**Core Concept**
Increased blood viscosity is a condition where blood becomes thicker and more resistant to flow, potentially leading to circulatory problems. This can be caused by an imbalance in plasma water and solute content, red blood cell (RBC) aggregation, or the presence of abnormal proteins.

**Why the Correct Answer is Right**
Multiple myeloma is a type of plasma cell disorder characterized by the overproduction of monoclonal immunoglobulins (M-protein) by malignant plasma cells. These abnormal proteins can accumulate in the blood and contribute to increased blood viscosity. The M-protein molecules can also cause RBC aggregation, further exacerbating the condition. This leads to a decrease in blood flow and potentially life-threatening complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Fasting state typically leads to decreased blood viscosity due to dehydration, which concentrates the blood and increases its viscosity. However, the effect is temporary and usually not severe enough to cause significant clinical concern.

**Option B:** Hypoglycemia (low blood sugar) is not directly related to blood viscosity. It can cause various symptoms, including confusion, tremors, and tachycardia, but does not affect blood viscosity.

**Option D:** Amyloidogenesis refers to the accumulation of amyloid fibrils in tissues, which can occur in various diseases, including Alzheimer's disease. While amyloid deposition can lead to organ dysfunction, it does not directly affect blood viscosity.

**Clinical Pearl / High-Yield Fact**
Keep in mind that increased blood viscosity is a potential complication of multiple myeloma and other plasma cell disorders. Recognizing the relationship between M-protein production and blood viscosity can help you diagnose and manage patients with these conditions more effectively.

**✓ Correct Answer: C. Multiple myeloma**