**Question:** Which of the following is not seen in sickle cell disease

A. Acidosis
B. Anemia
C. Hyperbilirubinemia
D. Increased red blood cell destruction

**Core Concept:** Sickle cell disease is an inherited blood disorder caused by a genetic mutation in the HBB gene, resulting in the production of abnormal hemoglobin (HbS) instead of normal hemoglobin (HbA). HbS is a variant of hemoglobin that polymerizes under low oxygen tension, leading to the formation of sickle-shaped red blood cells. This shape change distorts blood vessels, causing pain, organ damage, and reduced blood flow.

**Why the Correct Answer is Right:** In sickle cell disease, the primary manifestation is the formation of sickle-shaped red blood cells due to HbS polymerization. This leads to anemia, increased red blood cell destruction, and acidosis as a consequence of impaired oxygen delivery and tissue hypoxia. Hyperbilirubinemia is not a direct result of sickle cell disease, but rather a complication from hemolysis (increased red blood cell breakdown) and jaundice.

**Why Each Wrong Option is Incorrect:**

A. Acidosis: As mentioned above, acidosis is a consequence of reduced oxygen delivery and tissue hypoxia, not a direct result of the presence of HbS.
B. Anemia: Although anemia is a common feature due to the destruction of red blood cells, it is not a direct result of HbS polymerization.
C. Hyperbilirubinemia: Hyperbilirubinemia occurs due to increased red blood cell breakdown (hemolysis) in sickle cell disease, not directly related to HbS polymerization.

**Clinical Pearl:** Sickle cell disease is a complex disease with a range of clinical manifestations, many of which are indirect consequences of HbS polymerization. Understanding the underlying pathophysiology is crucial for accurate diagnosis and appropriate management of this genetic disorder.