**Core Concept**
TRALI (Transfusion-Related Acute Lung Injury) is a serious complication of blood transfusion characterized by non-cardiogenic pulmonary edema. It is a leading cause of transfusion-related mortality, and prompt recognition is crucial for effective management.

**Why the Correct Answer is Right**
TRALI typically occurs within 6 hours after blood transfusion, with symptoms appearing within 1-3 hours. This time frame is critical for clinicians to recognize the condition and initiate appropriate treatment. The pathophysiology of TRALI involves the transfer of biologically active lipids and proteins from donor plasma to recipient lungs, leading to activation of neutrophils and release of inflammatory mediators, resulting in acute lung injury.

**Why Each Wrong Option is Incorrect**
**Option A:** Less than 6 hours - This option is incorrect because the typical onset of TRALI is usually observed within 6 hours, not before.
**Option B:** 12 hours or more - This option is incorrect because TRALI symptoms usually appear within 6 hours, not after 12 hours or more.
**Option C:** Within 30 minutes - This option is incorrect because TRALI symptoms typically do not appear within 30 minutes of blood transfusion, but rather within 1-3 hours.

**Clinical Pearl / High-Yield Fact**
TRALI is often associated with the transfusion of blood products from female donors, particularly those with high levels of anti-HLA or anti-neutrophil antibodies.

**Correct Answer: C. Within 6 hours.**