Everything about Blood Glucose totally explained
Blood sugar is the amount of
glucose in the blood. Glucose, transported via the bloodstream, is the primary source of energy for the body's cells.
Blood sugar concentration, or glucose level, is tightly
regulated in the human body. Normally, the blood glucose level is maintained between about 4 and 6 mmol/L. Normal blood glucose level (homoeostasis) is about 90mg/100ml or 5mM. The total measurement of glucose in the circulating blood is therefore about 3.3 to 7g (assuming an ordinary adult blood volume of 5 liters). Glucose levels rise after meals and are usually lowest in the morning, before the first meal of the day.
Failure to maintain blood glucose in the normal range leads to conditions of persistently high (
hyperglycemia) or low (
hypoglycemia) blood sugar.
Diabetes mellitus, characterized by persistent hyperglycemia of several causes, is the most prominent disease related to failure of blood sugar regulation.
Although it's called "blood sugar," sugars besides glucose are found in the blood, such as
fructose and
galactose. Only glucose levels are regulated via
insulin and
glucagon.
Normal values
Despite long intervals between meals or the occasional consumption of meals with a substantial
carb load, human blood glucose levels normally remain within a remarkably narrow range. In most humans this varies from about 80 mg/dl to perhaps 120 mg/dl (3.9 to 6.0
mmol/litre) except shortly after eating when the blood glucose level rises temporarily (up to 140 mg/dl in a non-diabetic).
It is usually a surprise to realize how little glucose is actually maintained in the blood and body fluids. The control mechanism works on very small quantities. In a healthy adult male of 75
kg (165.35
lb) with a
blood volume of 5
litres (1.32
gal), a blood glucose level of 100 mg/dl or 5.5 mmol/l corresponds to about 5 g (0.2
oz or 0.002
gal, 1/500 of the total) of glucose in the blood and approximately 45 g (1½
ounces) in the total
body water (which obviously includes more than merely blood and will be usually about 60% of the total
body weight in men). A more familiar comparison may help – 5 grams of glucose is about equivalent to a commercial sugar packet (as provided in many restaurants with
coffee or
tea).
Regulation
The
homeostatic effect that keeps the blood value of glucose in a remarkably narrow range is the result of many factors, of which hormone regulation is the most important.
There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels:
- catabolic hormones (such as glucagon, growth hormone, and catecholaminesthyroxine, somatostatin), which increase blood glucose
- and one anabolic hormone (insulin), which decreases blood glucose. aac to aamir & abid glucose level is approx. 85.5- 134.5(in research)
Glucose measurement
Sample type
Glucose can be measured in whole blood,
serum, or
plasma. Historically, blood glucose values were given in terms of whole blood, but most laboratories now measure and report the
serum glucose levels. Because
RBC (
erythrocytes) have a higher concentration of protein (for example hemoglobin) than serum, serum has a higher water content and consequently more dissolved glucose than does whole blood. To convert from whole-blood glucose, multiply the value by 1.15 to give the serum/plasma level.
Collection of blood in clot (
red-top) tubes for serum chemistry analysis permits the metabolism of glucose in the sample by blood cells until separated by
centrifugation. Higher than normal amounts of
white or
red blood cell counts can lead to excessive
glycolysis in the sample with substantial reduction of glucose level if the sample isn't processed quickly. Ambient temperature at which the blood sample is kept prior to centrifugation and separation of Plasma/Serum also affects glucose levels. At refrigerator temperatures, glucose remains relatively stable for several hours in the blood sample. At room temperature (25 °C), a loss of 1 to 2% of glucose per hour should be expected. The loss of glucose levels in aforementioned conditions can be prevented by using Fluoride top (gray-top) as the anticoagulant of choice upon blood collection, as Fluoride inhibits glycolysis. However, this should only be used when blood will be transported from one hospital laboratory to another for glucose measurement. Red-top serum separator tubes also preserve glucose in samples once they've been centrifugated to isolate the serum from cells, this tube would be the most efficient. Particular care should be given to drawing blood samples from the arm opposite the one in which an intravenous line is inserted, to prevent contamination of the sample with
intravenous fluids (IV). Alternatively, blood can be drawn from the same arm with an IV line after the IV was turned off for at least 5 minutes and the arm is elevated to drain the infused fluids away from the vein. As little as 10% contamination with 5%
dextrose (D5W) will elevate glucose in a sample by 500 mg/dl or more. Arterial, capillary and venous blood have comparable glucose levels in a fasting individual, whereas after meals venous levels are lower than capillary or arterial blood.
Methodology
There are two different major methods that have been used to measure glucose. The older one is a chemical method that exploits the
nonspecific reducing property of glucose in a reaction with an indicator substance that acquires or changes color on its reduction. Since other blood compounds also have reducing properties (for example, urea, which can build up in uremic patients), this method can have erroneous measurements up to 5 to 15 mg/dl. This is solved by the Enzymatic methods that are highly specific for glucose. The two most common employed enzymes are
glucose oxidase and
hexokinase.
| I. CHEMICAL METHODS |
| A. Oxidation-Reduction Reaction |
|
|
| NADP as cofactor
NADPH (reduced product) is measured in 340 nm
More specific than Glucose Oxidase method due to G-6PO_4, which inhibits interfering substances except when sample is hemolyzed
|
Laboratory tests
Fasting Blood Sugar or Glucose test (FBS)
Urine Glucose test
Two-hr Postprandial Blood Sugar Test (2-h PPBS)
Oral Glucose Tolerance test (OGTT)
Intravenous Glucose Tolerance test (IVGTT)
Glycosylated Hemoglobin (HbA1C)
Self-monitoring of Glucose level via Home Kits
Clinical correlation
The fasting blood glucose (FBG) level is the most commonly used indication of overall glucose homeostasis. Conditions that affect glucose levels are shown in the table below. They reflect abnormalities in the multiple control mechanism of glucose regulation.
The metabolic response to a carbohydrate challenge is conveniently assessed by the postprandial glucose level drawn 2 hours after a meal or a glucose load. In addition, the glucose tolerance test, consisting of serial timed measurements after a standardized amount of oral glucose intake, is used to aid in the diagnosis of diabetes.
Health effects
If blood sugar levels drop too low, a potentially fatal condition called hypoglycemia develops. Symptoms may include lethargy, impaired mental functioning, irritability, and loss of consciousness.
If levels remain too high, appetite is suppressed over the short term. Long-term hyperglycemia causes many of the long-term health problems associated with diabetes, including eye, kidney, and nerve damage.
Low blood sugar
Some people report drowsiness or impaired cognitive function several hours after meals, which they believe is related to a drop in blood sugar, or "low blood sugar". For more information, see:
idiopathic postprandial syndrome
hypoglycemia
Mechanisms which restore satisfactory blood glucose levels after hypoglycemia must be quick and effective, because of the immediate serious consequences of insufficient glucose (in the extreme, coma, less immediately dangerous, confusion or unsteadiness, amongst many other effects). This is because, at least in the short term, it's far more dangerous to have too little glucose in the blood than too much. In healthy individuals these mechanisms are indeed generally efficient, and symptomatic hypoglycemia is generally only found in diabetics using insulin or other pharmacological treatment. Such hypoglycemic episodes vary greatly between persons and from time to time, both in severity and swiftness of onset. In 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.
Converting glucose units
The U.S. use mg/dL. The rest of the world, including Canada and Mexico, uses what is referred to as the "World Standard" of mmol/L.
To convert blood glucose readings:
Divide the mg/dL by 18 to get mmol/L (or multiply by 0.055).
Multiply the mmol/L by 18 to get mg/dL (or divide with 0.055).Further Information
Get more info on 'Blood Glucose'.
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