Final answer:
Hyperglycemia is primarily caused by a lack of insulin or reduced insulin sensitivity, leading to conditions like diabetes mellitus. It can also be exacerbated by high carbohydrate intake, stress, and other factors.
Step-by-step explanation:
The primary cause of hyperglycemia is a lack of insulin, which leads to conditions such as diabetes mellitus. When there are low levels of insulin production by the pancreas or reduced sensitivity of cells to insulin, glucose cannot be adequately absorbed by cells, resulting in high levels of blood glucose. Additionally, high carbohydrate intake, stress, and other factors such as certain medications, can also cause hyperglycemia. It's important to manage blood glucose levels through diet, exercise, and potentially medications or insulin therapy to prevent complications associated with this condition.