Glucose tolerance test

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Glucose tolerance test
Glucose metabolism.svg
A diagram of glucose metabolism
Purposedetermine how quickly glucose is cleared from blood

The glucose tolerance test (GTT, not to be confused with GGT test) is a medical test in which glucose is given and blood samples taken afterward to determine how quickly it is cleared from the blood. [1] The test is usually used to test for diabetes, insulin resistance, impaired beta cell function, [2] and sometimes reactive hypoglycemia and acromegaly, or rarer disorders of carbohydrate metabolism. In the most commonly performed version of the test, an oral glucose tolerance test (OGTT), a standard dose of glucose is ingested by mouth and blood levels are checked two hours later. [3] Many variations of the GTT have been devised over the years for various purposes, with different standard doses of glucose, different routes of administration, different intervals and durations of sampling, and various substances measured in addition to blood glucose.

Contents

History

The glucose tolerance test was first described in 1923 by Jerome W. Conn. [4]

The test was based on the previous work in 1913 by A. T. B. Jacobson in determining that carbohydrate ingestion results in blood glucose fluctuations, [5] and the premise (named the Staub-Traugott Phenomenon after its first observers H. Staub in 1921 and K. Traugott in 1922) that a normal patient fed glucose will rapidly return to normal levels of blood glucose after an initial spike, and will see improved reaction to subsequent glucose feedings. [6] [7]

Testing

Since the 1970s, the World Health Organization and other organizations interested in diabetes agreed on a standard dose and duration. [8]

Preparation

The patient is instructed not to restrict carbohydrate intake in the days or weeks before the test. [9] 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 kg (94 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 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. [10]

Procedure

  1. A zero time (baseline) blood sample is drawn.
  2. The patient is then given a measured dose (below) of glucose solution to drink within a 5-minute time frame.
  3. 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

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. [15]

Results

For gestational diabetes, the American College of Obstetricians and Gynecologists (ACOG) recommends a two-step procedure, wherein the first step is a 50 g glucose dose. [12] [16] If after 1 hour the blood glucose level is more than 7.8 mmol/L (140 mg/dL), [12] it is followed by a 100 g glucose dose. [12] The diagnosis of gestational diabetes is then defined by a blood glucose level meeting or exceeding the cutoff values on at least two intervals, [12] with cutoffs as follows: [12]

Sample method

The diagnosis criteria stated above by the World Health Organization (WHO) are for venous samples only (a blood sample taken from a vein in the arm). An increasingly popular method for measuring blood glucose is to sample capillary or finger-prick blood, which is less invasive, more convenient for the patient and requires minimal training to conduct. Though fasting blood glucose levels have been shown to be similar in both capillary and venous samples, postprandial blood glucose levels (those measured after a meal) can vary. [17] The diagnosis criteria issued by the WHO are only suitable for venous blood samples. Given the increasing popularity of capillary testing, the WHO has recommended that a conversion factor between the two sample types be calculated, but as of 2017 no conversion factor had been issued by the WHO, despite some medical professionals adopting their own.[ citation needed ] A 2020 study on pregnant women for gestational diabetes mellitus (GDM) found that 0-hour venous and capillary levels were similar, but that 2-hour samples were different. The authors compared their study with others, and concluded that capillary samples could be used for diagnosis of GDM during pregnancy using corrected cutoffs with acceptable accuracy in an antenatal care setting. [17]

Variations

A standard two-hour GTT (glucose tolerance test) is sufficient to diagnose or exclude all forms of diabetes mellitus at all but the earliest stages of development.

Longer tests have been used for a variety of other purposes, such as detecting reactive hypoglycemia or defining subsets of hypothalamic obesity. Insulin levels are sometimes measured to detect insulin resistance or deficiency. [18]

The GTT (glucose tolerance test) is of limited value in the diagnosis of reactive hypoglycemia, since normal levels do not preclude the diagnosis, abnormal levels do not prove that the patient's other symptoms are related to a demonstrated atypical OGTT, and many people without symptoms of reactive hypoglycemia may have the late low glucose. [19]

Oral glucose challenge test

The oral glucose challenge test (OGCT) is a short version of the OGTT, used to check pregnant women for signs of gestational diabetes. [3] [20] It can be done at any time of day, not on an empty stomach. [3] The test involves 50 g of glucose, with a reading after one hour. [3]

Limitations of OGTT

The OGTT does not distinguish between insulin resistance in peripheral tissues and reduced capacity of the pancreas beta-cells to produce insulin. The OGTT is less accurate than the hyperinsulinemic-euglycemic clamp technique (the "gold standard" for measuring insulin resistance), or the insulin tolerance test, but is technically less difficult. Neither of the two technically demanding tests can be easily applied in a clinical setting or used in epidemiological studies. HOMA-IR (homeostatic model assessment) is a convenient way of measuring insulin resistance in normal subjects, which can be used in epidemiological studies, but can give erroneous results for diabetic patients. [21] [22]

See also

Related Research Articles

<span class="mw-page-title-main">Hypoglycemia</span> Health condition

Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose below 70 mg/dL (3.9 mmol/L), symptoms associated with hypoglycemia, and resolution of symptoms when blood sugar returns to normal. Hypoglycemia may result in headache, tiredness, clumsiness, trouble talking, confusion, fast heart rate, sweating, shakiness, nervousness, hunger, loss of consciousness, seizures, or death. Symptoms typically come on quickly.

Insulin resistance (IR) is a pathological condition in which cells either fail to respond normally to the hormone insulin or downregulate insulin receptors in response to hyperinsulinemia.

The following is a glossary of diabetes which explains terms connected with diabetes.

<span class="mw-page-title-main">Diabetic ketoacidosis</span> Medical condition

Diabetic ketoacidosis (DKA) is a potentially life-threatening complication of diabetes mellitus. Signs and symptoms may include vomiting, abdominal pain, deep gasping breathing, increased urination, weakness, confusion and occasionally loss of consciousness. A person's breath may develop a specific "fruity" smell. The onset of symptoms is usually rapid. People without a previous diagnosis of diabetes may develop DKA as the first obvious symptom.

<span class="mw-page-title-main">Hyperglycemia</span> Too much blood sugar, usually because of diabetes

Hyperglycemia is a condition in which an excessive amount of glucose circulates in the blood plasma. This is generally a blood sugar level higher than 11.1 mmol/L (200 mg/dL), but symptoms may not start to become noticeable until even higher values such as 13.9–16.7 mmol/L (~250–300 mg/dL). A subject with a consistent fasting blood glucose range between ~5.6 and ~7 mmol/L is considered slightly hyperglycemic, and above 7 mmol/L is generally held to have diabetes. For diabetics, glucose levels that are considered to be too hyperglycemic can vary from person to person, mainly due to the person's renal threshold of glucose and overall glucose tolerance. On average, however, chronic levels above 10–12 mmol/L (180–216 mg/dL) can produce noticeable organ damage over time.

<span class="mw-page-title-main">Type 2 diabetes</span> Type of diabetes mellitus with high blood sugar and insulin resistance

Type 2 diabetes (T2D), formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urination, fatigue and unexplained weight loss. Symptoms may also include increased hunger, having a sensation of pins and needles, and sores (wounds) that do not heal. Often symptoms come on slowly. Long-term complications from high blood sugar include heart disease, stroke, diabetic retinopathy which can result in blindness, kidney failure, and poor blood flow in the limbs which may lead to amputations. The sudden onset of hyperosmolar hyperglycemic state may occur; however, ketoacidosis is uncommon.

<span class="mw-page-title-main">Blood sugar level</span> Concentration of glucose present in the blood (Glycaemia)

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.

<span class="mw-page-title-main">Gestational diabetes</span> Medical condition

Gestational diabetes is a condition in which a person without diabetes develops high blood sugar levels during pregnancy. Gestational diabetes generally results in few symptoms; however, it increases the risk of pre-eclampsia, depression, and of needing a Caesarean section. Babies born to individuals with poorly treated gestational diabetes are at increased risk of macrosomia, of having hypoglycemia after birth, and of jaundice. If untreated, diabetes can also result in stillbirth. Long term, children are at higher risk of being overweight and of developing type 2 diabetes.

<span class="mw-page-title-main">Insulinoma</span> Medical condition

An insulinoma is a tumour of the pancreas that is derived from beta cells and secretes insulin. It is a rare form of a neuroendocrine tumour. Most insulinomas are benign in that they grow exclusively at their origin within the pancreas, but a minority metastasize. Insulinomas are one of the functional pancreatic neuroendocrine tumour (PNET) group. In the Medical Subject Headings classification, insulinoma is the only subtype of "islet cell adenoma".

<span class="mw-page-title-main">Glucose meter</span> Medical device for determining the concentration of glucose in the blood

A glucose meter, also referred to as a "glucometer", is a medical device for determining the approximate concentration of glucose in the blood. It can also be a strip of glucose paper dipped into a substance and measured to the glucose chart. It is a key element of glucose testing, including home blood glucose monitoring (HBGM) performed by people with diabetes mellitus or hypoglycemia. A small drop of blood, obtained from slightly piercing a fingertip with a lancet, is placed on a disposable test strip that the meter reads and uses to calculate the blood glucose level. The meter then displays the level in units of mg/dL or mmol/L.

Steroid diabetes or steroid-induced diabetes is characterized as an unusual rise in blood sugar that is linked to the use of glucocorticoids in a patient who may or may not have had diabetes mellitus in the past.

The term diabetes includes several different metabolic disorders that all, if left untreated, result in abnormally high concentrations of a sugar called glucose in the blood. Diabetes mellitus type 1 results when the pancreas no longer produces significant amounts of the hormone insulin, usually owing to the autoimmune destruction of the insulin-producing beta cells of the pancreas. Diabetes mellitus type 2, in contrast, is now thought to result from autoimmune attacks on the pancreas and/or insulin resistance. The pancreas of a person with type 2 diabetes may be producing normal or even abnormally large amounts of insulin. Other forms of diabetes mellitus, such as the various forms of maturity-onset diabetes of the young, may represent some combination of insufficient insulin production and insulin resistance. Some degree of insulin resistance may also be present in a person with type 1 diabetes.

Many types of glucose tests exist and they can be used to estimate blood sugar levels at a given time or, over a longer period of time, to obtain average levels or to see how fast body is able to normalize changed glucose levels. Eating food for example leads to elevated blood sugar levels. In healthy people, these levels quickly return to normal via increased cellular glucose uptake which is primarily mediated by increase in blood insulin levels.

<span class="mw-page-title-main">Diabetes and pregnancy</span> Effects of pre-existing diabetes upon pregnancy

For pregnant women with diabetes, some particular challenges exist for both mother and fetus. If the pregnant woman has diabetes as a pre-existing disorder, it can cause early labor, birth defects, and larger than average infants. Therefore, experts advise diabetics to maintain blood sugar level close to normal range about 3 months before planning for pregnancy.

<span class="mw-page-title-main">Impaired fasting glucose</span> Medical condition

Impaired fasting glucose is a type of prediabetes, in which a person's blood sugar levels during fasting are consistently above the normal range, but below the diagnostic cut-off for a formal diagnosis of diabetes mellitus. Together with impaired glucose tolerance, it is a sign of insulin resistance. In this manner, it is also one of the conditions associated with metabolic syndrome.

An insulin tolerance test (ITT) is a medical diagnostic procedure during which insulin is injected into a patient's vein, after which blood glucose is measured at regular intervals. This procedure is performed to assess pituitary function, adrenal function, insulin sensitivity, and sometimes for other purposes. An ITT is usually ordered and interpreted by an endocrinologist.

Rabson–Mendenhall syndrome is a rare autosomal recessive disorder characterized by severe insulin resistance. The disorder is caused by mutations in the insulin receptor gene. Symptoms include growth abnormalities of the head, face and nails, along with the development of acanthosis nigricans. Treatment involves controlling blood glucose levels by using insulin and incorporating a strategically planned, controlled diet. Also, direct actions against other symptoms may be taken This syndrome usually affects children and has a prognosis of 1–2 years.

A random glucose test, also known as a random blood glucose test or a casual blood glucose test is a glucose test on the blood of a non-fasting person. This test assumes a recent meal and therefore has higher reference values than the fasting blood glucose (FBG) test.

<span class="mw-page-title-main">Prediabetes</span> Predisease state of hyperglycemia with high risk for diabetes

Prediabetes is a component of metabolic syndrome and is characterized by elevated blood sugar levels that fall below the threshold to diagnose diabetes mellitus. It usually does not cause symptoms but people with prediabetes often have obesity, dyslipidemia with high triglycerides and/or low HDL cholesterol, and hypertension. It is also associated with increased risk for cardiovascular disease (CVD). Prediabetes is more accurately considered an early stage of diabetes as health complications associated with type 2 diabetes often occur before the diagnosis of diabetes.

Oxyhyperglycemia is a special type of impaired glucose tolerance characterized by a rapid and transient hyperglycemia spike after an oral intake of glucose, the peak of this spike being high enough to cause transient, symptom free glycosuria, but this hyperglycemia reverses rapidly and may even go to hypoglycemia in the later phase. This sharp downstroke overshooting towards hypoglycemia distinguishes this pathologic phenomenon from the artificial hyperglycemia inducible by an intravenous bolus dose of a large amount of glucose solution. Early dumping syndrome patients usually have oxyhyperglycemia associated with any meal or OGTT.

References

  1. ↑ Glucose+Tolerance+Test at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  2. ↑ DeFronzo RA, Abdul-Ghani M (2011). "Assessment and treatment of cardiovascular risk in prediabetes: impaired glucose tolerance and impaired fasting glucose". American Journal of Cardiology . 108 (3 Suppl): 3B–24B. doi:10.1016/j.amjcard.2011.03.013. PMID   21802577.
  3. 1 2 3 4 Institute for Quality and Efficiency in Health Care. "Glucose tolerance test: how does it work exactly?". Informed Health Online. Institute for Quality and Efficiency in Health Care. Retrieved 22 June 2013.
  4. ↑ Conn, JW. (1940). "Interpretation of the glucose tolerance test. The necessity of a standard preparatory diet". Am J Med Sci. 199: 555–64. doi:10.1097/00000441-194004000-00014.
  5. ↑ "Jacobsen ATB. Untersuchungen über den Einfluss verschiedener Nahrungsmittel auf den Blutzucker bei normalen, zuckerkranken und graviden Personen. Biochem Z 1913; 56:471–94".{{cite journal}}: Cite journal requires |journal= (help)
  6. ↑ Traugott, K. (1922). "Über das Verhalten des Blutzuckerspiegels bei wiederholter und verschiedener Art enteraler Zuckerzufuhr and dessen Bedeutung für die Leberfunktion". Klin. Wochenschr. 1 (18): 892. doi:10.1007/BF01715866. S2CID   32368110.
  7. ↑ Staub, H. (1921). "Bahnung im intermediaren Zuckerstoffwechsel". Biochem. Z. 118: 93.
  8. ↑ American Diabetes Association (2013). "Standards of Medical Care in Diabetes—2013". Diabetes Care. 36 (Suppl 1): S11–S66. doi:10.2337/dc13-S011. ISSN   0149-5992. PMC   3537269 . PMID   23264422.
  9. ↑ Klein, Klara R.; Walker, Christopher P.; McFerren, Amber L.; Huffman, Halie; Frohlich, Flavio; Buse, John B. (2021). "Carbohydrate Intake Prior to Oral Glucose Tolerance Testing". Journal of the Endocrine Society. 5 (5): bvab049. doi: 10.1210/jendso/bvab049 . PMC   8059359 . PMID   33928207.
  10. ↑ Salvaggio, Heather L; Zaenglein, Andrea L (2010-08-09). "Examining the use of oral contraceptives in the management of acne". International Journal of Women's Health. 2: 69–76. doi: 10.2147/ijwh.s5915 . ISSN   1179-1411. PMC   2971728 . PMID   21072299.
  11. 1 2 World Health Organization and International Diabetes Federation (1999). Definition, diagnosis and classification of diabetes mellitus and its complications. Geneva, Switzerland: World Health Organization.
  12. 1 2 3 4 5 6 7 8 9 American Diabetes Association (20 December 2019). "2. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes—2020". Diabetes Care. 43 (Supplement 1): S14–S31. doi: 10.2337/dc20-S002 . PMID   31862745 . Retrieved 26 February 2020.
  13. ↑ Salford Royal NHS Trust. "Glucose Tolerance Tests in Primary Care" . Retrieved 2012-06-20.
  14. ↑ Jane Patmore (2009). "Oral Glucose Tolerance Tests: Protocol and Guidance" (PDF). Hull and East Riding Diabetes Network, Hull NHS teaching hospitals trust. Archived from the original (PDF) on 2012-05-06. Retrieved 2012-06-20.
  15. ↑ "Glucose - Urine". ucsfhealth.org. Retrieved 2022-10-17.
  16. ↑ Committee on Practice Bulletins—Obstetrics (February 2018). "ACOG Practice Bulletin No. 190: Gestational Diabetes Mellitus". Obstetrics & Gynecology. 131 (2): e49–e64. doi:10.1097/AOG.0000000000002501. PMID   29370047. S2CID   3395229.
  17. 1 2 Nevander, Sofia; Landberg, Eva; Blomberg, Marie; Ekman, Bertil; Lilliecreutz, Caroline (26 November 2020). "Comparison of Venous and Capillary Sampling in Oral Glucose Testing for the Diagnosis of Gestational Diabetes Mellitus: A Diagnostic Accuracy Cross-Sectional Study Using Accu-Chek Inform II". Diagnostics. 10 (12): 1011. doi: 10.3390/diagnostics10121011 . ISSN   2075-4418. PMC   7760160 . PMID   33255868.
  18. ↑ Lv, Xue; Fang, Kun; Hao, Wenqing; Han, Yuxin; Yang, Nailong; Yu, Qing (2020-12-02). "Identification of Reactive Hypoglycemia with Different Basic BMI and Its Causes by Prolonged Oral Glucose Tolerance Test". Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy. 13: 4717–4726. doi: 10.2147/DMSO.S280084 . ISSN   1178-7007. PMC   7719337 . PMID   33293845.
  19. ↑ Pant, Vivek; Mathema, Safala; Jha, Sandeep; Paudel, Sujay Dutta; Baral, Suman (2021-12-07). "The Detection of Postprandial Hypoglycemia with 5-Hour Oral Glucose Tolerance Test". EJIFCC. 32 (4): 451–457. ISSN   1650-3414. PMC   8751404 . PMID   35046763.
  20. ↑ Hartling, L; Dryden, DM; Guthrie, A; et al. (October 2012). Screening and Diagnosing Gestational Diabetes Mellitus. Agency for Healthcare Research and Quality. pp. 1–327. PMC   4781607 . PMID   24423035 . Retrieved 22 June 2013.{{cite book}}: |work= ignored (help)
  21. ↑ Muniyappa R, Lee S, Chen H, Quon MJ (2008). "Current approaches for assessing insulin sensitivity and resistance in vivo: advantages, limitations, and appropriate usage" . American Journal of Physiology. Endocrinology and Metabolism . 294 (1): E15–E26. doi:10.1152/ajpendo.00645.2007. PMID   17957034. S2CID   848540.
  22. ↑ Antuna-Puente B, Disse E, Rabasa-Lhoret R, Laville M, Capeau J, Bastard JP (2011). "How can we measure insulin sensitivity/resistance?". Diabetes & Metabolism. 37 (5): 179–88. doi:10.1016/j.diabet.2011.01.002. PMID   21435930.
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