In human blood grouping, a universal recipient is a person who belongs to which ABO blood group?

Introduction / Context:
The terms universal donor and universal recipient are basic concepts in human blood transfusion. They relate to which blood groups can safely donate blood to or receive blood from other groups in the ABO system. This question focuses on the universal recipient, asking which blood group can, in an emergency and with standard compatibility rules, receive blood from any of the main ABO groups.

Given Data / Assumptions:

- We are dealing with the ABO blood group system. - The term used is universal recipient. - Options given are AB, O, B and A. - We assume Rh factor is either matched or not considered for this simplified question.

Concept / Approach:
In the ABO system, blood group AB has both A and B antigens on the surface of its red blood cells and does not have anti A or anti B antibodies in its plasma. This means that an individual with group AB blood can receive red blood cells from donors with groups A, B, AB or O, provided that other factors like Rh are matched. Therefore, group AB is called the universal recipient group. Group O is instead known as the universal donor because its red cells lack A and B antigens.

Step-by-Step Solution:
1. Recall that blood groups are determined by the presence or absence of A and B antigens on red blood cells. 2. Group AB has both A and B antigens but no anti A or anti B antibodies. 3. Because the plasma of an AB person does not attack A or B antigens, they can safely receive red cells from all ABO groups. 4. Group O, by contrast, has no A or B antigens but has both anti A and anti B antibodies, making it unsafe to receive other types but safe to donate red cells to others. 5. Groups A and B can receive from limited groups only, not from all four. 6. Therefore, the universal recipient group is AB.

Verification / Alternative check:
Basic biology textbooks and healthcare educational material always state that group O negative is the universal donor for red cells, and group AB positive is considered the universal recipient, particularly in the context of ABO compatibility. Many exam questions repeat this pairing, making it a standard fact for students to memorise. Reviewing such material quickly confirms that AB is the correct answer in the ABO system for universal recipient status.

Why Other Options Are Wrong:
Group O is popularly known as the universal donor because its red cells lack A and B antigens and can be given to patients of any ABO group. However, people with group O blood cannot receive from all other groups due to the presence of both anti A and anti B antibodies in their plasma. Groups A and B each have one type of antigen and one corresponding antibody, so their recipients are limited to compatible groups only. Consequently, none of these groups can receive blood from every other group, so they are not universal recipients.

Common Pitfalls:
Candidates sometimes confuse universal donor with universal recipient and may incorrectly select group O based on that confusion. Another error is to think that the most common blood group in a population must be the universal recipient, which is not logically correct. To avoid these mistakes, students should clearly separate the concepts: O as universal donor for red cells in ABO terms, and AB as universal recipient. Creating a simple mental table of antigens and antibodies for each group also helps solidify this understanding.

Final Answer:
In the ABO blood group system, the universal recipient belongs to blood group AB.