Blood Component & Testing - Part 3

Blood Components and Testing

Introduction to Blood Testing

  • Focus on the testing conducted in blood banks to ensure the safety of blood products prior to transfusion.

  • Emphasis on the necessity of tests at each donation, treating every donation as if it were the first.

  • Assurance of safety in receiving blood components in the United States due to rigorous testing.

Evolution of Pathogens and Testing Methods

  • Recognition that bacterial, viral, parasitic, and prion pathogens are constantly evolving, necessitating ongoing development of new tests.

  • Importance of testing to identify pathogens that could harm patients or lead to fatalities.

  • Acknowledgment that not all pathogens are tested for directly but can be identified through donor questionnaires.

Component Testing

  • Initial testing performed on blood component bags includes blood typing:

    • Forward Type: Identifies the antigens present on the red blood cells.

    • Reverse Type: Confirms which antibodies are present in the serum.

  • Rh Typing: Conducted to label units correctly, especially for Rh negative donors.

    • Weak D typing is mandatory for Rh negative donors; if positive, unit is labeled Rh positive to prevent transfusion errors.

Antibody Screening

  • Screening for clinically significant alloantibodies:

    • If an alloantibody is identified, the plasma and platelets are discarded, as these contain antibodies.

    • Packed red blood cells are labeled with the identified antibody; some facilities may wash the unit for extra safety.

Infectious Disease Testing

  • **Hepatitis Testing:

    • Hepatitis surface antigen (HBsAg) testing can be conducted using instruments or nucleic acid testing.

    • Reaction protocol: If initial tests are positive:

    • Repeat tests in duplicate; 2 out of 3 positives indicate possible infection.

    • Neutralization test must confirm infection; if confirmation is negative, unit is destroyed, donor deferred for 8 weeks.

  • Hepatitis B Core:

    • Presence indicates possible hepatitis B infection; if detected alongside HBsAg, the donor is permanently deferred.

  • Hepatitis C Testing:

    • Anti-hepatitis C antibodies detection and nucleic acid tests (NAT) for HCV RNA.

    • Confirmation testing includes RIBA (recombinant immunoblot assay).

  • Hepatitis A:

    • Transmitted via the fecal-oral route; testing is done contingent on outbreaks.

  • Overall Importance:

    • Significant reduction in hepatitis C transmission due to testing since 1992.

Testing for HIV and Other Infectious Agents

  • HIV Testing:

    • Screening for antibodies (types 1 and 2) and nucleic acid testing; confirmation testing has replaced Western blot with newer methods.

  • HTLV Testing:

    • Human T-cell lymphotropic virus testing, associated with T-cell leukemia; prevalent among IV drug users.

  • West Nile Virus:

    • Testing initiated in 1999; units with reactive results destroyed. 120-day deferral for donors with previous infections during outbreak periods.

  • Syphilis Testing:

    • Testing performed via RPR (Rapid Plasma Reagin) test, discarded upon positive results and confirmed with fluorescent treponemal antibody tests.

  • Chagas Disease:

    • Caused by Trypanosoma cruzi and endemic to certain regions; indefinite deferral for positive tests due to lack of confirmatory test.

  • Zika Virus Testing:

    • Recommended screening due to undetected symptoms, primarily focused on nucleic acid tests.

Pathogen Reduction Technology

  • Discussed as an emerging field,

    • Limited current applications to platelets and plasma; documentation of Zika virus transfusion cases primarily in regions outside the U.S.

Prion Disease and Other Considerations

  • Creutzfeldt-Jakob Disease:

    • A rare disease linked to contaminated tissues and possible history-related inquiries on the donor questionnaires; deferrals apply for relevant family history.

  • Bacterial Detection in Platelets:

    • Monitoring platelet units for contamination due to storage conditions poses risks.

    • Tests differentiate between gram-negative and gram-positive organisms; procedures involve culturing and identification.

Reactive Results Procedures

  • Reactivity protocols following positive tests involve a "look back" process:

    • Identify and trace previous donations of reactive donors to prevent further infections.

    • Actions vary by type of infectious agent; protocols help prevent transmitting infections from undetected periods to recipients.

Conclusion

  • Overall, rigorous testing and careful donor selection, along with innovative testing methods, aim to ensure the utmost safety and reduce risks associated with blood transfusions.