Blood components, product modifications, and blood donor screening

Background

Transfusion of blood requires multiple steps, including blood donation from nonremunerated healthy volunteers, manufacture, testing, and modifications of blood components, and finally administration of the product to a patient. While blood donation and transfusions have steadily decreased in the United States over the past decade, 16 million blood products were generated by collection and about 15 million transfused in 2019. Red cells, platelets, plasma, and cryoprecipitate are manufactured using relatively simple and widely available methods to supply the demand for blood. The safety of the blood supply is ensured using donor history questionnaires, laboratory testing, and quality measures to keep these biologic products derived from millions of donors therapeutically consistent.

Content

The first half of the chapter describes the blood manufacturing process, beginning with the collection of whole blood or apheresis products from a healthy donor to the point where the product is ready to be transfused into a patient. The steps taken to reduce both infectious and noninfectious threats to the blood supply will be discussed. Donor adverse events resulting from both methods of collection will be detailed. Autologous and directed donation will be briefly discussed. The second half of the chapter details the methods of processing whole blood into components. Modifications, such as irradiation, leukocyte reduction, washing, and volume reduction will also be discussed. Understanding the process of obtaining, manufacturing, and transfusing blood is critical to interpreting clinical outcomes of blood administration.

Bacteremia

Donors who have undergone surgical and invasive dental procedures that are associated with transient bacteremia are deferred for 24 hours. Any increased body temperature will defer a donor for 24 hours. These measures are used to eliminate any donors that may have an acute illness. This is paired with postdonation information from donors who report any symptoms associated with infection, which will then trigger the quarantine of their product. Testing for bacterial contamination is performed only for platelets and discussed separately (see below).

Infectious disease testing

Infectious disease testing is performed using assays that are specifically licensed for blood donation and outlined in the Circular of Information prepared jointly by the AABB, the American Red Cross, America’s Blood Centers, and the Armed Services Blood Program, and recognized by the FDA. A list of all licensed tests for blood donors is available on the FDA portal within the blood product guidance. ( https://www.fda.gov/vaccines-blood-biologics/infectious-disease-tests ) The overall incidence of infectious disease transmission is low, and noninfectious complications from transfusion are collectively more frequent ( Table 91.1 ). Testing is performed using various classes of assays, including antibodies to pathogenic organisms, pathogen associated antigens (by enzyme immuno-assay, EIA), and/or nucleic acid testing (NAT) using either polymerase chain reaction (PCR) or transcription-mediated amplification (TMA) approaches. Positive results trigger retesting of the sample, and if repeatedly positive, it leads to disposal of the blood product and deferral of the blood donor. NAT was introduced in the late 1990s as a more sensitive method to detect specific viral nuclei acids, thereby decreasing the window period where serologic testing would be uninformative. This technology is more costly, and testing is typically performed in pooled samples of 6 to 16, with only a marginal reduction of sensitivity. Individual testing is performed if there is any positive result or if the prevalence of the viral agent is high (e.g., seasonal outbreaks of WNV). Donors are typically notified of any confirmed positive results by letter, except in the case for HIV, in which results are discussed in person. While most tests are false positives in a healthy donor population, the donor’s primary care physician typically performs further confirmatory testing.

Human immunodeficiency virus

HIV received the greatest global attention as it emerged in the early 1980s during a time when the collection process for donated blood was ill prepared to deal with an epidemic of a bloodborne virus. At the peak of the epidemic, 1 in 100 units of blood contained HIV in some cities in the United States. With current screening practices, this has fallen to a conservative over-estimation of 1 in 2 million blood units (see Table 91.1 ). HIV triggered practices that remain in place for screening of blood donors and the blood supply. Prevention of viral diseases cannot rely on laboratory testing (see below), especially given the window between infection and the ability to detect by laboratory testing. The FDA and AABB have mandated that all donors be given educational materials regarding HIV transmission, active infection, and risk behaviors, and asked to refrain from donating if at risk. Donors will also be informed that they will be tested for HIV and asked if that is why they are donating today (which in turn defers the donor), and will be informed as to where to obtain testing for HIV.

The DHQ has the most questions to identify and eliminate those at risk. Any donors that have had risk behaviors with anyone who: (1) has AIDS or a history of a positive HIV test, (2) has exchanged sex for money or drugs, (3) used non-prescription injection drugs, (4) men who have had sex with men (MSM), and (5) women who have had sex with MSM. Donors with these risks are now deferred for 3 months. This deferral period was recently adopted in the United States during the COVID-19 pandemic after consideration of the frequency of HIV positive blood donors and the past effect of decreasing deferrals to 1 year. If any potential donor has a history of a positive HIV test, they are permanently deferred. Antiretroviral therapy for the prevention of HIV (pre-exposure prophylaxis) or for post exposure prophylaxis has increased in frequency amongst otherwise healthy donors. Drug therapy for HIV may suppress viral loads to very low levels and may be undetectable while a donor is taking this medication. These donors are deferred for 3 months after their last dose of medication. Any donor that has tested positive for HIV in the past or is currently taking antiretroviral therapeutically is permanently deferred from blood donation even if viral testing yields negative results. Additional questions are asked about exposure to blood through needle-stick, tattoo, body fluid splash onto mucous membranes, recipients of tissue grafts or blood transfusion, and high-risk groups, including those who have been incarcerated for more than 72 hours (see Fig. 91.1 ).

There are multiple serologic tests available to detect anti-HIV-1 (groups M, N, and O) and anti-HIV-2 antibodies. If HIV-1 group O testing is not performed, donors must be evaluated for risk associated with HIV group O infection ( https://www.fda.gov/vaccines-blood-biologics/complete-list-donor-screening-assays-infectious-agents-and-hiv-diagnostic-assays ). Most commonly, a chemiluminescent immunoassay (ChLIA) is used to detect antibodies to HIV-1 and HIV-2. Donors who test antibody reactive are further evaluated to confirm the presence of HIV-1 or HIV-2 antibodies. Antibodies to HIV are detected at about 3 weeks after infection. NAT is performed for HIV-1 RNA to decrease the window between infection and detection to about 10 days. Donors testing falsely positive by either antibody or HIV NAT may be reentered, as outlined in FDA guidance ( http://www.fda.gov/downloads/BiologicsBloodVaccines/GuidanceComplianceRegulatoryInformation/Guidances/Blood/UCM210270.pdf ).

Human T-lymphotropic virus

HTLV-I and HTLV-II are retroviruses that have been associated with several disease states involving the nervous system, lymphadenopathy and lymphoma, and rarely leukemia. The current risk of transfusion-transmitted HTLV-I/II is less than 1 in 2 million (see Table 91.1 ). Screening has been performed only by laboratory testing in the United States since 1998.

Antibody detection for both HTLV-I and HTLV-II is performed using a combination test chemiluminescent EIA. There are no available NAT assays. Donors who test reactive for anti-HTLV-I/II are excluded as blood donors and there is no re-entry protocol.

Viral hepatitis

Much of the screening by history for viral hepatitis is based on the well-characterized transmission patterns of HBV and HCV. Recent changes to the universal DHQ have streamlined screening in the United States. Those who cared for, had sexual contact with, or lived with a person with viral hepatitis are deferred for 12 months since the last contact. As there is overlap in transmission patterns with HIV, questions for HIV exclusion also defer those patients who may also transmit viral hepatitis. All blood units are tested for Hepatitis B and C. Historically, serum alanine aminotransferase was used as a surrogate assay to detect viral hepatitis, but this was replaced with more specific testing in the early 1990s. The current estimate of transmitting HBV or HCV are about 1 in 2 million (see Table 91.1 ).

Several approaches are used to detect HBV infection, as no single assay reliably detects current or past infection. Hepatitis B surface antigen (HBsAg) testing was first introduced in 1972, with modern CLIAs setting the window between infection and detection at 35 to 40 days (for additional information on hepatitis testing and CLIA, refer to Chapters 51 and 26 , respectively). NAT testing to detect HBV DNA reduces this window period to about 3 to 4 weeks and is performed in pooled method of up to 16 samples. Assays for anti-HBV core antigen antibodies are also performed using an EIA and can be positive as early as 1 week after infection; however, there is a high false-positive rate, with up to 1% of donors testing positive. The test was nevertheless employed as there were rare patients who could potentially transmit HBV despite testing negative for HBsAG. Donors are deferred only if they are reactive on two separate occasions. Blood donor centers have different practices for counseling donors that are solely anti-HB core positive, with many donors delaying future donation by 3 to 6 months to avoid a second false positive result. For confirmation, HBsAg neutralization is used as a qualitative assay, though samples that are also HBV DNA reactive are immediately deemed positive. Anti-HB core reactive samples that are HBsAg and HBV DNA nonreactive are eligible for re-entry using a specialized NAT assay and may be reentered into the donor pool. ( http://www.fda.gov/downloads/BiologicsBloodVaccines/GuidanceComplianceRegulatoryInformation/Guidances/Blood/UCM210268.pdf ).

HCV detection strategies use a combination of methods to detect anti-viral antibodies and nucleic acids. A qualitative CLIA is used to detect anti-HCV antibodies that can take as long as 70 days after infection to appear. NAT for HCV RNA shortened this window to 8 to 10 days. Donors who are reactive for HCV-antibody reactive, but NAT negative by routine testing, are further tested using a different confirmatory HCV-antibody screening assay. Donors testing falsely positive by either antibody or HCV NAT may be reentered ( http://www.fda.gov/downloads/BiologicsBloodVaccines/GuidanceComplianceRegulatoryInformation/Guidances/Blood/UCM210270.pdf ).

Flavivirus

WNV and more recently Zika virus have emerged as important transfusion transmissible pathogens. Both are mosquito transmitted diseases which can cause a variety of symptoms ranging from none to fever, myalgia, arthralgia, and rash. WNV occurs seasonally in the United States, but patients are usually asymptomatic, and any symptoms are neither sensitive nor specific enough to identify donors by history, and thus only laboratory testing is performed to identify donors with active infection. WNV infection is usually self-limited, and viremia is thought to last less than 2 weeks. In fewer than 1% of cases, the infections lead to neuro-invasive disease including encephalitis. WNV can be transmitted through blood transfusion with case reports of fatality.

All blood products transfused in the United States are screened for WNV RNA, at minimum in a pooled method with up to 16 samples. Individual testing is triggered from the pooled approach when a local area detects a positive sample for WNV amongst the pooled samples. Individual testing is performed until no reactivity is detected for at least 7 days of testing. This strategy detects donors with low levels of viremia that can potentially transmit disease. Donors that test positive for WNV are temporarily deferred from donation for 120 days. There are no other confirmatory tests for WNV. The incidence of positive blood units during the peak of an outbreak is estimated at 1:25,000.

Zika virus (ZIKV) emerged in the past 5 years as a mosquito transmitted infection with the potential to be transmissible via transfusion. Symptoms of Zika include muscle or joint pain, headache, retro-orbital pain, conjunctivitis, skin rash, and fever. Most cases of Zika infection in adults are mild and self-limiting. ZIKV has been associated with congenital microcephaly and fetal loss in pregnant women. Cases of Guillain-Barré syndrome have also been reported with prior outbreaks of ZIKV infection in the South Pacific. There are two NAT based assays approved for detecting ZIKV RNA that are used in miniature pool testing strategies during periods of low prevalence ( https://www.fda.gov/regulatory-information/search-fda-guidance-documents/revised-recommendations-reducing-risk-zika-virus-transmission-blood-and-blood-components ). For additional information on NAT in microbiology, refer to Chapter 67 . An increase of cases would trigger the FDA to call for individual testing in a strategy that parallels WNV testing.

Cytomegalovirus

CMV infection is a herpesvirus that infects a significant percentage of people at a young age, with prevalence estimates ranging from 30% to 70%, varying widely by region. CMV infection is usually self-limited and mild, except in immunocompromised patients where infection can be severe and lead to fatality. Testing healthy donors for CMV would require several assays to detect those with the ability to transmit disease. Furthermore, transmission has been documented in cases where donors were seronegative for CMV. The main reservoir for CMV in blood is within the leukocyte fraction. Standard leukoreduction to fewer than 5 × 10 ⁶ leukocytes per red cell unit has been shown in trials to be equally as safe as serologically tested units. For this reason, most physicians consider leukoreduced blood units to be CMV-safe.

Malaria

Transfusion-transmitted malaria, though common in some parts of the world, is extremely rare in the United States, with a frequency of fewer than 1 in 2 million units. There have been long term policies to exclude donors at risk for transmitting malaria, as no laboratory testing is performed on donated blood. Malarial infection and carrier states are varying with regard to symptoms, with asymptomatic patients harboring parasites for years. For this reason, those with a diagnostic history of malaria, or residents of countries endemic are deferred for 3 years. Travelers to endemic areas are deferred for 3 months from return. The FDA is now considering pathogen reduction as a means to include donors that would be deferred, as there is evidence that malaria transmission may be mitigated by such means.

Chagas disease

Chagas infection with the parasite T. cruzi is endemic in Latin America and reported to be potentially transfusion-transmitted in North America in fewer than 10 cases. Blood donors in the United States are no longer asked if they have ever had Chagas and deferred based on their history. Donors are screened once by laboratory testing and are permanently deferred if positive, with no re-entry available. Testing for Chagas is done by a CLIA to detect antibodies to the parasite, with a second supplemental test available. An enzyme strip immunoassay using recombinant antigen is used for confirmatory testing.