Persons having anti-A and anti-B isoagglutinins in their serum belong to which blood group

**Core Concept**
The ABO blood group system is classified based on the presence or absence of **A** and **B antigens** on red blood cells and the corresponding **anti-A** and **anti-B isoagglutinins** in the serum. Individuals can be categorized into four main blood groups: A, B, AB, and O.

**Why the Correct Answer is Right**
The presence of both **anti-A** and **anti-B isoagglutinins** in the serum indicates that the individual lacks both A and B antigens on their red blood cells, as the immune system produces antibodies against foreign antigens. This combination is characteristic of individuals with **blood group O**, who have neither A nor B antigens on their red blood cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because individuals with blood group A have A antigens on their red blood cells and anti-B isoagglutinins in their serum.
**Option B:** This option is incorrect because individuals with blood group B have B antigens on their red blood cells and anti-A isoagglutinins in their serum.
**Option D:** This option is incorrect because individuals with blood group AB have both A and B antigens on their red blood cells and neither anti-A nor anti-B isoagglutinins in their serum.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that **blood group O** individuals are universal donors for red blood cell transfusions because their red blood cells lack A and B antigens, reducing the risk of an adverse reaction.

**Correct Answer:** D. Blood group O.