Blood Grouping Practical – Principle, Procedure & Precautions (BHMS Practical Notes)
Introduction
Blood grouping is an essential laboratory procedure used to identify a person’s blood type based on the ABO and Rh systems.
BHMS students must understand this practical because it links immunology, hematology, and clinical laboratory science. Blood grouping is widely used in transfusion practice, medico-legal work, and understanding antigen–antibody reactions.
This note provides a clear explanation for exams, journals, and viva preparation.
1. Principle of Blood Grouping
Blood grouping is based on an antigen–antibody reaction.
ABO System
RBCs may contain Antigen A, B, both (AB), or none (O).
The serum contains naturally occurring antibodies anti-A and/or anti-B.
Example:
Group A → A antigen on RBC, anti-B in plasma
Group B → B antigen on RBC, anti-A in plasma
Rh System
* If the RBC surface carries **D antigen**, the person is **Rh positive (Rh⁺)**.
* Absence of D antigen → **Rh negative (Rh⁻)**.
Basic Immunological Principle
When **specific antibodies** mix with their corresponding **antigens**, **agglutination (clumping)** occurs.
* Agglutination = **presence** of antigen
* No agglutination = **absence** of antigen
This reaction forms the basis of determining blood type.
2. Requirements / Materials
* Clean glass slide or tile
* Anti-A serum (blue)
* Anti-B serum (yellow)
* Anti-D serum (clear) for Rh typing
* Sterile lancet
* Alcohol swab
* Toothpicks or applicator sticks
* Dropper
* Cotton swab
* Gloves
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3. Procedure (Slide Method — Common for BHMS Practical)
## **Step-by-Step Method**
1. Preparation
* Clean the fingertip with an alcohol swab.
* Prick the finger with a sterile lancet.
* Wipe away the first drop of blood.
2. Labeling the Slide
Divide the slide into 3 sections and label:
* **A** (for Anti-A serum)
* **B** (for Anti-B serum)
* **D** (for Anti-D serum)
3. Placing Reagents
Place one drop of:
* Anti-A serum in section A
* Anti-B serum in section B
* Anti-D serum in section D
4. Adding Blood
Place a small drop of blood next to each reagent.
5. Mixing
Mix blood and serum in each section using separate applicator sticks to avoid contamination.
6. Observation
Gently rock the slide and observe for **agglutination** within 1–2 minutes.
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4. Interpretation of Results
| **Anti-A** | **Anti-B** | **Anti-D** | **Blood Group** |
| ---------------- | ---------------- | ---------- | --------------- |
| Agglutination | No agglutination | +/- | **A** (+ / –) |
| No agglutination | Agglutination | +/- | **B** (+ / –) |
| Agglutination | Agglutination | +/- | **AB** (+ / –) |
| No agglutination | No agglutination | +/- | **O** (+ / –) |
Examples
* Anti-A +, Anti-B –, Anti-D + → **A positive**
* Anti-A –, Anti-B –, Anti-D – → **O negative**
* Anti-A +, Anti-B +, Anti-D – → **AB negative**
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5. Precautions
Follow these strictly — mistakes here cause wrong grouping.
1. Use **fresh anti-sera** only.
2. Use **separate sticks** for mixing in each section.
3. Avoid excess blood; too much can mask agglutination.
4. Do not mix reagents; contamination gives false results.
5. Read agglutination **within 2 minutes**; delayed reading is unreliable.
6. Ensure slide is **clean and dry** before starting.
7. Do not expose reagents to heat or sunlight.
8. Do not shake vigorously — gentle rocking is enough.
9. Maintain proper lighting while observing reactions.
10. Dispose lancet and cotton safely to maintain lab hygiene.
6. Clinical Significance (Academic Only)
* Blood grouping is essential for **safe blood transfusion**.
* Helps identify **maternal–fetal incompatibility** (Rh factor).
* Used in **forensic identification** and **organ transplantation**.
* Important for understanding **immunological reactions** in pathology.
*(Note: This section is purely educational and does not provide medical or diagnostic advice.)*
7. Viva Questions (Useful for BHMS Students)**
**Q1. What is agglutination?**
A: Clumping of RBCs due to antigen–antibody reaction.
**Q2. Which antibody determines the Rh factor?**
A: Anti-D antibody.
**Q3. What is the universal donor?
A: O negative (O⁻).
**Q4. What is the universal recipient?
A: AB positive (AB⁺).
**Q5. Why wipe the first drop of blood?
A: It contains tissue fluids and may dilute the sample.
Conclusion
Blood grouping is a fundamental laboratory test based on antigen–antibody reactions.
Understanding the principle, performing the slide method correctly, and following essential precautions help BHMS students master this practical for exams, viva, and journal preparation.
