Editing Glucose tolerance test (section)

==Testing==
Since the 1970s, the [[World Health Organization]] and other organizations interested in diabetes agreed on a standard dose and duration.<ref>{{Cite journal |title=Standards of Medical Care in Diabetes—2013 |journal=Diabetes Care |year=2013 |volume=36 |issue=Suppl 1 |pages=S11–S66 |doi=10.2337/dc13-S011 |issn=0149-5992 |pmc=3537269 |pmid=23264422|author1=American Diabetes Association }}</ref>

===Preparation===
The patient is instructed not to restrict [[carbohydrate]] intake in the days or weeks before the test.<ref>{{cite journal|doi=10.1210/jendso/bvab049|title=Carbohydrate Intake Prior to Oral Glucose Tolerance Testing |year=2021 |last1=Klein |first1=Klara R. |last2=Walker |first2=Christopher P. |last3=McFerren |first3=Amber L. |last4=Huffman |first4=Halie |last5=Frohlich |first5=Flavio |last6=Buse |first6=John B. |journal=Journal of the Endocrine Society |volume=5 |issue=5 |pages=bvab049 |pmid=33928207 |pmc=8059359 |doi-access=free }}</ref> The test should not be done during an illness, as results may not reflect the patient's glucose metabolism when healthy. A full adult dose should not be given to a person weighing less than 42.6&nbsp;kg (94&nbsp;lb), or the excessive glucose may produce a [[false positive]] result. Usually the OGTT is performed in the morning as glucose tolerance can exhibit a diurnal rhythm with a significant decrease in the afternoon. The patient is instructed to [[fasting|fast]] (water is allowed) for 8–12 hours prior to the tests. Medication such as large doses of [[salicylates]], [[diuretics]], [[anticonvulsants]], and [[oral contraceptives]] affect the glucose tolerance test.<ref>{{Cite journal |last1=Salvaggio |first1=Heather L |last2=Zaenglein |first2=Andrea L |date=2010-08-09 |title=Examining the use of oral contraceptives in the management of acne |journal=International Journal of Women's Health |volume=2 |pages=69–76 |doi=10.2147/ijwh.s5915 |issn=1179-1411 |pmc=2971728 |pmid=21072299 |doi-access=free }}</ref>

===Procedure===
# A zero time (baseline) blood sample is drawn.
# The patient is then given a measured dose (below) of glucose solution to drink within a 5-minute time frame.
# Blood is drawn at intervals for measurement of glucose ([[blood sugar]]), and sometimes [[insulin]] levels. The intervals and number of samples vary according to the purpose of the test. For simple diabetes screening, the most important sample is the 2 hour sample and the 0 and 2 hour samples may be the only ones collected. A laboratory may continue to collect blood for up to 6 hours depending on the protocol requested by the physician.

===Dose of glucose and variations===
* 75&nbsp;g of oral dose is the recommendation of the [[World Health Organization|WHO]] to be used in all adults,<ref name=who/> and is the main dosage used in the United States.<ref name=ADAstandards2020/> The dose is adjusted for weight only in children.<ref name=who>{{cite book|author=World Health Organization and International Diabetes Federation|title=Definition, diagnosis and classification of diabetes mellitus and its complications|location=Geneva, Switzerland|publisher=World Health Organization|year=1999}}</ref> The dose should be drunk within 5 minutes.
* A variant is often used in [[pregnancy]] to screen for [[gestational diabetes]], with a screening test of 50&nbsp;g over one hour. If elevated, this is followed with a test of 100&nbsp;g over three hours.<ref name=ADAstandards2020/>
* In UK general practice, the standard glucose load was provided by 394&nbsp;ml of the energy drink [[Lucozade]] with original carbonated flavour, but this is being superseded by purpose-made drinks.<ref>
{{cite web|url=http://www.salforddiabetescare.co.uk/index2.php?nav_id=443|title=Glucose Tolerance Tests in Primary Care|author=Salford Royal NHS Trust|access-date=2012-06-20}}</ref><ref>{{cite web|url=http://www.erypct.nhs.uk/upload/HERHIS/East%20Riding%20PCTs/Document%20Store/Policies/diabetes_OGT_protocol&guidance_final_apr09.pdf|title=Oral Glucose Tolerance Tests: Protocol and Guidance|author=Jane Patmore|year=2009|publisher=Hull and East Riding Diabetes Network, Hull NHS teaching hospitals trust|access-date=2012-06-20|archive-url=https://web.archive.org/web/20120506131302/http://www.erypct.nhs.uk/upload/HERHIS/East%20Riding%20PCTs/Document%20Store/Policies/diabetes_OGT_protocol%26guidance_final_apr09.pdf|archive-date=2012-05-06|url-status=dead}}</ref>

===Substances measured and variations===
If [[renal glycosuria]] (sugar excreted in the urine despite normal levels in the blood) is suspected, urine samples may also be collected for testing along with the fasting and 2 hour blood tests.<ref>{{Cite web |title=Glucose - Urine |url=https://www.ucsfhealth.org/Medical%20Tests/003581 |access-date=2022-10-17 |website=ucsfhealth.org |language=en}}</ref>