((Short description|Concentration of glucose present in the blood (Glycaemia)))
((pp-semi-indef))
((Use dmy dates|date=November 2017))
[[File:Suckale08 fig3 glucose insulin day.png|thumbnail|300px|The fluctuation of blood sugar (red) and the sugar-lowering hormone
[[insulin]] (blue) in humans during the course of a day with three meals. One of the effects of a [[sucrose|sugar]]-rich vs a [[starch]]-rich meal is highlighted.<ref>((cite journal | vauthors = Daly ME, Vale C, Walker M, Littlefield A, Alberti KG, Mathers JC | title = Acute effects on insulin sensitivity and diurnal metabolic profiles of a high-sucrose compared with a high-starch diet | journal = The American Journal of Clinical Nutrition | volume = 67 | issue = 6 | pages = 1186–96 | date = June 1998 | pmid = 9625092 | doi = 10.1093/ajcn/67.6.1186 | url = http://www.ajcn.org/content/67/6/1186.full.pdf | doi-access = free ))</ref>]]

The '''blood sugar level''', '''blood sugar concentration''',  '''blood glucose level''', or '''glycemia''' is the measure of [[glucose]] concentrated in the [[blood]]. The body tightly [[blood sugar regulation|regulates blood glucose levels]] as a part of metabolic [[homeostasis]].<ref name="Glucose-Glycogen storage review" />

For a 70&nbsp;kg (154&nbsp;lb) human, approximately four grams of [[aqueous solution|dissolved]] glucose (also called "blood glucose") is maintained in the [[blood plasma]] at all times.<ref name="Glucose-Glycogen storage review">((cite journal | vauthors = Wasserman DH | title = Four grams of glucose | journal = American Journal of Physiology. Endocrinology and Metabolism | volume = 296 | issue = 1 | pages = E11–21 | date = January 2009 | pmid = 18840763 | pmc = 2636990 | doi = 10.1152/ajpendo.90563.2008 ))</ref> Glucose that is not circulating in the blood is stored in [[skeletal muscle]] and [[liver]] cells in the form of [[glycogen]];<ref name="Glucose-Glycogen storage review" /> 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.<ref name="Glucose-Glycogen storage review" /> Glucose can be transported from the intestines or liver to other tissues in the body via the bloodstream.<ref name="Glucose-Glycogen storage review" /> Cellular glucose uptake is primarily regulated<!--ref for additional uptake regulatory mechanisms: <ref name="Glucose-Glycogen storage review" />--> by [[insulin]], a [[hormone]] produced in the [[pancreas]].<ref name="Glucose-Glycogen storage review" /> 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.<ref name="Glucose-Glycogen storage review" /> A persistent elevation in blood glucose leads to glucose toxicity, which contributes to cell dysfunction and the pathology grouped together as complications of [[diabetes]].<ref name="Glucose-Glycogen storage review" />

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 [[millimolar|millimoles]].

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. There are different methods of [[glucose test|testing]] and measuring blood sugar levels.

Drinking [[Alcohol (drug)|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.<ref>Walker, Rosemary and Rodgers, Jill (2006) ''Type 2 Diabetes – Your Questions Answered''. Dorling Kindersley. ((ISBN|1-74033-550-3)).</ref>

==Units==
There are two ways of measuring blood glucose levels: In the United Kingdom and Commonwealth countries (Australia, Canada, India, etc.) and ex-USSR countries [[molar concentration]], measured in [[mmol/L]] (millimoles per litre, or millimolar, abbreviated mM). In the United States, Germany, Japan and many other countries [[mass concentration (chemistry)|mass concentration]] is measured in mg/dl (milligrams per [[deci-|deci]]litre).<ref>((Cite web|url=http://www.abbottdiabetescare.com.au/diabetes-faq-measure-units.php|title=Blood Glucose Monitor and Blood Glucose Meter - Blood Glucose Measurement Units FAQ|date=6 July 2011|archive-url=https://web.archive.org/web/20110706100159/http://www.abbottdiabetescare.com.au/diabetes-faq-measure-units.php|archive-date=6 July 2011))</ref>

Since the [[molecular mass]] of glucose C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> is approximately 180 g/mol, the difference between the two units is a factor of about 18, so 1&nbsp;mmol/L of glucose is equivalent to 18&nbsp;mg/dL.<ref name=convert/>((BSN|date=January 2024))

==Normal value range==

===Humans===
Normal blood glucose level (tested while fasting) for non-diabetics should be 3.9 - 5.5 mmol/L (70 -100 mg/dL).<ref name=":0">((cite web |last1=Davidson |first1=Nancy Klobassa |last2=Moreland |first2=Peggy |name-list-style=vanc |date=26 July 2011 |title=Living with diabetes blog |url=http://www.mayoclinic.com/health/blood-glucose-target-range/MY00494 |archive-url=https://web.archive.org/web/20130514173830/http://www.mayoclinic.com/health/blood-glucose-target-range/MY00494 |archive-date=14 May 2013 |work=Mayo Clinic))</ref><ref name=":1">((cite web |last1=Schuster |first1=Dara |name-list-style=vanc |date=14 August 2008 |title=What Does 'Post-Meal (Or Post-Prandial) Blood Sugar' Mean And What Does It Tell You? |url=https://abcnews.go.com/Health/DiabetesScreening/story?id=3812972 |work=Ohio State University))</ref><ref>((Cite web |title=Indicator Metadata Registry Details |url=https://www.who.int/data/gho/indicator-metadata-registry/imr-details/2380 |access-date=2024-03-15 |website=www.who.int |language=en |postscript=. Converted 100 mg/dL to approximately 5.5 mmol/L using the conversion factor 18.02 g/mol, rather than the 5.6 mmol/L value stated by the WHO.))</ref>

According to the [[American Diabetes Association]], the fasting blood glucose target range for diabetics, should be 3.9 - 7.2 mmol/L (70 - 130 mg/dL) and less than 10&nbsp;mmol/L (180&nbsp;mg/dL)  two hours after meals (as measured by a blood glucose monitor).<ref name=":0" /><ref name=":1" /><ref>((cite journal |author=American Diabetes Association |date=January 2006 |title=Standards of medical care in diabetes--2006 |url=http://care.diabetesjournals.org/content/29/suppl_1/s4.full |journal=Diabetes Care |volume=29 Suppl 1 |issue=Supplement 1 |pages=S4–42 |doi=10.2337/diacare.29.s1.06.s4 |pmid=16373931 |s2cid=29740430 |quote=Standards of Medical Care – Table 6 and Table 7, Correlation between A1C level and Mean Plasma Glucose Levels on Multiple Testing over 2–3 months |doi-access=free))</ref>

[[Reference ranges for blood tests#Other electrolytes and metabolites|Normal value ranges]] may vary slightly between laboratories. [[Blood sugar regulation|Glucose homeostasis]], when operating normally, restores the blood sugar level to a narrow range of about 4.4 to 6.1&nbsp;mmol/L (79 to 110&nbsp;mg/dL) (as measured by a [[Glucose test#Reference ranges|fasting blood glucose test]]).<ref>((cite journal |year=2000 |title=Screening for Type 2 Diabetes |url=http://journal.diabetes.org/clinicaldiabetes/v18n22000/pg69.htm |journal=Clinical Diabetes |volume=18 |issue=2))</ref>

The global mean fasting plasma blood glucose level in humans is about 5.5&nbsp;mmol/L (100&nbsp;mg/dL);<ref>((cite journal |last1=Danaei |first1=G |s2cid=13951614 |title=National, regional, and global trends in fasting plasma glucose and diabetes prevalence since 1980: systematic analysis of health examination surveys and epidemiological studies with 370 country-years and 2·7 million participants. |journal=The Lancet |date=2 July 2011 |volume=378 |issue=9785 |pages=31–40 |doi=10.1016/S0140-6736(11)60679-X |pmid=21705069 ))</ref><ref name="convert">[http://www.faqs.org/faqs/diabetes/faq/part1/section-9.html What are mg/dL and mmol/L? How to convert? Glucose? Cholesterol?] Advameg, Inc.</ref> however, this level fluctuates throughout the day. Blood sugar levels for those without diabetes and who are not fasting should be below 6.9&nbsp;mmol/L (125&nbsp;mg/dL).<ref>((Cite web |title=Blood sugar test: MedlinePlus Medical Encyclopedia |url=https://medlineplus.gov/ency/article/003482.htm |access-date=2024-03-15 |website=medlineplus.gov |language=en))</ref>

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&nbsp;mmol/L (140&nbsp;mg/dL) or slightly more. 

The actual amount of glucose in the blood and body fluids is very small. In a healthy adult male of ((Convert|75|kg|lb|abbr=on)) with a blood volume of 5&nbsp;L, a blood glucose level of 5.5&nbsp;mmol/L (100&nbsp;mg/dL) amounts to 5&nbsp;g, equivalent to about a teaspoonful of sugar.<ref>USDA National Nutrient Database for Standard Reference, Release 22 (2009)</ref> Part of the reason why this amount is so small is that, to maintain an influx of glucose into cells, [[enzyme]]s modify glucose by adding [[phosphate]] or other groups to it.((citation needed|date=April 2022))

===Other animals===

In general, ranges of blood sugar in common domestic [[Ruminantia|ruminants]] are lower than in many [[monogastric]] mammals.<ref>((cite book | vauthors = Eiler H |year=2004 |chapter=Endocrine glands |pages=[https://archive.org/details/dukesphysiologyo0012duke/page/621 621]–69 | veditors = Reese WO |title=Dukes' Physiology of Domestic Animals | url = https://archive.org/details/dukesphysiologyo0012duke | url-access = registration |edition=12th |location=Ithaca, NY |publisher=Comstock |isbn=978-0801442384 ))</ref>   However this generalization does not extend to wild ruminants or [[camelid]]s.  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.<ref>((cite book |veditors = Kahn CM |year=2005 |title=Merck Veterinary Manual |url = https://archive.org/details/merckveterinarym09edunse |url-access = registration |edition=9th |publisher=Merck & Co. |location=Whitehouse Station |isbn=978-0911910506 ))</ref>  A 90 percent reference interval for serum glucose of 26 to 181&nbsp;mg/dL has been reported for captured mountain goats (''[[Oreamnos americanus]]''), where no effects of the pursuit and capture on measured levels were evident.<ref>((cite journal|author1=Rice, C. G.  |author2=Hall, B. |s2cid=56564674 |title= Hematologic and biochemical reference intervals for mountain goats (''Oreamnos americanus''): effects of capture conditions|doi=10.3955/0029-344X-81.3.206|year=2007|journal=Northwest Science|volume=81|issue=3|pages=206))</ref>  For beluga whales, the 25–75 percent range for serum glucose has been estimated to be 94 to 115&nbsp;mg/dL.<ref>((cite journal | vauthors = Cornell LH, Duffield DS, Joseph BE, Stark B | title = Hematology and serum chemistry values in the beluga (Delphinapterus leucas) | journal = Journal of Wildlife Diseases | volume = 24 | issue = 2 | pages = 220–4 | date = April 1988 | pmid = 3373628 | doi = 10.7589/0090-3558-24.2.220 | doi-access = free ))</ref>  For the white rhinoceros, one study has indicated that the 95 percent range is 28 to 140&nbsp;mg/dL.<ref>((cite journal|url=http://www.rhinoresourcecenter.com/pdf_files/123/1239956678.pdf|title=Baseline Laboratory Data for the White Rhinoceros (''Ceratotherium simum simum'')|author=Seal, U. S. |author2=Barton, R. |author3=Mather, L. |author4=Gray, C. W. |pages=11–17|journal=The Journal of Zoo Animal Medicine|volume=7|issue=1 |year=1976|jstor=20094341))</ref>  For harp seals, a serum glucose range of 4.9 to 12.1&nbsp;mmol/L [i.e. 88 to 218&nbsp;mg/dL] has been reported; for hooded seals, a range of 7.5 to 15.7&nbsp;mmol/L [i.e. about 135 to 283&nbsp;mg/dL] has been reported.<ref>((cite journal | vauthors = Boily F, Beaudoin S, Measures LN | s2cid = 21875860 | title = Hematology and serum chemistry of harp (Phoca groenlandica) and hooded seals (Cystophora cristata) during the breeding season, in the Gulf of St. Lawrence, Canada | journal = Journal of Wildlife Diseases | volume = 42 | issue = 1 | pages = 115–32 | date = January 2006 | pmid = 16699154 | doi = 10.7589/0090-3558-42.1.115 | doi-access = free ))</ref>

==Regulation==<!--Blood sugar regulation redirects here-->
((Main|Blood sugar regulation))

The body's [[homeostasis|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.<ref>((Citation |last1=Felig |first1=PHILIP |title=Hormonal Interactions in the Regulation of Blood Glucose |date=1979-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780125711357500163 |work=Proceedings of the 1978 Laurentian Hormone Conference |volume=35 |pages=501–532 |editor-last=Greep |editor-first=ROY O. |access-date=2023-04-09 |series=Recent Progress in Hormone Research |place=Boston |publisher=Academic Press |language=en |isbn=978-0-12-571135-7 |last2=Sherwin |first2=ROBERT S. |last3=Soman |first3=VIJAY |last4=Wahren |first4=JOHN |last5=Hendler |first5=ROSA |last6=Sacca |first6=LUIGI |last7=Eigler |first7=NEIL |last8=Goldberg |first8=DAVID |last9=Walesky |first9=MARY))</ref>

There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels:
* [[catabolic]] hormones (such as [[glucagon]], [[cortisol]] and [[catecholamines]]) which increase blood glucose;<ref>((cite book|last1=Lehninger|first1=Albert|last2=Nelson|first2=David|last3=Cox|first3=Michael | name-list-style = vanc |title=Lehininger Principles of Biochemistry|date=2017|publisher=W.H. Freedom|location=New York|isbn=9781319117689|page=934))</ref>
* and one [[anabolic]] hormone ([[insulin]]), which decreases blood glucose.

These hormones are secreted from [[pancreatic islets]] (bundles of endocrine tissues), of which there are four types: alpha (A) cells, beta (B) cells, Delta (D) cells and F cells. Glucagon is secreted from alpha cells, while insulin is secreted by beta cells. Together they regulate the blood-glucose levels through negative feedback, a process where the end product of one reaction stimulates the beginning of another reaction. In blood-glucose levels, insulin lowers the concentration of glucose in the blood. The lower blood-glucose level (a product of the insulin secretion) triggers glucagon to be secreted, and repeats the cycle.<ref>((cite book|last1=Tortora|first1=Gerard | name-list-style = vanc |title=Principles Anatomy and Physiology|date=December 2016|publisher=John Wiley & Sons, Inc.|location=New York|isbn=9781119343738|pages=Chapter 18|edition=15))</ref>

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.<ref>((cite book|last1=Lehninger|first1=Albert|last2=Nelson|first2=David|last3=Cox|first3=Michael| name-list-style = vanc |title=Lehninger Principles of Biochemistry|date=2017|publisher=W.H.Freeman|location=New York|isbn=9781319117689|page=930|edition=7th))</ref>

==Abnormalities==
((See also|Dysglycemia))

===High blood sugar===
((main|Hyperglycemia))

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,<ref>((Cite news|url=https://www.sciencedaily.com/releases/2013/02/130201100149.htm|title=Excess sugar linked to cancer|work=Science Daily|language=en))</ref> eye, kidney, and nerve damage.<ref>((Cite news|url=https://www.mayoclinic.org/diseases-conditions/diabetic-ketoacidosis/symptoms-causes/syc-20371551|title=Diabetic ketoacidosis - Symptoms and causes|work=Mayo Clinic|access-date=2018-01-30|language=en))</ref>

Blood sugar levels above 16.7((nbsp))mmol/L (300((nbsp))mg/dL) can cause fatal reactions. Ketones will be very high (a magnitude higher than when eating a very low carbohydrate diet) initiating [[ketoacidosis]]. The ADA (American Diabetes Association) recommends seeing a doctor if blood glucose reaches 13.3 mmol/L (240 mg/dL),<ref>((Cite web |date=2019-03-28 |title=Diabetic emergencies: Warning signs and what to do |url=https://www.medicalnewstoday.com/articles/317436 |access-date=2024-01-23 |website=www.medicalnewstoday.com |language=en))</ref> and it is recommended to seek emergency treatment at 15((nbsp))mmol/L (270((nbsp))mg/dL) blood glucose if Ketones are present.<ref>((Cite web |last=Australia |first=Healthdirect |date=2023-11-28 |title=Hyperglycaemia (high blood sugar) |url=https://www.healthdirect.gov.au/hyperglycaemia-high-blood-sugar |access-date=2024-01-23 |website=www.healthdirect.gov.au |language=en-AU))</ref> 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.<ref name="BBDdiabetesM2">((Cite journal|author1 = Consumer Reports Health Best Buy Drugs |author1-link = Consumer Reports|title = The Oral Diabetes Drugs: Treating Type 2 Diabetes |journal = Best Buy Drugs |page =2 |url = http://www.consumerreports.org/health/resources/pdf/best-buy-drugs/DiabetesUpdate-FINAL-Feb09.pdf |access-date = 18 September 2012))</ref> Diet changes and exercise implementation may also be part of a treatment plan for diabetes.<ref>((Cite journal |last=Fowler |first=Michael J. |date=2007-06-22 |title=Diet and exercise. |url=https://go.gale.com/ps/i.do?p=AONE&sw=w&issn=08918929&v=2.1&it=r&id=GALE%7CA167029985&sid=googleScholar&linkaccess=abs |journal=Clinical Diabetes |language=English |volume=25 |issue=3 |pages=105–110|doi=10.2337/diaclin.25.3.105 ))</ref>

Some medications may cause a rise in blood sugars of diabetics, such as steroid medications, including cortisone, hydrocortisone, prednisolone, prednisone, and dexamethasone.<ref>((Cite web|url=https://www.ndss.com.au/about-diabetes/resources/find-a-resource/steroid-medications-and-diabetes-fact-sheet/|title=Steroid medications and diabetes fact sheet – NDSS|website=www.ndss.com.au))</ref>

===Low blood sugar===
((main|Hypoglycemia))
When the blood sugar level is below 70&nbsp;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.<ref>((cite news |title=Low blood sugar - self-care: MedlinePlus Medical Encyclopedia |url=https://medlineplus.gov/ency/patientinstructions/000085.htm |work=medlineplus.gov |language=en))</ref> 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; [[Unconsciousness|loss of consciousness]].((citation needed|date=April 2022))

Mechanisms that restore satisfactory blood glucose levels after extreme [[hypoglycemia]] (below 2.2&nbsp;mmol/L or 40&nbsp;mg/dL) must be quick and effective to prevent extremely serious consequences of insufficient glucose: confusion or unsteadiness and, in the extreme (below 0.8&nbsp;mmol/L or 15&nbsp;mg/dL)  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 (diabetes or pre-diabetes, obesity or overweight, [[hyperlipidemia]], [[hypertension]], etc.), 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 (the liver and brain are examples). Symptomatic hypoglycemia is most likely associated with [[diabetes]] and [[liver disease]] (especially overnight or postprandial), 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.((cn|date=January 2024))

==Glucose measurement==
((Further| Blood glucose monitoring|Continuous glucose monitor|Glucose meter))
In the past to measure blood glucose it was necessary to take a blood sample, as explained below, but since 2015 it has also been possible to use a [[continuous glucose monitor]], which involves an electrode placed under the skin. Both methods, as of 2023, cost hundreds of dollars or euros per year for supplies needed.((cn|date=January 2024))

===Sample source===
[[Glucose test]]ing in a fasting individual shows comparable levels of glucose in arterial, venous, and capillary blood. But following meals, capillary and arterial blood glucose levels can be significantly higher than venous levels. Although these differences vary widely, one study found that following the consumption of 50 grams of glucose, "the mean capillary blood glucose concentration is higher than the mean venous blood glucose concentration by 35%."<ref>((cite journal | vauthors = Somogyi M | title = Studies of arteriovenous differences in blood sugar; effect of alimentary hyperglycemia on the rate of extrahepatic glucose assimilation | journal = The Journal of Biological Chemistry | volume = 174 | issue = 1 | pages = 189–200 | date = May 1948 | doi = 10.1016/S0021-9258(18)57386-5 | pmid = 18914074 | url = http://www.jbc.org/content/174/1/189.full.pdf | doi-access = free ))</ref><ref>((cite web | last = Roe | first = Jeffrey | name-list-style = vanc | url = http://www.bestthinking.com/articles/medicine/internal_medicine/hematology/glucose-concentration-difference-between-arterial-capillary-and-venous-blood | archive-url = https://web.archive.org/web/20141204114840/http://www.bestthinking.com/articles/medicine/internal_medicine/hematology/glucose-concentration-difference-between-arterial-capillary-and-venous-blood | archive-date = 4 December 2014 | url-status = dead | title = Glucose Concentration Difference Between Arterial, Capillary, and Venous Blood | work = Best Thinking ))</ref>

===Sample type===
Glucose is measured in whole blood, [[blood plasma|plasma]] or [[blood serum|serum]]. Historically, blood glucose values were given in terms of whole blood, but most laboratories now measure and report plasma or serum glucose levels. Because [[red blood cell]]s (erythrocytes) have a higher concentration of protein (e.g., hemoglobin) than serum, serum has a higher water content and consequently more dissolved glucose than does whole blood. To convert from whole-blood glucose, multiplication by 1.14<ref name="ReferenceA">((cite book|last1=Cox|first1=David L | last2 = Nelson | first2 = Michael M.| name-list-style = vanc |title=Lehninger principles of biochemistry|date=2013|publisher=W.H. Freeman|location=New York|isbn=9781429234146|pages=950|edition=6th))</ref> has been shown to generally give the serum/plasma level.

To prevent contamination of the sample with [[intravenous fluids]], particular care should be given to drawing blood samples from the arm opposite the one in which an intravenous line is inserted. Alternatively, blood can be drawn from the same arm with an IV line after the IV has been turned off for at least 5 minutes, and the arm has been elevated to drain infused fluids away from the vein. Inattention can lead to large errors, since as little as 10% contamination with a 5% [[glucose]] solution (D5W) will elevate glucose in a sample by 500&nbsp;mg/dL or more. The actual concentration of glucose in blood is very low, even in the hyperglycemic.((citation needed|date=November 2021))

===Measurement techniques===
((More citations needed section|date=December 2016))
Two major methods have been used to measure glucose. The first, still in use in some places, is a chemical method exploiting the nonspecific reducing property of glucose in a reaction with an indicator substance that changes color when reduced. Since other blood compounds also have reducing properties (e.g., urea, which can be abnormally high in uremic patients), this technique can produce erroneous readings in some situations (5–15&nbsp;mg/dL has been reported). The more recent technique, using enzymes specific to glucose, is less susceptible to this kind of error. The two most common employed enzymes are glucose oxidase and hexokinase.<ref name="W.H. Freeman">((cite book|last1=Cox|first1=Michael M.|last2=Lehninger|first2=Albert L.|last3=Nelson|first3=David L.| name-list-style = vanc |title=Lehninger Principles of Biochemistry|date=2017|publisher=W.H. Freeman|location=New York|isbn=9781319117689|pages=248–49))</ref> Average blood glucose concentrations can also be measured. This method measures the level of [[glycated hemoglobin]], which is representative of the average blood glucose levels over the last, approximately, 120 days.<ref name="W.H. Freeman"/>

In either case, the chemical system is commonly contained on a test strip which is inserted into a meter, and then has a blood sample applied. Test-strip shapes and their exact chemical composition vary between meter systems and cannot be interchanged. Formerly, some test strips were read (after timing and wiping away the blood sample) by visual comparison against a color chart printed on the vial label. Strips of this type are still used for urine glucose readings, but for blood glucose levels they are obsolete. Their error rates were, in any case, much higher. Errors when using test strips were often caused by the age of the strip or exposure to high temperatures or humidity.<ref>((cite journal | vauthors = Ginsberg BH | title = Factors affecting blood glucose monitoring: sources of errors in measurement | journal = Journal of Diabetes Science and Technology | volume = 3 | issue = 4 | pages = 903–13 | date = July 2009 | pmid = 20144340 | pmc = 2769960 | doi = 10.1177/193229680900300438 ))</ref> More precise blood glucose measurements are performed in a [[medical laboratory]], using hexokinase, glucose oxidase, or glucose dehydrogenase enzymes.

[[Urine glucose]] readings, however taken, are much less useful. In properly functioning kidneys, glucose does not appear in urine until the [[renal threshold]] for glucose has been exceeded. This is substantially above any normal glucose level, and is evidence of an existing severe hyperglycemic condition. However, as urine is stored in the bladder, any glucose in it might have been produced at any time since the last time the bladder was emptied. Since metabolic conditions change rapidly, as a result of any of several factors, this is delayed news and gives no warning of a developing condition.<ref>((Cite journal |last1=Singer |first1=D. E. |last2=Coley |first2=C. M. |last3=Samet |first3=J. H. |last4=Nathan |first4=D. M. |date=1989-01-15 |title=Tests of glycemia in diabetes mellitus. Their use in establishing a diagnosis and in treatment |url=https://pubmed.ncbi.nlm.nih.gov/2642375 |journal=Annals of Internal Medicine |volume=110 |issue=2 |pages=125–137 |doi=10.7326/0003-4819-110-2-125 |issn=0003-4819 |pmid=2642375))</ref> Blood glucose monitoring is far preferable, both clinically and for home monitoring by patients. Healthy urine glucose levels were first standardized and published in 1965<ref>((cite journal | vauthors = Renschler HE, Weicker H, von Baeyer H | title = [The upper limit of glucose concentration in the urine of healthy subjects] | journal = Deutsche Medizinische Wochenschrift | volume = 90 | issue = 53 | pages = 2349–53 | date = December 1965 | pmid = 5851934 ))</ref> by [[Hans Renschler]].

A noninvasive method of sampling to monitor glucose levels has emerged using an ''exhaled breath condensate''. However this method does need highly sensitive glucose biosensors.<ref name="Tankasala">((cite journal |last1=Tankasala |first1=D |last2=Linnes |first2=JC |title=Noninvasive glucose detection in exhaled breath condensate. |journal=Translational Research |date=November 2019 |volume=213 |pages=1–22 |doi=10.1016/j.trsl.2019.05.006 |pmid=31194942|pmc=6783357 ))</ref>

{| class="wikitable" style="text-align:center;"
|-
! colspan="3" style="background:orange; color:black;" | I. Chemical methods
|-
! colspan="3" style="background:lightblue; color:black;" | A. Oxidation-reduction reaction
|-
| colspan="3" style="background-color:white; color:black;" | <math>\mathrm{Glucose} + \mathrm{Alkaline\ copper\ tartarate}\xrightarrow{\mathrm{Reduction)) \mathrm{Cuprous\ oxide} </math>
|-
! width="900pt" colspan="3" | 1. Alkaline copper reduction
|-
| Folin-Wu method
| style="background-color:white; color:black;" | <math>\mathrm{Cu}^{2+} + \mathrm{Phosphomolybdic\ acid}\xrightarrow{\mathrm{Oxidation)) \mathrm{Phosphomolybdenum\ oxide}</math>
| Blue end-product
|-
| Benedict's method
| colspan="2" style="background-color:white; color:black;" |
* Modification of Folin–Wu method for qualitative urine glucose.
|-
| Nelson–Somogyi method
| style="background-color:white; color:black;" | <math>\mathrm{Cu}^{2+} + \mathrm{Arsenomolybdic\ acid}\xrightarrow{\mathrm{Oxidation)) \mathrm{Arsenomolybdenum\ oxide}</math>
| Blue end-product.
|-
| Neocuproine method
| style="background-color:white; color:black;" | <math>\mathrm{Cu}^{2+} + \mathrm{Neocuproine}\xrightarrow{\mathrm{Oxidation)) \mathrm{Cu}^{2+} \mathrm{neocuproine\ complex} </math>*
| Yellow-orange color neocuproine<ref>((cite web |url=http://hazard.com/msds/mf/baker/baker/files/d6824.htm |title=Neocuproine MSDS |website=hazard.com |url-status=usurped |archive-url=https://archive.today/20120710090826/http://hazard.com/msds/mf/baker/baker/files/d6824.htm |archive-date=2012-07-10 ))</ref>
|-
| Shaeffer–Hartmann–Somogyi
| style="background-color:white; color:black;" |
* Uses the principle of [[iodine]] reaction with cuprous byproduct.
* Excess I<sub>2</sub> is then titrated with [[thiosulfate]].
|-
! colspan="3" | 2. Alkaline Ferricyanide reduction
|-
| Hagedorn–Jensen
| style="background-color:white; color:black;" | <math>\mathrm{Glucose} + \mathrm{Alkaline\ ferricyanide}\longrightarrow \mathrm{Ferrocyanide}</math>
| Colorless end product; other reducing substances interfere with reaction.
|-
| colspan="3" style="background:lightblue; color:black;" | B. Condensation
|-
| Ortho-toluidine method
| colspan="2" style="background-color:white; color:black;" |
* Uses [[aromatic amine]]s 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
| colspan="2" style="background-color:white; color:black;" |
* Forms hydroxymethyl furfural in hot acetic acid
|-
! colspan="3" style="background:orange; color:black;" | II. Enzymatic methods
|-
! colspan="3" style="background:lightblue; color:black;" | A. Glucose oxidase
|-
| colspan="3" style="background-color:white; color:black;" |<math>\mathrm{Glucose} + \mathrm{O}_{2}\xrightarrow[\mathrm{Oxidation}] {\mathrm{glucose\ oxidase))\textrm{D-glucono-1,5-lactone} + \mathrm{H_{2}O_{2)) </math>
|-
| Saifer–Gerstenfeld method
| style="background-color:white; color:black;" | <math>\mathrm{H_{2}O_2} + \textit{O}\text{-dianisidine}\xrightarrow[\mathrm{Oxidation}] {\mathrm{peroxidase)) \mathrm{H_2O} + \mathrm{oxidized\ chromogen}</math>
| Inhibited by reducing substances like BUA, [[bilirubin]], [[glutathione]], [[ascorbic acid]].
|-
| Trinder method
| colspan="2" style="background-color:white; color:black;" |
* Uses [https://web.archive.org/web/20061214205244/http://www.online-medical-dictionary.org/4-Aminophenazone.asp?q=4-Aminophenazone 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
| colspan="2" style="background-color:white; color:black;" |
* A dry chemistry method.
* Uses [[spectrophotometry]] to measure the intensity of color through a lower transparent film.
|-
| Glucometer
| colspan="2" style="background-color:white; color:black;" |
* Home monitoring blood glucose assay method.
* Uses a strip impregnated with a glucose oxidase reagent.
|-
! colspan="3" style="background:lightblue; color:black;" | B. Hexokinase
|-
| colspan="3" style="background-color:white; color:black;" |
<math>\begin{alignat}{2}
  & \mathrm{Glucose} + \mathrm{ATP}\xrightarrow[\mathrm{Phosphorylation}] {\mathrm{Hexokinase} + \mathrm{Mg}^{2+)) \textrm{G-6PO}_4 + \mathrm{ADP} \\
  & \textrm{G-6PO}_4 + \mathrm{NADP}\xrightarrow[\mathrm{Oxidation}] {\textrm{G-6PD)) \textrm{6-Phosphogluconate} + \mathrm{NADPH} + \mathrm{H}^{+} \\
\end{alignat}</math>
|-
| colspan="3" style="background-color:white; color:black;" |
* [[NADP]] as cofactor.
* NADPH (reduced product) is measured in 340&nbsp;nm.
* More specific than glucose oxidase method due to G-6PO<sub>4</sub>, which inhibits interfering substances except when sample is hemolyzed.
|}

===Clinical correlation===
The fasting blood glucose level, which is measured after a fast of 8 hours, is the most commonly used indication of overall glucose homeostasis, largely because disturbing events such as food intake are avoided. Conditions affecting glucose levels are shown in the table below. Abnormalities in these test results are due to problems in the multiple control mechanism of glucose regulation.((citation needed|date=November 2021))

The metabolic response to a carbohydrate challenge is conveniently assessed by a postprandial glucose level drawn 2 hours after a meal or a glucose load. In addition, the glucose tolerance test, consisting of several timed measurements after a standardized amount of oral glucose intake, is used to aid in the diagnosis of [[diabetes]].((cn|date=January 2024))

Error rates for blood glucose measurements systems vary, depending on laboratories, and on the methods used. Colorimetry techniques can be biased by color changes in test strips (from airborne or finger-borne contamination, perhaps) or interference (e.g., tinting contaminants) with light source or the light sensor. Electrical techniques are less susceptible to these errors, though not to others. In home use, the most important issue is not accuracy, but trend. Thus if a meter / test strip system is consistently wrong by 10%, there will be little consequence, as long as changes (e.g., due to exercise or medication adjustments) are properly tracked. In the US, home use blood test meters must be approved by the federal [[Food and Drug Administration]] before they can be sold.((cn|date=January 2024))

Finally, there are several influences on blood glucose level aside from food intake. Infection, for instance, tends to change blood glucose levels, as does stress either physical or psychological. Exercise, especially if prolonged or long after the most recent meal, will have an effect as well. In the typical person, maintenance of blood glucose at near constant levels will nevertheless be quite effective.((Clarify|date=August 2010))
{| class="wikitable" style="text-align:center"
|+ '''Causes of abnormal glucose levels'''
! style="background:#ffdfae;" | Persistent hyperglycemia
! style="background:#ffdfae;" | Transient hyperglycemia
! style="background:#ffdfae;" | Persistent hypoglycemia
! style="background:#ffdfae;" | Transient hypoglycemia
|-
| colspan="4" style="background-color:lightblue; color:black;" | Reference range, [[fasting blood glucose]] (FBG): 70–110&nbsp;mg/dL
|-
| [[Diabetes]] mellitus
| [[Pheochromocytoma]]
| [[Insulinoma]]
| Acute [[alcohol intoxication]] or ingestion
|-
| Adrenal cortical hyperactivity [[Cushing's syndrome]]
| Severe [[liver disease]]
| Adrenal cortical insufficiency [[Addison's disease]]
| Drugs: [[salicylates]], antituberculosis agents
|-
| [[Hyperthyroidism]]
| [[Stress hyperglycemia|Acute stress reaction]]
| [[Hypopituitarism]]
| Severe [[liver disease]]
|-
| [[Acromegaly]]
| [[Shock (circulatory)|Shock]]
| [[Galactosemia]]
| Several [[glycogen storage diseases]]
|-
| [[Obesity]]
| [[Convulsions]]
| [[Ectopic hormone]] production from tumors
| [[Hereditary fructose intolerance]]
|}

== See also ==
* [[Blood glucose monitoring]]
* [[Glycemic index]]
* [[Boronic acid#Boronic acids in supramolecular chemistry|Saccharide recognition by boronic acids]]

== References ==
((Reflist))

== Further reading ==
* ((cite book |first=John Bernard |last=Henry | name-list-style = vanc |title=Clinical diagnosis and Management by Laboratory Methods |edition=20th |publisher=Saunders |location=Philadelphia |year=2001 |isbn=978-0721688640 ))
* ((cite journal | vauthors = Levine R | title = Monosaccharides in health and disease | journal = Annual Review of Nutrition | volume = 6 | pages = 211–24 | year = 1986 | pmid =  3524617| doi = 10.1146/annurev.nu.06.070186.001235 ))
* ((cite journal | vauthors = Röder PV, Wu B, Liu Y, Han W | title = Pancreatic regulation of glucose homeostasis | journal = Experimental & Molecular Medicine | volume = 48 | issue = 3, March | pages = e219 | date = March 2016 | pmid = 26964835 | pmc = 4892884 | doi = 10.1038/emm.2016.6 ))

==External links==
* ((Commons category-inline))
* [https://web.archive.org/web/20121113144108/http://www.acb.org.uk/docs/NHLM/Glucose.pdf Glucose (blood, serum, plasma): analyte monograph] – The Association for Clinical Biochemistry and Laboratory Medicine

((Disease of the pancreas and glucose metabolism))
((Blood tests))
((Authority control))

((DEFAULTSORT:Blood Sugar))
[[Category:Blood tests]]
[[Category:Concentration indicators]]
[[Category:Diabetes]]
[[Category:Diagnostic endocrinology]]
[[Category:Human homeostasis]]