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Blood Bank

Instrumentation

The modern Blood Bank relies on a combination of basic mechanical devices and sophisticated robotics to ensure the accuracy of serological testing and the safety of blood products. While automation handles the bulk of high-volume screening, manual instrumentation remains the “Gold Standard” for problem-solving and emergency testing

Microscope

The bright-field microscope is the final arbiter for distinguishing between true agglutination and false-positive interferences. It is used primarily when macroscopic (visual) readings are inconclusive or to differentiate Rouleaux from agglutination

  • Optics: A 10x Objective is standard (100x total magnification). The aperture diaphragm (iris) should be partially closed to reduce light intensity and increase contrast, making the translucent red cells visible
  • Applications
    • Confirming negative AHG reactions
    • Rouleaux: Red cells stack like coins due to protein; disperses with saline replacement
    • Agglutination: Irregular, grape-like clusters; does not disperse
    • Mixed Field: Distinct clumps sitting in a sea of free cells (e.g., O cells in an A patient)

Centrifuge

The centrifuge uses centrifugal force (RCF) to bring antigens and antibodies together or to separate blood components. It is the workhorse of the manual bench

  • Calibration: Speed (RPM) and Time must be calibrated to achieve the “Optimal Spin” - the shortest time required to produce a clearly defined cell button that resuspends easily
    • Under-centrifugation: Causes False Negatives (cells not close enough to bind)
    • Over-centrifugation: Causes False Positives (button packed too tight) or False Negatives (vigorous shaking breaks the reaction)
  • Component Centrifuges: Large, refrigerated floor units used to separate plasma from red cells. They must maintain strict temperature controls (\(4^\circ\text{C}\) or \(20^\circ\text{C}\)) to preserve product viability

Cell Washer

An automated version of the serological centrifuge designed specifically for the Antiglobulin Test (Coombs Test). Its purpose is to standardize the washing phase to remove unbound globulins

  • Function: Automatically adds saline, spins, and decants supernatant 3-4 times
  • Criticality: Inadequate washing leads to Neutralization of the AHG reagent by residual plasma proteins, resulting in a False Negative IAT
  • QC: Daily testing with Check Cells is mandatory. If Check Cells fail (negative), the washer is often the culprit (clogged lines or poor decanting)

Irradiator

A specialized device used to modify cellular blood products (RBCs and Platelets) to prevent Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD) in immunocompromised patients

  • Principle: Uses Gamma rays (Cesium-137) or X-rays to damage the DNA of donor T-Lymphocytes, preventing them from replicating and attacking the host. Red cells and platelets are spared as they do not replicate
  • Dosage: The center of the bag must receive 25 Gy; no part may receive < 15 Gy
  • Indicators: A radiation-sensitive tag (Rad-Tag) must be affixed to every unit to visually verify exposure (e.g., turns from pink to black)
  • Expiration: Irradiation damages the RBC membrane (potassium leak). The shelf life of RBCs is reduced to 28 days (or original date, whichever is sooner) immediately upon treatment

Automated Analyzers

Robotic platforms (e.g., Ortho Vision, Immucor Echo) that perform ABO/Rh, Antibody Screens, and Crossmatches. They offer standardization, traceability, and high throughput

  • Column Agglutination (Gel): The reaction occurs in a micro-tube filled with gel
    • Positive: Agglutinated cells are trapped at the top of the gel
    • Negative: Cells pass through the gel to the bottom
  • Solid Phase Adherence: Antigens are coated on the bottom of a micro-well
    • Positive: Cells adhere to the wall/bottom as a diffuse carpet
    • Negative: Cells slide down to form a tight button
  • Advantages: Eliminates subjective interpretation, archives images of reactions, and prevents transcription errors via barcode scanning. However, they are highly sensitive and may detect clinically insignificant antibodies that manual tube testing misses