What is often a cause of rapid hyperkalemia aside from renal failure?

The correct answer is massive cell destruction, which can lead to rapid hyperkalemia due to the release of potassium from inside the cells into the extracellular space. This process can occur in conditions where there is extensive tissue damage or death, such as in hemolysis, severe trauma, burns, or tumor lysis syndrome. When a large number of cells are compromised, the potassium that was previously contained within the cells is released into the bloodstream, resulting in elevated serum potassium levels.

In contrast, a chronic low-protein diet primarily affects the body's metabolic processes over time rather than causing an acute increase in potassium levels. Mild exercise usually helps to regulate potassium levels, as it can enhance cellular uptake. Viral infections may cause mild fluctuations in potassium levels but are not typically associated with rapid, severe hyperkalemia unless accompanied by massive tissue destruction or other complicating factors.