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Blood Bank

Automated Analyzers

The transition from manual tube testing to automated platforms represents the most significant operational shift in the modern Blood Bank. Automated analyzers are designed to perform ABO/Rh typing, Antibody Screening, and even Crossmatching with higher throughput, greater standardization, and improved traceability compared to manual methods. While manual testing remains the “Gold Standard” for problem-solving, automation is the standard of care for routine screening in medium-to-large facilities

Methodologies

Automated blood bank analyzers generally utilize one of three distinct technologies to detect antigen-antibody reactions. Unlike the tube method, these technologies do not rely on creating a cell button that is shaken loose; rather, they rely on the distribution of cells within a matrix

Column Agglutination Technology (CAT) - “The Gel Card”

This is the most widely adopted technology (e.g., Ortho Vision, Grifols Erytra)

  • Principle: The reaction takes place in a micro-column (a small tube within a card) containing a dextran-acrylamide gel matrix
  • Process
    1. Reagents and patient sample are pipetted into the reaction chamber at the top of the column
    2. The card is incubated (if required) and then centrifuged
    3. The Gel acts as a sieve.
  • Interpretation
    • Positive (Agglutination): Agglutinated cells are too large to pass through the gel matrix. They get trapped at the top of the column or suspended within it
      • 4+ Reaction: Solid band of cells at the very top
    • Negative: Un-agglutinated cells are small enough to pass through the pores of the gel. During centrifugation, they pellet at the bottom of the column
  • Advantages: Stable endpoint (results can be reviewed hours later), highly sensitive, and standardized reading (no shaking variability)

Solid Phase Red Cell Adherence (SPRCA) - “The Microplate”

Used primarily by systems like Immucor Echo/Neo

  • Principle: The “target” antigen is affixed to the bottom of a microplate well
  • Process
    1. Antigen: For antibody screens, the Reagent Red Cell membranes are dried/bound to the bottom of the well
    2. Add Patient: Patient serum is added. If antibodies are present, they bind to the antigens on the plastic wall
    3. Wash: Unbound proteins are washed away
    4. Indicator: IgG-coated Indicator Red Cells are added
    5. Centrifugation
  • Interpretation
    • Positive (Adherence): The Indicator Cells bind to the patient’s antibody (which is bound to the well wall). The result is a diffuse carpet or monolayer of cells across the bottom of the well
    • Negative: No patient antibody is on the wall. The Indicator Cells have nothing to grab onto. During centrifugation, they slide down the sides and form a tight, compact button at the bottom
    • Mnemonic: “Solid Positive, Button Negative.” (Note: This is visually opposite to Hemagglutination Inhibition testing)

Erythrocyte Magnetized Technology (EMT)

Used by the Bio-Rad IH-1000/500 (in some markets)

  • Principle: Utilizes magnetic beads to eliminate the washing and centrifugation steps
  • Process: Reagent Red Cells are magnetized. When placed in a magnetic field, they are pulled to the bottom of the well during washing, preventing loss without spinning

Operational Components

Automated analyzers are essentially robotic pipettors combined with incubators, centrifuges, and cameras

  • Sample Handling
    • Barcoding: The absolute reliance on barcode scanning (Sample ID) prevents transcription errors, a major source of preanalytical error
    • Clot Detection: Pressure sensors in the probe detect clots or fibrin strands during aspiration, preventing “short samples” or erroneous results
    • Liquid Level Sensing: Ensures sufficient sample volume exists before starting the test
  • Reagent Management
    • On-board refrigeration keeps reagents stable
    • Reagent lot tracking prevents the use of expired products
  • Image Analysis
    • A high-resolution camera takes a picture of the final reaction (Gel card or Microplate well)
    • Software algorithms interpret the pixel density to grade the reaction (0 to 4+)
    • The “Grey Zone”: If the computer is unsure (e.g., a dusty background or ambiguous cell button), it flags the result for manual review by a laboratory scientist

Advantages Over Manual Testing

  1. Objectivity: Removes the “subjective eye” of the laboratory scientist. A 1+ reaction is graded consistently by the software, whereas two techs might call it weak positive vs. negative
  2. Traceability: Every step is logged. Who ran it? What reagent lot? What time? The camera image is archived permanently for audit
  3. Safety: Cap-piercing capabilities reduce the risk of exposure to bloodborne pathogens
  4. Sensitivity: Both Gel and Solid Phase are generally more sensitive than manual Tube testing for detecting antibodies. (Note: This can be a double-edged sword, as they detect more “junk” or insignificant antibodies like warm autoantibodies)

Limitations & Troubleshooting

Automation is not infallible. The laboratory scientist must recognize when to revert to manual methods

  • Sample Integrity Issues
    • Lipemia: Can cause interference in light transmission (Gel) or coating (Solid Phase)
    • Hemolysis: The analyzer generally cannot distinguish between in vivo hemolysis and hemolysis caused by the probe
    • Fibrin: The arch-enemy of automation. Fibrin bits can mimic agglutination in Gel cards (trapped on top)
  • “QNS” (Quantity Not Sufficient): Analyzers have significant “dead volume” requirements. Pediatric samples often must be tested manually
  • Limitations of Detection
    • IgM vs IgG: Most automated antibody screens are strictly IgG (Anti-IgG AHG). They may miss IgM antibodies (like Anti-M or Anti-P1) that would be seen in an Immediate Spin tube test. This is generally considered a feature, not a bug, as these are clinically insignificant, but it explains discrepancies between methods
    • Rouleaux: While Gel is resistant to Rouleaux (the centrifugation separates the stacked cells), Solid Phase can sometimes show interference

Quality Control for Automation

QC is run daily, just like manual testing, but with stricter software controls

  • Positive/Negative Controls: Must be run for every reagent rack loaded
  • Software Validation: Whenever the instrument software is updated, a validation study must be performed to ensure it still interprets images correctly
  • Maintenance
    • Probe Cleaning: Essential to prevent carryover (contamination of one sample with another)
    • Camera Cleaning: Dust on the lens looks like a cell button to the computer