## **Core Concept**
Hyperacute graft rejection is an immediate and severe form of rejection that occurs within minutes to hours after transplantation. It is primarily mediated by pre-existing antibodies against the graft, often due to ABO blood group incompatibility or sensitization to human leukocyte antigens (HLA). This type of rejection is a major concern in organ transplantation.

## **Why the Correct Answer is Right**
The correct answer, within minutes to hours, reflects the immediate nature of hyperacute graft rejection. This rapid onset is due to the presence of pre-formed antibodies that quickly react with the endothelial cells of the graft's blood vessels, leading to activation of complement, thrombosis, and ischemia. This process can lead to graft failure within a very short period.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because hyperacute rejection does not occur within days; it happens much sooner.
- **Option B:** This option suggests a timeframe that is too long for hyperacute rejection, which occurs almost immediately.
- **Option D:** Similarly, this option suggests a timeframe that is more characteristic of acute rejection rather than hyperacute rejection.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that hyperacute rejection is often due to ABO incompatibility or pre-existing anti-HLA antibodies. This type of rejection is not effectively treated and usually results in graft loss. Pre-transplant cross-matching of donor and recipient blood is a critical step to prevent hyperacute rejection.

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