Quality Control

In the context of the Clinical Blood Bank, Quality Control (QC) refers to the routine analytical procedures utilized to monitor the components of the testing process. While Quality Assessment (QA) looks at the entire workflow, QC is specifically focused on the immediate validation of test reliability. The primary goal of QC is to ensure that reagents are potent and specific, equipment is functioning within calibrated parameters, and the final blood components meet regulatory standards for safety and efficacy. Failure of QC constitutes an immediate “stop-work” condition; patient results cannot be reported until the QC failure is resolved and documented

Reagent QC

Blood bank reagents are biological products derived from human or monoclonal sources. Because they can degrade over time due to improper storage or contamination, they must be tested each day of use to verify their reactivity. The two main concepts verified during reagent QC are Potency (the ability to detect the antigen/antibody when present) and Specificity (the ability to yield a negative result when the antigen/antibody is absent)

Antisera & Reagent Red Blood Cells

Routine reagents such as Anti-A, Anti-B, Anti-D, and Reverse Grouping Cells must undergo daily validation

• Visual Inspection: Before use, all vials must be inspected for cloudiness, turbidity, or particulate matter, which may indicate bacterial contamination. Discolored reagents must be discarded
• Testing for Potency (Sensitivity): Reagents must react with “weak” antigen-positive cells. For example, Anti-A is tested against A-positive cells. If agglutination occurs, the reagent has sufficient potency
• Testing for Specificity: Reagents must be tested against antigen-negative cells. For example, Anti-A is tested against B cells. The result must be negative. If agglutination occurs, the reagent lacks specificity (possibly due to contamination or spontaneous agglutination)
• Anti-D QC: This is unique because Anti-D reagents often contain high protein or potentiators. A “Rh Control” (or use of an autocontrol) is often required to ensure that a positive reaction is due to the D-antigen and not the media causing agglutination

Antiglobulin Reagent (AHG) QC

Anti-Human Globulin (AHG) is the most critical reagent in the detection of unexpected antibodies (IAT) and in vivo hemolysis (DAT). Because AHG creates a “bridge” between antibodies attached to red cells, its failure leads to false-negative results, which can cause fatal transfusion reactions

• Daily Testing: AHG must be tested daily with IgG-sensitized cells to prove reactivity
• Coombs Control (Check Cells): This is a mandatory component of AHG testing. If an antibody screen or crossmatch is negative at the AHG phase, Check Cells (IgG-sensitized RBCs) must be added
  • Expected Result: Agglutination. This proves that the AHG reagent was added, it was active (not neutralized), and the cell washing step was adequate
  • QC Failure: If Check Cells do not agglutinate, the entire test is invalid and must be repeated. The most common cause is inadequate washing, where free plasma globulins neutralize the AHG reagent

Equipment QC

The physical devices used in the laboratory are subject to wear and mechanical drift. QC programs for equipment ensure that the physical conditions (speed, temperature, time) required for antigen-antibody binding are consistently met

Serological Centrifuges

Centrifugation is the method used to bring antigens and antibodies together. If the force is too low, false negatives occur; if too high, false positives (button difficult to dislodge) occur

• Speed (RPM): Checked quarterly using a tachometer (strobe light or contact) to ensure the centrifuge spins at the manufacturer’s specified speed
• Timer: Checked quarterly using a NIST-calibrated stopwatch
• Function Check (Optimal Spin): This is the most practical QC measure. It determines the shortest time required to produce a clearly delineated cell button that is easily resuspended. This is critical for reading weak (1+) reactions
• Cleaning: Routine cleaning to prevent imbalance or biohazard accumulation is required

Temperature-Dependent Equipment

Immunological reactions are temperature dependent (e.g., ABO is IgM and reacts at room temperature; clinically significant antibodies are IgG and react at \(37^\circ\text{C}\))

• Water Baths and Heat Blocks: Must be maintained at \(37^\circ\text{C} \pm 1^\circ\text{C}\). Temperature is recorded daily using a calibrated thermometer
• Refrigerators: Blood storage refrigerators must be maintained between \(1^\circ\text{C}\) and \(6^\circ\text{C}\)
  • QC includes checking the temperature recording charts (continuous monitoring)
  • Alarm Checks: Alarms must be tested periodically (often quarterly) to ensure they activate before the unit goes out of range (e.g., alarm should sound at \(1.5^\circ\text{C}\) and \(5.5^\circ\text{C}\))
• Freezers: Plasma freezers must be \(\le -18^\circ\text{C}\). Alarms must also be verified
• Thermometers: All thermometers used for QC must be calibrated periodically against a NIST-certified standard thermometer to ensure accuracy

Cell Washers

Automated cell washers used for the AHG test must be checked for saline delivery volume and decanting efficiency

• Residual Saline: If the washer leaves too much saline, the AHG is diluted
• Incomplete Decant: If the washer does not remove all the saline/supernatant, “Check Cells” may fail due to neutralization by residual plasma proteins

Blood Component QC

Beyond testing patient samples, Blood Bank must perform QC on the blood products themselves to ensure they meet FDA and AABB requirements for therapeutic efficacy. Since it is destructive to test every unit, a statistical sampling (e.g., 1% of production or 4 units per month) is usually performed

Platelet Components

Platelets are highly susceptible to storage lesions (pH drop) and bacterial growth due to room temperature storage

• pH: Must be \(\ge 6.2\) at the end of the allowable storage period
• Platelet Count (Whole Blood Derived): Must contain \(> 5.5 \times 10^{10}\) platelets per unit in at least 90% of units tested
• Platelet Count (Apheresis): Must contain \(> 3.0 \times 10^{11}\) platelets per unit in at least 90% of units tested
• Bacterial Detection: All platelet units must be screened for bacterial contamination using approved culture methods or rapid detection devices prior to issue

Cryoprecipitate & Red Blood Cells

• Cryoprecipitate AHF: Used for Fibrinogen replacement. QC must demonstrate that units contain \(\ge 150\) mg of Fibrinogen and \(\ge 80\) IU of Factor VIII per unit
• Leukoreduced RBCs: QC must verify that the filtration process was successful. The unit must retain \(\ge 85\%\) of the original red cells and contain \(< 5.0 \times 10^6\) residual white blood cells (to prevent febrile reactions and HLA alloimmunization)

Irradiators

Irradiation prevents Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD). QC ensures the correct dose (25 Gy to the center of the canister) is delivered

• Dosimetry: Annual mapping of the radiation field
• Batch QC: Each unit irradiated must carry a radiation-sensitive tag (indicator label) that changes color (e.g., from pink to black) to visually verify that the unit was exposed to the source

Troubleshooting QC Failures

When Quality Control results fall outside acceptable limits, the laboratory scientist must follow a logical troubleshooting path. No patient results can be released until the QC is corrected

• Repeat the Test: The first step is to rule out random error (clerical, pipetting, or contamination). Repeat the QC using the same reagents
• Switch Reagents: If the repeat fails, open a new vial of reagent (different lot number if possible). Reagents may have lost potency due to being left out on the counter (thermal degradation)
• Check Equipment: If multiple reagents fail, check the equipment. Is the centrifuge spinning fast enough? Is the incubator actually at \(37^\circ\text{C}\)?
• Corrective Action Documentation: All QC failures must be documented. The log must state:
  • The out-of-range result
  • The action taken (e.g., “Reagent discarded, new vial opened”)
  • The final acceptable result
  • The signature/date of the laboratory scientist