Blood Group Testing
Introduction
A blood group test is a medical test used to determine the blood group of an individual. There are four main blood groups: A, B, AB, and O. Each of these blood groups is determined by the presence or absence of certain proteins, called antigens, on the surface of red blood cells.
The blood group test involves taking a small sample of blood from the individual and then testing it in a laboratory to determine the blood group. This test is important for various medical procedures such as blood transfusions, organ transplants, and prenatal testing.
Blood transfusions must be carefully matched with the recipient’s blood type to avoid a potentially life-threatening reaction. If incompatible blood is given during a transfusion, the recipient’s immune system may attack the transfused blood cells, leading to a condition known as hemolytic reaction. Therefore, the blood group test is an essential part of the pre-transfusion process.
In addition to the ABO blood group system, there is also another blood group system called the Rh system, which is based on the presence or absence of another antigen called the Rh factor. Blood group testing typically includes testing for both ABO and Rh antigens.
It is important to note that blood group testing is a routine procedure and does not indicate any disease or health condition in itself.
Blood group test methods
There are several methods for blood group testing, but the most common ones are:
- Blood Typing: This method is based on the reaction of the individual’s blood with specific antibodies. Antibodies are proteins that recognize and bind to specific antigens. For example, if a sample of blood reacts with anti-A antibodies, it means that the blood contains the A antigen.
- Slide Agglutination Test: In this method, a drop of blood is mixed with a drop of saline solution containing specific antibodies. The mixture is then observed under a microscope for agglutination (clumping) of red blood cells. If the red blood cells clump together, it indicates that the blood contains the corresponding antigen.
- Gel Test: This is a newer method that uses a gel matrix to separate the blood cells from the plasma. Specific antibodies are added to the gel matrix, and if the blood contains the corresponding antigen, the red blood cells will migrate towards the antibody, forming a visible line.
- Automated Blood Grouping: This method uses specialized equipment to automate the blood typing process. The equipment analyzes the reaction of the blood sample with specific antibodies and produces a result automatically.
Qualitative Test For Blood Group Testing
Principle
The procedures used with the antisera are based on the principle of agglutination. Normal human red cells possessing antigens, will clump in the presence of corresponding antibody.
Method
Slide Agglutination Method
Requirements
- Glass slides
- Pasteur pipettes
- Applicator stick
- Centrifuge
Reagents
- Anti -A sera (blue color) : Human polyclonol or murine monoclonal.
- Anti -B sera (Yellow color) : Human polyclonol or murine monoclonal.
- Anti -AB sera (Pink color) : Human polyclonol or murine monoclonal.
- Normal saline (0.85g/dl sodium chloride in distilled water).
Specimen collection and Preparation
No special preparation of the patient is required prior to specimen collection. Blood should be collected by approved technique. That test should be performed immediately, otherwise it is necessary to store the specimen at 2-8 degrees Celsius.
| Red cells collected | Should be tested within |
| EDTA | 2 days |
| Oxalate | 14 days |
| Heparin | 2 days |
| Sodium citrate | 14 days |
| ACD (acid citrate dextrose) | 28 days |
| Clotted whole blood | 14 days |
Procedure
- Prepare a 10% suspension of red blood cells in normal saline (preparation method as given below).
- Mix 5 Drops (0.05 ml each) of sedimented red cells with 2 ml of normal saline.
- Centrifuge at 1500 RPM for 1 to 2 minutes. Discard supernatant.
- Add 2 ml of normal saline to the sedimented red cells. Mix well. This gives a 10% suspension of red cells.
- On one half of a glass slide slide, place one drop of Anti-A. blood grouping serum.
- On the other half of the slide place one drop of Anti-B blood grouping serum.
- On the other half of the slide place one drop of Anti-AB blood grouping serum.
- Using a Pasteur pipette add 1 drop of the cell suspension to each half of the slide.
- With separate applicator sticks, mix each cell serum mixture well.
- Tilt the slide back and forth and observe for agglutination.
- Test that show no agglutination within two minutes are considered negative.
- Do not interpret peripheral drying or fibrin strands as agglutination.
Interpretation
| Reaction Anti-A | Reaction Anti-B | Reaction Anti-AB | Interpretation Group |
| + | 0 | 0 | A |
| 0 | + | 0 | B |
| + | + | + | AB |
| 0 | 0 | 0 | O |
Key :
0 : No agglutination
+ : Agglutination
