the environment in which the test is to be used (e.g. home use versus laboratory use) and the specific disease the assay is used to test. Considering the availability of organ donations, committee members also noted that the worst-case scenario is a false positive because it would lead to the discard of the organ(s). The desired conditions, if presented, would be an assay for the organ donor population that, when compared to a blood donor assay, is less sensitive but more specific. The sentiment expressed by several committee members was that the agency and sponsors should do the best they can to come to a balanced solution; a primary concern of the committee was "donors should not be excluded for reasons of failed testing."