What is hyperglycemia?

Hyperglycemia is know as Diabetes mellitus.
It happens when the blood sugar increases and the conversion of glucose to glycogen decreases.
The main reason is that it is because of the pancreas.
To know why you should first know how the blood sugar level is controlled.i.e, How pancreas controls the blood sugar level.
First we can go to basics:
Pancreas secrete two kind of enzymes:
1.Insulin
2.Glucagon

Insulin is produced when beta cells in pancreas recognize the presence of high glucose level in blood. Insulin convert the excess Glucose to Glycogen and it is stored in liver.
Glucagon is released when alpha cells in pancreas recognize the absence or low sugar level in the blood. Then the Glucagon starts breaking down the Glycogen to Glucose. This brings back the normal blood sugar level.

Now lets come to our main point. Hyperglycemia is for due to "increase in blood sugar level" and "decrease in conversion of glucose to glycogen"
This case can be related with not releasing of Insulin. So if there is no conversion of glycogen. Then what is there for "Glucagon" to break down?
So we can come to know from this that the Pancreas is the main for controlling blood sugar level. So if there is a increase in blood sugar level then there is a problem with the pancreas. Now Insulin Tablets and injections are available in market to control Blood Sugar Level.