Hyperglycemia

Hyperglycemia, or high blood sugar, is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a glucose level higher than 10 mmol/l (180 mg/dl), but symptoms may not start to become noticeable until even higher values such as 15-20 mmol/l (270-360 mg/dl). However, chronic levels exceeding 7 mmol/l (125 mg/dl) can produce organ damage.

The origin of the term is Greek: hyper-, meaning excessive; -glyc-, meaning sweet; and -emia, meaning "of the blood".

Signs and symptoms

Temporary hyperglycemia is often benign and asymptomatic. Blood glucose levels can rise well above normal for significant periods without producing any permanent effects or symptoms. However, chronic hyperglycemia at levels more than slightly above normal can produce a very wide variety of serious complications over a period of years, including kidney damage, neurological damage, cardiovascular damage, damage to the retina etc.

In diabetes mellitus (by far the most common cause of chronic hyperglycemia), treatment aims at maintaining blood glucose at a level as close to normal as possible, in order to avoid these serious long-term complications.

Acute hyperglycemia involving glucose levels that are extremely high is a medical emergency and can rapidly produce serious complications (such as fluid loss through osmotic diuresis). It is most often seen in persons who have uncontrolled insulin-dependent diabetes.

The following symptoms may be associated with acute or chronic hyperglycemia, with the first three composing the classic hyperglycemic triad:

• Polyphagia - frequent hunger, especially pronounced hunger
• Polydipsia - frequent thirst, especially excessive thirst
• Polyuria - frequent urination
• Blurred vision
• Fatigue (sleepiness).
• Weight loss
• Poor wound healing (cuts, scrapes, etc.)
• Dry mouth
• Dry or itchy skin
• Tingling in feet or heels
• Erectile dysfunction
• Recurrent infections, external ear infections (swimmer's ear)
• Cardiac arrhythmia
• Stupor
• Coma

Frequent hunger without other symptoms can also indicate that blood sugar levels are too low. This may occur when people who have diabetes take too much oral hypoglycemic medication or insulin for the amount of food they eat. The resulting drop in blood sugar level to below the normal range prompts a hunger response. This hunger is not usually as pronounced as in Type I diabetes, especially the juvenile onset form, but it makes the prescription of oral hypoglycemic medication difficult to manage.

Polydipsia and polyuria occur when blood glucose levels rise high enough to result in excretion of excess glucose via the kidneys (glycosuria), producing osmotic diuresis.

Symptoms of Diabetic Ketoacidosis may include:

• Ketoacidosis
• Kussmaul hyperventilation: deep, rapid breathing
• Confusion or a decreased level of consciousness
• Dehydration due to glycosuria and osmotic diuresis
• Acute hunger and/or thirst
• 'Fruity' smelling breath odor
• Impairment of cognitive function, along with increased sadness and anxiety

Causes

Diabetes mellitus

Chronic hyperglycemia that persists even in fasting states is most commonly caused by diabetes mellitus, and in fact chronic hyperglycemia is the defining characteristic of the disease. Intermittent hyperglycemia may be present in prediabetic states. Acute episodes of hyperglycemia without an obvious cause may indicate developing diabetes or a predisposition to the disorder.

In diabetes mellitus, hyperglycemia is usually caused by low insulin levels (Diabetes mellitus type 1) and/or by resistance to insulin at the cellular level (Diabetes mellitus type 2), depending on the type and state of the disease. Low insulin levels and/or insulin resistance prevent the body from converting glucose into glycogen (a starch-like source of energy stored mostly in the liver), which in turn makes it difficult or impossible to remove excess glucose from the blood. With normal glucose levels, the total amount of glucose in the blood at any given moment is only enough to provide energy to the body for 20-30 minutes, and so glucose levels must be precisely maintained by the body's internal control mechanisms. When the mechanisms fail in a way that allows glucose to rise to abnormal levels, hyperglycemia is the result.

Drugs

Certain medications increase the risk of hyperglycemia, including corticosteroids, octreotide, beta blockers, epinephrine, thiazide diuretics, corticosteroids, niacin, pentamidine, protease inhibitors, L-asparaginase, and some antipsychotic agents. The acute administration of stimulants such as amphetamine typically produces hyperglycemia; chronic use, however, produces hypoglycemia. Some of the newer, double action anti-depressants such as Zyprexa (Olanzapine), and Cymbalta (Duloxetine), can also cause significant hyperglycemia.

Critical illness

A high proportion of patients suffering an acute stress such as stroke or myocardial infarction may develop hyperglycemia, even in the absence of a diagnosis of diabetes. Human and animal studies suggest that this is not benign, and that stress-induced hyperglycemia is associated with a high risk of mortality after both stroke and myocardial infarction.

Plasma glucose >120 mg/dl in the absence of diabetes is a clinical sign of sepsis.

Physical trauma, surgery and many forms of severe stress can temporarily increase glucose levels.

Physiological stress

Hyperglycemia occurs naturally during times of infection and inflammation. When the body is stressed, endogenous catecholamines are released that - amongst other things - serve to raise the blood glucose levels. The amount of increase varies from person to person and from inflammatory response to response. As such, no patient with first-time hyperglycemia should be diagnosed immediately with diabetes if that patient is concomitantly ill with something else. Further testing, such as a fasting plasma glucose, random plasma glucose, or two-hour postprandial plasma glucose level, must be performed.

Treatment

Treatment of hyperglycemia requires elimination of the underlying cause, e.g., treatment of diabetes when diabetes is the cause. Acute hyperglycemia can be treated by direct administration of insulin in most cases. Severe hyperglycemia can be treated with oral hypoglycemic therapy and lifestyle modification.