Standard Operating Procedure: ABO Grouping (Tube Method)

1. Purpose

To provide a standardized procedure for the determination of ABO blood groups using the tube agglutination method, ensuring accuracy and patient safety in transfusion medicine.

2. Principle

ABO grouping involves two parts: Forward Grouping (detecting antigens on patient red cells) and Reverse Grouping (detecting antibodies in patient serum/plasma). The test relies on hemagglutination, where specific antibodies (anti-A, anti-B) react with corresponding antigens on the red blood cells, causing visible clumping.

3. Materials and Reagents

• Test tubes (10x75 mm or 12x75 mm)
• Centrifuge (serological)
• Monoclonal Anti-A, Anti-B, and Anti-A,B reagents
• Known A1 and B reagent red cells
• Patient specimen (EDTA or clotted blood)
• Normal Saline (0.9% NaCl)
• Optical aid (light box/microscope)

4. Procedure

Forward Grouping (Cell Typing)

1. Prepare a 2-5% suspension of patient red cells in normal saline.
2. Label three tubes: A, B, and AB (for control/Anti-A,B).
3. Add one drop of the appropriate reagent (Anti-A in tube 1, Anti-B in tube 2, Anti-A,B in tube 3).
4. Add one drop of the 2-5% patient red cell suspension to each tube.
5. Centrifuge at 3400 rpm for 15 seconds or as per manufacturer instructions.
6. Gently resuspend the cell button and observe for agglutination.

Reverse Grouping (Serum Typing)

1. Label two tubes: A1 and B.
2. Add two drops of patient serum/plasma to each tube.
3. Add one drop of reagent A1 cells to the A1 tube and reagent B cells to the B tube.
4. Centrifuge at 3400 rpm for 15 seconds.
5. Gently resuspend and observe for agglutination.

5. Interpretation of Results

6. Quality Control

Perform daily checks using known positive and negative controls for all reagents. Ensure reagents are within expiry dates and stored at the recommended temperature (2-8C). If results are inconsistent, repeat the testing with fresh reagents and confirm the patient's identification.

7. Troubleshooting

If forward and reverse grouping results show a discrepancy:

• Re-verify patient identification.
• Check for technical errors (e.g., reagent misidentification, over-centrifugation).
• Consider patient history (e.g., recent transfusion, bone marrow transplant, or immunosuppression).
• Perform an auto-control to rule out auto-antibodies.