Blood sugar level
The blood sugar level, blood sugar concentration, blood glucose level, or glycemia is the measure of glucose concentrated in the blood. The body tightly regulates blood glucose levels as a part of metabolic homeostasis.
For a 70 kg human, approximately four grams of dissolved glucose is maintained in the blood plasma at all times. Glucose that is not circulating in the blood is stored in skeletal muscle and liver cells in the form of glycogen; in fasting individuals, blood glucose is maintained at a constant level by releasing just enough glucose from these glycogen stores in the liver and skeletal muscle in order to maintain homeostasis. Glucose can be transported from the intestines or liver to other tissues in the body via the bloodstream. Cellular glucose uptake is primarily regulated by insulin, a hormone produced in the pancreas. Once inside the cell, the glucose can now act as an energy source as it undergoes the process of glycolysis.
In humans, properly maintained glucose levels are necessary for normal function in a number of tissues, including the human brain, which consumes approximately 60% of blood glucose in fasting, sedentary individuals. A persistent elevation in blood glucose leads to glucose toxicity, which contributes to cell dysfunction and the pathology grouped together as complications of diabetes.
Glucose levels are usually lowest in the morning, before the first meal of the day, and rise after meals for an hour or two by a few millimoles per litre.
Abnormal persistently high glycemia is referred to as hyperglycemia; low levels are referred to as hypoglycemia. Diabetes mellitus is characterized by persistent hyperglycemia from a variety of causes, and it is the most prominent disease related to the failure of blood sugar regulation. Diabetes mellitus is also characterized by frequent episodes of low sugar, or hypoglycemia. There are different methods of testing and measuring blood sugar levels.
Drinking alcohol causes an initial surge in blood sugar and later tends to cause levels to fall. Also, certain drugs can increase or decrease glucose levels.
Units of measurement
In the United Kingdom and Commonwealth countries and ex-USSR countries, blood glucose measurements are expressed in molar concentration mmol/L abbreviated mM. In the United States, Germany, Japan and many other countries, they are expressed in mass concentration using mg/dL.Normal value range
Humans
Normal blood glucose level for non-diabetics should be 3.9–5.5 mmol/L.According to the American Diabetes Association, the fasting blood glucose target range for diabetics, should be 3.9–7.2 mmol/L and less than 10 mmol/L two hours after meals.
Normal value ranges may vary slightly between laboratories. Glucose homeostasis, when operating normally, restores the blood sugar level to a narrow range of about 4.4 to 6.1 mmol/L .
The global mean fasting plasma blood glucose level in humans is about 5.5 mmol/L ; however, this level fluctuates throughout the day. Blood sugar levels for those without diabetes and who are not fasting is usually below 6.9 mmol/L.
Despite widely variable intervals between meals or the occasional consumption of meals with a substantial carbohydrate load, human blood glucose levels tend to remain within the normal range. However, shortly after eating, the blood glucose level may rise, in non-diabetics, temporarily up to 7.8 mmol/L or slightly more.
The actual amount of glucose in the blood and body fluids is very small. In a healthy adult male of with a blood volume of 5 L, a blood glucose level of 5.5 mmol/L amounts to 5 g, equivalent to about a teaspoonful of sugar. Part of the reason why this amount is so small is that, to maintain an influx of glucose into cells, enzymes modify glucose by adding phosphate or other groups to it.
Other animals
In general, ranges of blood sugar in common domestic ruminants are lower than in many monogastric mammals. However this generalization does not extend to wild ruminants or camelids. For serum glucose in mg/dL, reference ranges of 42 to 75 for cows, 44 to 81 for sheep, and 48 to 76 for goats, but 61 to 124 for cats; 62 to 108 for dogs, 62 to 114 for horses, 66 to 116 for pigs, 75 to 155 for rabbits, and 90 to 140 for llamas have been reported. A 90 percent reference interval for serum glucose of 26 to 181 mg/dL has been reported for captured mountain goats, where no effects of the pursuit and capture on measured levels were evident. For beluga whales, the 25–75 percent range for serum glucose has been estimated to be 94 to 115 mg/dL. For the white rhinoceros, one study has indicated that the 95 percent range is 28 to 140 mg/dL. For harp seals, a serum glucose range of 4.9 to 12.1 mmol/L has been reported; for hooded seals, a range of 7.5 to 15.7 mmol/L has been reported.Regulation
The body's homeostatic mechanism keeps blood glucose levels within a narrow range. It is composed of several interacting systems, of which hormone regulation is the most important.There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels:
- catabolic hormones which increase blood glucose;
- and one anabolic hormone, which decreases blood glucose.
In order for blood glucose to be kept stable, modifications to insulin, glucagon, epinephrine and cortisol are made. Each of these hormones has a different responsibility to keep blood glucose regulated; when blood sugar is too high, insulin tells muscles to take up excess glucose for storage in the form of glycogen. Glucagon responds to too low of a blood glucose level; it informs the tissue to release some glucose from the glycogen stores. Epinephrine prepares the muscles and respiratory system for activity in the case of a "fight or flight" response. Lastly, cortisol supplies the body with fuel in times of heavy stress.
Abnormalities
High blood sugar
If blood sugar levels remain too high the body suppresses appetite over the short term. Long-term hyperglycemia causes many health problems including heart disease, cancer, eye, kidney, and nerve damage.Blood sugar levels above 16.7mmol/L can cause fatal reactions. Ketones will be very high initiating ketoacidosis. The ADA recommends seeing a doctor if blood glucose reaches 13.3 mmol/L, and it is recommended to seek emergency treatment at 15mmol/L blood glucose if Ketones are present. The most common cause of hyperglycemia is diabetes. When diabetes is the cause, physicians typically recommend an anti-diabetic medication as treatment. From the perspective of the majority of patients, treatment with an old, well-understood diabetes drug such as metformin will be the safest, most effective, least expensive, and most comfortable route to managing the condition. Treatment will vary for the distinct forms of Diabetes and can differ from person to person based on how they are reacting to treatment. Diet changes and exercise implementation may also be part of a treatment plan for diabetes.
Some medications may cause a rise in blood sugars of diabetics, such as steroid medications, including cortisone, hydrocortisone, prednisolone, prednisone, and dexamethasone.
Low blood sugar
When the blood sugar level is below 70 mg/dL, this is referred to as having low blood sugar. Low blood sugar is very frequent among type 1 diabetics. There are several causes of low blood sugar, including, taking an excessive amount of insulin, not consuming enough carbohydrates, drinking alcohol, spending time at a high elevation, puberty, and menstruation. If blood sugar levels drop too low, a potentially fatal condition called hypoglycemia develops. Symptoms may include lethargy, impaired mental functioning; irritability; shaking, twitching, weakness in arm and leg muscles; pale complexion; sweating; loss of consciousness.Mechanisms that restore satisfactory blood glucose levels after extreme hypoglycemia must be quick and effective to prevent extremely serious consequences of insufficient glucose: confusion or unsteadiness and, in the extreme loss of consciousness and seizures. Without discounting the potentially quite serious conditions and risks due to or oftentimes accompanying hyperglycemia, especially in the long-term, it is still generally more dangerous to have too little glucose – especially if levels are very low – in the blood than too much, at least temporarily, because glucose is so important for metabolism and nutrition and the proper functioning of the body's organs. This is especially the case for those organs that are metabolically active or that require a constant, regulated supply of blood sugar. Symptomatic hypoglycemia is most likely associated with diabetes and liver disease, without treatment or with wrong treatment, possibly in combination with carbohydrate malabsorption, physical over-exertion or drugs. Many other less likely illnesses, like cancer, could also be a reason. Starvation, possibly due to eating disorders, like anorexia, will also eventually lead to hypoglycemia. Hypoglycemic episodes can vary greatly between persons and from time to time, both in severity and swiftness of onset. For severe cases, prompt medical assistance is essential, as damage to brain and other tissues and even death will result from sufficiently low blood-glucose levels.