**Question:** All of the following cause intravascular hemolysis, except

A. Direct hemolysis
B. Indirect hemolysis
C. Hemolysis due to immune complex deposition
D. Hemolysis due to microangiopathy

**Core Concept:**
Intravascular hemolysis is the process by which red blood cells (RBCs) are broken down within the blood vessels. This can be due to various causes, which can be broadly categorized into direct or indirect mechanisms. Direct hemolysis involves RBC membrane damage, while indirect hemolysis involves RBC membrane-independent mechanisms. Additionally, there are other causes of hemolysis that do not fit into the direct or indirect categories.

**Why the Correct Answer is Right:**
Option C, "Hemolysis due to immune complex deposition," is incorrect because immune complex deposition primarily leads to extravascular hemolysis, where the immune complexes deposit in tissues and activate the complement system, causing RBC destruction in the interstitial spaces rather than within the blood vessels.

Option D, "Hemolysis due to microangiopathy," is incorrect because microangiopathy typically refers to diseases or processes affecting small blood vessels (microcirculation). While microangiopathy can cause intravascular hemolysis, the term itself is not an appropriate description for the mechanism causing hemolysis in this case.

Option A, "Direct hemolysis," falls under the category of intravascular hemolysis as it involves direct damage to RBCs, leading to their destruction within the blood vessels.

Option B, "Indirect hemolysis," also falls under the category of intravascular hemolysis, as it involves RBC membrane-independent mechanisms causing RBC destruction within the blood vessels.

**Why Each Wrong Option is Incorrect:**
Option C (immune complex deposition) is wrong because it primarily causes extravascular hemolysis.
Option D (microangiopathy) is wrong because it is a broader term for diseases affecting small blood vessels and does not specifically describe the hemolysis mechanism.
Option A (direct hemolysis) is correct because it involves direct damage to RBCs, leading to their destruction within the blood vessels.
Option B (indirect hemolysis) is correct because it involves RBC membrane-independent mechanisms causing RBC destruction within the blood vessels.

**Clinical Pearl:** Intravascular hemolysis is a crucial concept in understanding various clinical scenarios involving RBC destruction within blood vessels. Common causes of intravascular hemolysis include autoimmune disorders, infections, and drug reactions. Recognizing the cause of intravascular hemolysis can help guide diagnosis and management strategies for patients presenting with hemolysis syndromes.