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Glucose, OGTT 2-Hour

Blood glucose two hours after a 75 g sugar drink. It is the main OGTT value used to sort glucose tolerance into normal, prediabetes and diabetes ranges.

AI-verified against cited sources. Awaiting expert reviewAlso called 2hPG, 2-h PG, OGTT-2hLOINC 1518-0

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What it is

In an oral glucose tolerance test (OGTT) you fast overnight, give a blood sample, drink a measured sugar solution, and give more blood at set times. The 2-hour sample shows how well your body cleared the sugar. It is the value the American Diabetes Association (ADA) and International Diabetes Federation (IDF) use to define impaired glucose tolerance and one of the ways to diagnose diabetes. In pregnancy the same sample is one of the values used to look for gestational diabetes. It is not the same as a glucose check 2 hours after an ordinary meal.

Why it matters

Fasting glucose, A1c and the 2-hour OGTT value each show a different side of glucose handling, and the ADA notes that the 2-hour value picks up more people with prediabetes and diabetes than the other two. A result in the prediabetes range is a prompt to talk about steps that lower the chance of type 2 diabetes. In pregnancy, a high result can lead to extra monitoring to protect both parent and baby. One result isn't a diagnosis on its own, and your clinician reads it with your other tests.

If it’s low

A low 2-hour result is unusual. A sample that sat too long before testing can read falsely low. Some people also see their glucose dip a few hours after the sugar drink as insulin catches up. Low glucose can cause shakiness, sweating and confusion, and a low number with those symptoms is worth discussing with a clinician.

Common causes

  • A sample that sat for hours before the blood cells were separated
  • A drop in glucose after the sugar load (sometimes called reactive hypoglycemia)
  • A very long fast before the test, or heavy alcohol use
  • Liver or kidney disease
  • Underactive adrenal glands or certain pituitary conditions
  • Rarely, a pancreas tumor that makes too much insulin

What can help

  • If you had symptoms during the test, tell the person doing it and your clinician
  • Ask whether more testing is needed to understand a low result
  • Ask whether the sample handling or timing could explain it

If it’s high

Outside pregnancy, a 2-hour value of 140 to 199 mg/dL (7.8 to 11.0 mmol/L) is called impaired glucose tolerance by the ADA, which sits in the prediabetes range. A value of 200 mg/dL (11.1 mmol/L) or higher is in the diabetes range. Unless you have clear symptoms of very high glucose, the ADA looks for two results in the diabetes range, either from two different tests (even drawn together) or from the same test repeated. In pregnancy, a 2-hour value of 153 mg/dL (8.5 mmol/L) or higher on the 75 g test meets one of the thresholds for gestational diabetes.

Common causes

  • Prediabetes or diabetes
  • Gestational diabetes, when tested during pregnancy
  • Not fasting, or not following the test preparation
  • Illness, infection or other stress on the body
  • Some medicines, such as corticosteroids
  • Pancreas problems, such as pancreatitis

What can help

  • Ask your clinician how your fasting and 2-hour values fit together and whether to add an A1c
  • Regular physical activity, a balanced eating pattern and a healthy weight are the main lifestyle levers clinicians discuss for glucose that runs high
  • If you are pregnant, ask what the next steps are and which glucose goals apply to you
  • Ask whether any of your medicines could be raising your glucose

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex. Choose women or men to see the one that applies.

See OGTT 2-Hour Glucose by age and sex, with the U.S. survey numbers where they exist.

ADA / IDF categories for the 2-hour glucose after a 75 g load (not pregnancy)

  • Normal glucose tolerancebelow 140 mg/dL
  • Impaired glucose tolerance (prediabetes range)140 to under 200 mg/dL
  • Diabetes range (needs a confirming result)200 and above mg/dL

If this applies to you

OGTT 2-Hour Glucose means a little more for some people. Open the one that fits you.

PCOS

The guideline calls the 75 g oral glucose tolerance test (OGTT) the most accurate way to check blood sugar in PCOS, at any body weight. It also suggests one when planning pregnancy or fertility treatment.

Blood tests for PCOS

Pregnant or postpartum

The glucose tolerance test is used to check for gestational diabetes. After gestational diabetes, the ADA suggests this test again 4 to 12 weeks after birth, then lifelong checks for prediabetes or diabetes every 1 to 3 years.

Blood tests in pregnancy and after birth

How common is your level?

NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.

How OGTT 2-Hour Glucose varies with age in the U.S.Shaded: middle 90% and middle 50% of people. Line: the median. mg/dL. Point at any age, or focus the chart and use the arrow keys, to read both sexes in words.

Use the left and right arrow keys to read each age. Shift moves five years.

Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.

Explore OGTT 2-Hour Glucose by age and sex: every percentile as a table, with a download.

What can affect your result

  • Which glucose load was used: 75 g, 100 g, or the 50 g screening drink
  • Fasting for at least 8 hours beforehand, and a normal routine on the days before
  • Pregnancy and how far along it is
  • Illness, stress, surgery or injury
  • Medicines, including corticosteroids
  • Sample handling: unspun blood loses glucose as cells use it
  • Not fasting for at least 8 hours beforehand, or eating or drinking anything besides water during the test, can change results.
  • The ADA diagnostic criteria use a 75 g load. A 100 g (pregnancy) or 50 g (screening) drink gives results that are not interchangeable.
  • Illness, infection, surgery and other physical stress raise glucose, as can some medicines (for example corticosteroids).
  • Vomiting the drink can make the result unreliable.
  • A sample that sits before the blood cells are separated can read falsely low, because the cells use up glucose in the tube.

Morning, after an overnight fast of at least 8 hours (ADA). Sample taken exactly 2 hours after the drink. Reflects test day only. For a 2 to 3 month average, look at A1c.

When to talk to a clinician

If the result is 200 mg/dL (11.1 mmol/L) or higher and no one has gone over it with you, book a visit to talk about confirming it. If you are pregnant and the result meets a threshold, call your clinician about next steps. Contact the clinician who ordered the test today if the lab flagged the result as critical. Call 911 or your local emergency number for confusion, fainting or seizures, or for very high glucose with vomiting, belly pain, fast breathing or extreme drowsiness.

Questions you could ask

  • Was this a 75 g or a 100 g test, and was I fasting properly?
  • How often should my glucose be rechecked?
  • Should we repeat this test or check an A1c to confirm?
  • What steps could lower my chance of developing diabetes?
  • If I am pregnant, what are the next steps and glucose goals?
  • Could the sample handling or timing explain a low result?

Questions people ask

Is the 2-hour OGTT value the same as a 2-hour post-meal glucose?

No. The OGTT uses a measured sugar drink after an overnight fast, and its cutoffs (140 and 200 mg/dL) were set for that protocol. A glucose check after an ordinary meal is a different test, and its result depends on what you ate. Some reports use the word "postprandial" for the OGTT value, so check which test you had.

My result is between 140 and 199 mg/dL. What does that mean?

The ADA calls this impaired glucose tolerance, which is in the prediabetes range. It means your glucose was higher than usual two hours after the drink, not that you have diabetes. Your clinician can talk with you about repeating the test and about steps that may lower the chance of developing type 2 diabetes.

Why does my pregnancy result use a different number?

In pregnancy, the 75 g test uses a 2-hour threshold of 153 mg/dL (8.5 mmol/L). The 100 g test uses 155 mg/dL (8.6 mmol/L) in the Carpenter-Coustan criteria, and some labs use the older 165 mg/dL. These thresholds were set from pregnancy outcomes, so they are lower than the 140 and 200 mg/dL cutoffs used outside pregnancy.

Show the science and sources

Units

  • 1 mg/dL = 1 mg/dL
  • 1 mg/dL = 0.05551 mmol/L
  • 1 mg/dL = 0.01 g/L

Open the OGTT 2-Hour Glucose unit converter

For clinicians and researchers

Venous plasma glucose at 120 minutes of a WHO-style OGTT using 75 g anhydrous glucose. ADA 2026: diabetes if 2-hour plasma glucose is 200 mg/dL (11.1 mmol/L) or higher; impaired glucose tolerance (prediabetes) if 140 to 199 mg/dL (7.8 to 11.0 mmol/L). In the absence of unequivocal hyperglycemia, diagnosis needs two results in the diabetes range from different tests (possibly drawn together) or the same test at two time points. The ADA states that the 2-hour value is significantly more sensitive than fasting glucose or A1c and is preferred for some settings, such as cystic fibrosis-related and posttransplant diabetes. The IDF 2017 table uses the same thresholds. In pregnancy: the 75 g one-step strategy diagnoses gestational diabetes when any one of fasting 92, 1-hour 180 or 2-hour 153 mg/dL is met or exceeded (IADPSG, derived from HAPO); the 100 g two-step strategy uses Carpenter-Coustan 95, 180, 155 and 140 mg/dL with two or more values required (ACOG notes one can be used), while the NDDG (1979) thresholds are 105, 190, 165 and 145 mg/dL. In India, the DIPSI approach for pregnancy uses a nonfasting 75 g load with a 2-hour cut point of 140 mg/dL (whole blood). Postpartum, the ADA advises a 75 g OGTT at 4 to 12 weeks using nonpregnancy criteria. Plasma must be separated promptly or collected with a glycolysis inhibitor.

LOINC 1518-0 (primary), 14995-5, 1514-9, 14757-9. Specimen: serum-or-plasma.

Sources

  1. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2026, American Diabetes Association (Diabetes Care) (2026)
  2. IDF Clinical Practice Recommendations for managing Type 2 Diabetes in Primary Care, International Diabetes Federation (2017)
  3. Review of the Screening Guidelines for Gestational Diabetes Mellitus: How to Choose Wisely, Indian Journal of Community Medicine (2023)
  4. Glucose (PubChem compound 5793), PubChem, National Library of Medicine
  5. Critical Values List (CORP-APPEND-0104A, Rev. 46), ARUP Laboratories (2026)
  6. Critical (Panic) Values, with adult reference intervals (document DX_TL_811850, 01/19/2024), Labcorp (2024)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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