## **Core Concept**
Hyperacute rejection is a type of organ transplant rejection that occurs almost immediately after transplantation. It is primarily mediated by pre-existing antibodies in the recipient against the donor organ. This rapid response leads to severe damage and often necessitates immediate removal of the graft.

## **Why the Correct Answer is Right**
Hyperacute rejection occurs within minutes to hours after transplantation. This timeframe is critical because it is a result of the immediate reaction of the recipient's immune system to the graft, recognizing it as foreign due to pre-formed antibodies against the donor's human leukocyte antigens (HLA) or ABO blood group antigens. The presence of these antibodies leads to activation of complement, coagulation, and inflammation within the graft, resulting in rapid dysfunction.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a timeframe that is too long for hyperacute rejection, which is known for its immediate onset.
- **Option B:** Similarly, this option also suggests a delayed onset that does not align with the definition of hyperacute rejection.
- **Option D:** This option suggests an even longer timeframe, which is more characteristic of chronic rejection processes.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that hyperacute rejection is often due to ABO incompatibility or sensitization to HLA antigens. A crucial preventive measure is cross-matching donor and recipient blood before transplant to minimize this risk. Despite precautions, when hyperacute rejection occurs, it is a medical emergency requiring prompt intervention.

## **Correct Answer:** . minutes to hours