**Question:** An 18-year-old man is rushed to the emergency room in shock following a motor vehicle accident. He is transfused with 5 U of blood. Following the transfusion the patient complains of fever, nausea, vomiting, and chest pain. Laboratory data show elevated indirect serum bilirubin, decreased serum haptoglobin, and a positive Coombs test. Which of the following is the most likely diagnosis?

A. Autoimmune Hemolytic Anemia
B. Aplastic Anemia
C. Hemolytic Anemia
D. Sickle Cell Anemia

**Correct Answer:** D. Sickle Cell Anemia

**Core Concept:**
Autoimmune Hemolytic Anemia, Aplastic Anemia, Hemolytic Anemia, and Sickle Cell Anemia are all types of anemia, characterized by a decrease in the number of red blood cells or their functional capacity. However, the correct answer refers to a specific genetic disorder.

**Why the Correct Answer is Right:**
Sickle Cell Anemia (SCA) is an inherited disorder resulting from a single gene mutation. It is characterized by the production of abnormal hemoglobin (HbS) instead of the normal hemoglobin (HbA). HbS polymerizes under low oxygen tension, causing RBCs to become rigid and sickle-shaped, leading to hemolysis, anemia, and pain crises.

**Why Each Wrong Option is Incorrect:**

A. Autoimmune Hemolytic Anemia (AHA) is caused by the immune system attacking and destroying red blood cells, resulting in anemia. The correct answer is not autoimmune in nature.

B. Aplastic Anemia is characterized by a deficiency in the production of all blood cells (red, white, and platelets). The correct answer focuses on hemolysis, not hematopoietic stem cell dysfunction.

C. Hemolytic Anemia is a type of anemia resulting from the destruction of RBCs. While this is relevant, the correct answer is more specific to Sickle Cell Anemia.

D. Sickle Cell Anemia (SCA) is a genetic disorder caused by the production of abnormal hemoglobin S (HbS) leading to RBCs becoming sickle-shaped and causing hemolysis, pain crises, and anemia. The correct answer highlights the genetic cause and the resulting effects, unlike the other options.

**Clinical Pearls:**

1. Sickle Cell Anemia is a common genetic disorder prevalent in individuals of African, Mediterranean, and Middle Eastern descent.
2. Pain crises are common manifestations of SCA, which can lead to complications like acute chest syndrome, ischemic pain, and stroke.
3. Transfusion therapy is crucial for managing severe anemia and preventing complications in SCA patients.