Hyperglycemia is the term for abnormally high blood glucose levels. In a person without diabetes mellitus (sugar diabetes), hyperglycemia is unlikely to occur unless it is triggered by severe stress, injury or the use of medication.
Even in these instances, it is temporary and will quickly resolve, with or without medical intervention, once the causative factors are removed or neutralized. With diabetes mellitus, however, hyperglycemia persists for prolonged periods of time due to the lack of insulin or inability of insulin to act and reduce the blood glucose levels. Hypoglycemia on the other end is abnormally low blood glucose levels and occurs frequently if food intake is minimal even without any underlying pathology.
There is a common misconception that the blood glucose level in a healthy person spikes well beyond the norm after meals. This, however, is untrue. While the blood glucose levels may reach the upper limits of the normal range, the body’s regulating mechanisms ensure that normal levels are maintained. Excessively high blood glucose levels can disrupt homeostasis and cause cell damage so the body ensures that this is avoided. It is able to do this by stimulating the cells to take up glucose from the blood stream, promote glucose storage, reduce gastric emptying and intestinal absorption as well as affecting the appetite to limit further food intake. This is explained in detail under normal blood glucose.
The blood glucose levels are not static and fluctuate throughout the day. The body aims to maintain a blood glucose level within a minimum of 70mg/dL (3.9 mmol/L) to a maximum of 140 mg/dL (7.8 mmol/L). Usually these extremes are not reached and the levels are maintained between 90mg/dL and 120mg/dL. The lowest glucose levels are recorded prior to meals (pre-prandial) and the highest are recorded 1 to 2 hours after meals (post-prandial). For diabetics, the minimum and maximum range may extend further due the inability of the body to regulate the glucose levels.
Signs and Symptoms of Hyperglycemia
The symptoms of hyperglycemia may not always be as obvious as hypoglycemia (low blood glucose levels) because the body is able to tolerate elevated blood glucose levels for a period of time. With hypogylcemia on the other hand, the limited availability of glucose quickly affects normal functioning and produces symptoms that are apparent almost immediately. It is only after a couple hours of high blood glucose levels that the symptoms of hyperglycemia become evident. Therefore, most people with temporary elevation of blood glucose levels will experience no symptoms.
The signs and symptoms can be divided into short-, mid- and long-term features. In the early stages of hyperglycemia, there may be no symptoms or a person may complain of headaches as brain tissue is highly sensitive to changes in glucose levels. This can occur within the first few hours or a day or two of hyperglycemia.
After a few days, the mid-stage signs and symptoms will become evident and includes :
- Excessive thirst (polydipsia) and excessive urination (polyuria) are seen as a result of the diuretic effect of glucose (osmotic diuresis).
- Dry mouth may also be present, especially with prolonged fluid loss.
- Dehydration is uncommon but may be seen to varying degrees although it is usually mild.
- Increased appetite often accompanied by weight loss.
- Fatigue, drowsiness and itchy skin may be seen towards the medium to long term stages.
Long term effects of hyperlglycemia are the same as diabetic complications. This includes :
- Blurry vision
- High blood pressure
- Elevated blood lipid levels
- Poor wound healing
- Diminished sensation
Very high blood glucose levels can produce severe symptoms within hours or days.
- Severe dehydration
- Shortness of breath
Article reviewed by Dr. Greg. Last updated on March 9, 2011