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Blood Bank

Preanalytical, Analytical, Postanalytical

In Blood Bank, Quality Assessment (QA) is not merely a regulatory requirement; it is the primary firewall against fatal transfusion reactions. Unlike other areas of the clinical laboratory where an error might result in a misdiagnosis, an error in Blood Bank - specifically regarding ABO compatibility - can lead to immediate patient death. Therefore, Laboratory Operations are governed by a Quality Management System (QMS) that strictly adheres to standards set by the AABB (formerly American Association of Blood Banks), the FDA (Code of Federal Regulations), and the College of American Pathologists (CAP). The workflow is divided into the Total Process of Workflow: Preanalytical, Analytical, and Postanalytical phases

Preanalytical

The preanalytical phase encompasses all processes occurring before the actual testing of the specimen begins. In Immunohematology, this is the most critical phase, as the majority of fatal acute hemolytic transfusion reactions are caused by clerical errors regarding patient identification and specimen labeling at this stage

Patient Identification & Specimen Collection

Strict adherence to identification protocols is the cornerstone of preanalytical QA. If a sample is mislabeled, the most accurate analytical testing in the world will only serve to confirm the blood type of the wrong person

  • Two Unique Identifiers: All specimens must be labeled with at least two unique identifiers (e.g., full patient name and medical record number/date of birth) at the bedside
  • The Phlebotomist’s Signature: The individual collecting the sample must identify themselves on the tube label and requisition, certifying that they verified the patient’s ID band against the request
  • The “Blood Bank Armband”: Many facilities utilize a secondary identification system, such as a typenex band or barcode system, specifically for blood bank specimens to ensure the physical link between the patient and the specimen is never broken
  • Sample Age (The 3-Day Rule): To ensure the patient’s current immunological status is represented, a sample must be drawn within 3 days of the scheduled transfusion if the patient has been pregnant or transfused within the last 3 months (or if history is unknown). This ensures that any newly developing antibodies are detected

Specimen Integrity & Rejection Criteria

Upon receipt in the laboratory, the laboratory scientist must evaluate the specimen for suitability. Processing an unsuitable specimen compromises the validity of the results

  • Hemolysis: Hemolyzed samples are generally rejected because mechanical or chemical hemolysis in the tube can mask in vitro hemolysis, which is a positive result in complement-dependent antigen-antibody reactions
  • Lipemia: Excessive lipids can interfere with agglutination interpretation or automated testing systems
  • Wrong Blood in Tube (WBIT): If a discrepancy is found between the current sample and historical records (e.g., patient was Group O historically but tests as Group A today), the preanalytical assumption must be a collection error. The sample must be redrawn
  • Requisition Matching: Any discrepancy between the tube label and the electronic or paper requisition constitutes grounds for rejection. Blood Bank specimens are rarely, if ever, candidates for “correction” forms due to the high risk

Donor Preanalytical Processing

For donor centers, the preanalytical phase involves the protection of both the donor and the recipient

  • Donor History Questionnaire (DHQ): A standardized interview to identify high-risk behaviors or medical conditions (e.g., travel to malarial zones, history of hepatitis)
  • Physical Exam: Vital signs (temperature, pulse, blood pressure) and hemoglobin/hematocrit levels (minimum 12.5 g/dL or 38% for allogeneic donation) are checked to ensure the donor can safely tolerate the volume loss

Analytical

The analytical phase covers the actual performance of laboratory testing. This includes the validation of reagents, the calibration of equipment, and the technical competence of the testing personnel. The goal is to ensure accuracy (closeness to the true value) and precision (reproducibility)

Reagent Quality Control

Commercially prepared reagents (Anti-A, Anti-B, Anti-D, Reagent Red Cells, and Anti-Human Globulin) must be tested to prove they are reacting as expected

  • Daily QC: Reagents must be tested every day of use to verify reactivity. This involves testing antisera against known antigen-positive cells (to prove potency) and antigen-negative cells (to prove specificity)
  • Visual Inspection: Reagents must be inspected for turbidity, precipitate, or discoloration, which may indicate bacterial contamination
  • Anti-Human Globulin (AHG): This is the most critical reagent in antibody detection. QA requires the use of IgG-sensitized red cells (Coombs Control or “Check Cells”) to validate all negative AHG reactions. If check cells do not agglutinate, the test is invalid (false negative) and must be repeated

Equipment Maintenance & Calibration

Equipment function is directly tied to the ability to visualize agglutination or preserve blood products

  • Serological Centrifuges: Must be calibrated for speed (RPM) and time. The “optimal spin” is determined to produce a distinct cell button that resuspends easily without being too loose (false negative) or too tight (false positive)
  • Temperature Controlled Chambers
    • Water baths/Heat blocks: Must maintain \(37^\circ\text{C}\) to simulate body temperature for clinically significant IgG antibodies
    • Refrigerators: Must maintain \(1^\circ\text{C}\) to \(6^\circ\text{C}\) for red cell storage
    • Freezers: Plasma freezers must maintain \(\le -18^\circ\text{C}\)
    • Alarm Systems: Continuous monitoring charts and audible alarms must be tested periodically (e.g., quarterly) to ensure they activate before storage units reach unacceptable temperatures

Troubleshooting Analytical Errors

When Quality Control fails or results are discrepant, the laboratory scientist must troubleshoot

  • False Negatives (The result looks negative, but antibody/antigen is present)
    • Failure to add AHG reagent
    • Inadequate washing of cells (unbound globulins neutralize AHG)
    • Heavy cell suspension (antigen excess/post-zone)
    • Under-centrifugation
  • False Positives (The result looks positive, but is not due to specific antigen-antibody binding)
    • Over-centrifugation (tight button)
    • Dirty glassware or contaminated saline
    • Rouleaux formation (coin-stacking of RBCs due to high protein, resolved by saline replacement)
    • Fibrin interference (clots mimicking agglutination)

Proficiency Testing (PT) & Competency

To verify analytical accuracy, laboratories participate in external Proficiency Testing (e.g., CAP surveys). Unknown samples are tested as if they were patient samples, and results are graded against peer laboratories. Furthermore, personnel competency is assessed semiannually (for new hires) and annually using direct observation, written testing, and problem-solving scenarios

Postanalytical

The postanalytical phase focuses on the output of the data, the interpretation of results, and the issuance of blood products. This phase ensures that the accurate result obtained in the analytical phase is translated into safe clinical action

Data Management & Reporting

Modern Blood Banks rely heavily on Laboratory Information Systems (LIS) to prevent errors

  • Computer Logic/Truth Tables: The LIS should be programmed to flag incompatibilities. For example, if a patient is typed as Group O, the system must prevent the crossmatching of Group A red cells
  • Delta Checks: The system compares current results with historical records. A discrepancy (e.g., a patient with a history of Anti-K now screening negative) requires a manual review to ensure the historical antibody is honored (an “electronic” antigen-negative requirement)
  • Transcription Verification: If manual entry is used, a secondary check is often required to prevent keyboard entry errors

Product Issuance & Inspection

The final “gate” before a product reaches a patient is the issuance desk

  • Visual Inspection of Components: Before release, every unit must be inspected for:
    • Abnormal color (purple/black may indicate bacterial contamination)
    • Clots
    • Leakage or port integrity
    • Hemolysis in the bag segments
  • Final Identity Check: The unit tag (compatibility label) must be cross-referenced with the unit label and the patient requisition. This includes ABO/Rh, Unit ID, Expiration, and Patient Identifiers

Post-Transfusion Review & Reaction Workup

QA extends to monitoring the patient after the blood leaves the lab

  • Transfusion Reaction Workup: If a reaction is suspected, the lab performs a clerical check, a visual check for hemolysis in post-transfusion samples, and a Direct Antiglobulin Test (DAT)
  • Look-Back Processes: If a donor is found to test positive for an infectious disease (e.g., HIV, HCV) after previous donations, Blood Bank must identify and notify all recipients of units from that donor’s previous donations (quarantine and retrieval)

Documentation & Record Retention

Regulatory bodies mandate specific retention times for records to allow for traceability

  • Indefinite Retention: Records of patients with difficulty typing, severe reactions, or unexpected antibodies
  • Minimum 10 Years (often varies by state/agency): Traceability of units from donor to recipient and vice versa
  • 5 Years: Most QC and maintenance records

Troubleshooting Process Improvement

When an error is detected in any of these three phases, the Quality Assessment plan dictates the response mechanism

  • Root Cause Analysis (RCA): A systematic process to identify the fundamental reason for the variance (e.g., “Why did the laboratory scientist mislabel the tube?” leading to “Because the staffing was short and the printer was broken”)
  • Corrective Action (CA): Immediate fix (e.g., Retraining the employee)
  • Preventative Action (PA): Long-term system fix (e.g., Implementing barcode scanning to prevent future mislabeling)