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Hyperglycemia, hyperglycaemia, or high blood sugar is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood glucose level of 10+ mmol/l (180 mg/dl), but symptoms may not start to become noticeable until later numbers such as 15-20+ mmol/l (270-360 mg/dl)or 15.2-32.6 mmol/l. However, chronic levels exceeding 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".
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 and/or by resistance to insulin at the cellular level, 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.
Certain medications increase the risk of hyperglycemia, including 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.
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.
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.
Glucose levels are measured in either:
Scientific journals are moving towards using mmol/l; some journals now use mmol/l as the primary unit but quote mg/dl in parentheses.
Glucose levels vary before and after meals, and at various times of day; the definition of "normal" varies among medical professionals. In general, the normal range for most people (fasting adults) is about 80 to 110 mg/dl or 4 to 6 mmol/l. A subject with a consistent range above 126 mg/dl or 7 mmol/l is generally held to have hyperglycemia, whereas a consistent range below 70 mg/dl or 4 mmol/l is considered hypoglycemic. In fasting adults, blood plasma glucose should not exceed 126 mg/dl or 7 mmol/l. Sustained higher levels of blood sugar cause damage to the blood vessels and to the organs they supply, leading to the complications of diabetes.
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 comprising the classic hyperglycaemic triad:
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.
Symptoms of Diabetic Ketoacidosis may include:
Treatment of hyperglycemia requires elimination of the underlying cause, e.g., treatment of diabetes when diabetes is the cause. Acute and severe hyperglycemia can be treated by direct administration of insulin in most cases, under medical supervision.