Blood sugar

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For the 2007 Pendulum single, see Blood Sugar/Axle Grinder .

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 is 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.

1 Normal values
2 Regulation
3 Glucose measurement
4 Health effects
5 Low blood sugar
6 Converting glucose units
7 References
8 See also

[edit] 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)^{[citation needed]} 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).

[edit] 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)

[edit] Glucose measurement

[edit] 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 (i.e. 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 is not 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 have 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.

[edit] 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 (e.g., 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
$Glucose + Alkaline Copper Tartarate\xrightarrow{Reduction} Cuprous Oxide$
1. Alkaline Copper Reduction
Folin Wu Method	$Cu^{++} + Phosphomolybdic Acid\xrightarrow{Oxidation} Phosphomolybdenum Oxide$	Blue end-product
Benedict's method	Modification of Folin wu for Qualitative Urine Glucose
Nelson Somoygi Method	$Cu^{++} + Arsenomolybdic Acid\xrightarrow{Oxidation} Arsenomolybdenum Oxide$	Blue end-product
Neocuproine Method	$Cu^{++} + Neocuproine\xrightarrow{Oxidation} Cu^{++} Neocuproine Complex$ *	Yellow-orange color Neocuproine
Shaeffer Hartmann Somygi	Utilizes the principle of Iodine reaction with Cuprous byproduct. Excess I₂ is then titrated with thiosulfate.
2. Alkaline Ferricyanide Reduction
Hagedorn Jensen	$Glucose + Alk. Ferricyanide Yellow\longrightarrow Ferrocyanide$	Colorless end product; other reducing substances interfere with reaction
B. Condensation
Ortho-toluidine Method	Utilizes aromatic amines and hot acetic acid Forms Glycosylamine and Schiff's base which is emerald green in color This is the most specific method, but the reagent used is toxic
Anthrone (Phenols) Method	Forms hydroxymethyl furfural in hot acetic acid
II. ENZYMATIC METHODS
A. Glucose Oxidase
$Glucose + O^{2}\xrightarrow[Oxidation] {glucose oxidase}Cuprous Oxide$
Saifer Gernstenfield Method	$H_{2}O_2 + O-dianisidine\xrightarrow[Oxidation] {peroxidase} H_2O + oxidized chromogen$	Inhibited by reducing substances like BUA, Bilirubin, Glutathione, Ascorbic Acid
Trinder Method	uses 4-aminophenazone oxidatively coupled with Phenol Subject to less interference by increases serum levels of Creatinine, Uric Acid or Hemoglobin Inhibited by Catalase
Kodak Ektachem	A Dry Chemistry Method Uses Reflectance Spectrophotometry to measure the intensity of color through a lower transparent film
Glucometer	Home monitoring blood glucose assay method Uses a strip impregnated with a Glucose Oxidase reagent
B. Hexokinase
$\begin{alignat}{2} & Glucose + ATP\xrightarrow[Phosphorylation] {Hexokinase + Mg^{++}} G-6PO_4 + ADP \\ & G-6PO_4 + NADP\xrightarrow[Oxidation] {G-6PD} G-Phosphogluconate + NADPH + H^{+} \\ \end{alignat}$
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

[edit] 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 (HbA_1C)
Self-monitoring of Glucose level via Home Kits

[edit] 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.

**Causes of Abnormal Glucose Levels**
Persistent Hyperglycemia	Transient Hyperglycemia	Persistent Hypoglycemia	Transient Hypoglycemia
Reference Range, FBG: 70-110 mg/dl
Diabetes Mellitus	Pheochromocytoma	Insulinoma	Acute Alcohol Ingestion
Adrenal cortical hyperactivity Cushing's Syndrome	Severe Liver Disease	Adrenal cortical insufficiency Addison's Disease	Drugs: salicylates, antituberculosis agents
Hyperthyroidism	Acute stress reaction	Hypopituitarism	Severe Liver disease
Acromegaly	Shock	Galactosemia	Several Glycogen storage diseases
Obesity	Convulsions	Ectopic Insulin production from tumors	Hereditary fructose intolerance

[edit] 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.

[edit] 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:

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 is 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.

[edit] Converting glucose units

The U.S. uses mg/dL. The rest of the world, including Canada and Mexico, uses what is referred to as the "World Standard" of mmol/L.^{[citation needed]}

To convert blood glucose readings:

Divide the mg/dL figure by 18 (or multiply by 0.055) to get mmol/L.
Multiply the mmol/L figure by 18 (or divide by 0.055) to get mg/dL.

[edit] References

John Bernard Henry, M.D.: Clinical diagnosis and Management by Laboratory Methods 20th edition, Saunders, Philadelphia, PA, 2001.
Ronald A. Sacher and Richard A. McPherson: Widmann's Clinical Interpretation of Laboratory Tests 11th edition, F.A. Davis Company, 2001.

[edit] See also

Current research - Boronic acids in supramolecular chemistry: Saccharide recognition

Categories: Blood tests | Diabetes