What characteristic would differentiate the appearance of insulin isophane suspension (NPH) from other insulins?

Insulin isophane suspension, commonly known as NPH (Neutral Protamine Hagedorn) insulin, is characterized by its cloudy appearance. This cloudiness is due to the presence of protamine, which is a protein that extends the action of insulin by slowing its absorption. Unlike regular insulin, which is clear, or glargine insulin, which can also be clear but has a different formulation, NPH's formulation results in a suspension that appears milky or cloudy when mixed properly.

The cloudiness signifies that the insulin contains particles that are not dissolved, which is expected in a suspension. This characteristic is essential for users to recognize, as it indicates proper formulation and helps in appropriate usage. NPH is often used for basal insulin coverage and requires careful handling to ensure the suspension is well-mixed before injection.