The insulin postprandial test measures the levels of sugar in the blood after two hours of having food. If a person has diabetes, it means the body is not able to make sufficient insulin to keep blood sugar in check. This can lead to high sugar levels in the blood which can further lead to serious health problems such as eye and nerve damage. This test tells how the body gives a response to sugar and starch after ingestion of a meal. As the food is digested in the stomach, the levels of blood sugar rise high. In response, the pancreas releases insulin so that the sugar is transferred from the blood to the cells of muscles and other tissues where it can be used as fuel. Ideally, within two hours of intake of a meal, the insulin and blood glucose levels should return to normal. In case, the blood glucose still remains high, there are chances that the person might have diabetes.