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Blood Test Tracker

Glucose, OGTT 1-Hour

Blood glucose one hour after a measured sugar drink in an oral glucose tolerance test. In pregnancy, a high 1-hour value is one criterion for gestational diabetes.

AI-verified against cited sources. Awaiting expert reviewAlso called 1h-PG, 1-h PG, OGTT-1hLOINC 1507-3

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What it is

An oral glucose tolerance test (OGTT) shows how your body handles a sugar load. After an overnight fast you have a blood draw. Then you drink a measured amount of glucose, usually 75 or 100 grams, and your blood is drawn again at set times. This result is the sample taken one hour after the drink. Outside pregnancy, the 1-hour value is not part of the American Diabetes Association (ADA) criteria, though the International Diabetes Federation (IDF) proposed cut points for it in 2024. In pregnancy, it is one of the values used to look for gestational diabetes.

Why it matters

The 1-hour sample shows how your glucose responds early in the test. In pregnancy, the ADA treats a 1-hour value of 180 mg/dL (10.0 mmol/L) or higher as one of the thresholds for gestational diabetes. Outside pregnancy, the IDF reports that a 1-hour value of 155 mg/dL (8.6 mmol/L) or higher predicts a higher chance of developing type 2 diabetes, even in people whose 2-hour value is in the usual range. Most guidelines still rely on the 2-hour value, so your clinician reads the whole test together.

If it’s high

In pregnancy, a 1-hour result of 180 mg/dL (10.0 mmol/L) or higher meets one of the ADA thresholds for gestational diabetes. Outside pregnancy, the IDF considers 155 mg/dL (8.6 mmol/L) or higher intermediate hyperglycaemia and 209 mg/dL (11.6 mmol/L) or higher the diabetes range, with a repeat test to confirm. These IDF cut points are newer than the ADA's 2-hour criteria, and the ADA 2026 Standards do not use a 1-hour value outside pregnancy. A high number can also have everyday explanations, such as illness or not fasting.

Common causes

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

What can help

  • Ask your clinician how your fasting, 1-hour and 2-hour values fit together, since they are read as a set
  • If you are pregnant, ask what the next steps are and which glucose goals apply to you
  • Regular physical activity and balanced meals are the main lifestyle levers clinicians discuss for glucose that runs high

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.

IDF 2024 position statement: 1-hour glucose after a 75 g load (not for pregnancy; not yet in ADA criteria)

  • Below the IDF cut pointbelow 155 mg/dL
  • Intermediate hyperglycaemia (IDF)155 to under 209 mg/dL
  • Diabetes range (IDF; needs a repeat test to confirm)209 and above mg/dL

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
  • 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 size of the glucose load matters: 75 g, 100 g and the 50 g screening drink give 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, then the sugar drink. Sample taken exactly 1 hour after the drink. Reflects test day only. For a 2 to 3 month average, look at A1c.

When to talk to a clinician

If your result meets a pregnancy threshold and you haven't heard from your clinician, call to ask 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?
  • Which criteria is my lab using, and which glucose load did I have?
  • How do my fasting, 1-hour and 2-hour values fit together?
  • What are the next steps, and when should we recheck?

Questions people ask

Why are there different limits for my 1-hour result?

The limit depends on whether you are pregnant and on the size of the drink. In pregnancy, the ADA uses 180 mg/dL (10.0 mmol/L) for both the 75 g and 100 g (Carpenter-Coustan) tests, and some labs use the older 190 mg/dL for the 100 g test. Outside pregnancy, only the IDF has proposed cut points for the 1-hour value. Check which test and criteria your lab used.

Is the 1-hour glucose used to diagnose diabetes?

Not in the ADA 2026 criteria, which use the 2-hour value, fasting glucose or A1c. The IDF (2024) proposes that a 1-hour value of 209 mg/dL (11.6 mmol/L) or higher is in the diabetes range and should be confirmed by a repeat test. Your clinician decides which criteria apply.

Is this the same as the 1-hour glucose challenge test in pregnancy?

No. The glucose challenge test uses a 50 g drink, needs no fasting and has its own cutoffs of 130, 135 or 140 mg/dL. This result is the 1-hour sample of a longer, fasting OGTT with a 75 g or 100 g drink.

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 1-Hour Glucose unit converter

For clinicians and researchers

Venous plasma or serum glucose at 60 minutes of an OGTT. ADA 2026 (Section 2): the one-step strategy uses a 75 g load after an overnight fast of at least 8 hours, with gestational diabetes diagnosed when any one of fasting 92, 1-hour 180 or 2-hour 153 mg/dL (5.1, 10.0, 8.5 mmol/L) is met or exceeded; these IADPSG cut points come from the HAPO study and mark the average values at which the odds of adverse outcomes reached 1.75 times the estimated odds. The two-step strategy uses a nonfasting 50 g load with a 1-hour screen at 130, 135 or 140 mg/dL, then a fasting 100 g test with Carpenter-Coustan thresholds of 95, 180, 155 and 140 mg/dL, where two or more values are needed (ACOG notes one can be used). The NDDG (1979) thresholds for the 100 g test are 105, 190, 165 and 145 mg/dL, per a published review of GDM criteria. Outside pregnancy the ADA diagnostic criteria use the 2-hour value of a 75 g OGTT, the fasting value, or A1c. The IDF position statement (2024) reviews evidence that a 1-hour value of 155 mg/dL (8.6 mmol/L) or higher in people with normal glucose tolerance predicts progression to type 2 diabetes and complications, and proposes 155 mg/dL for intermediate hyperglycaemia and 209 mg/dL (11.6 mmol/L) for type 2 diabetes, confirmed by a repeat test. The ADA 2026 Standards list no 1-hour diagnostic value outside pregnancy.

LOINC 1507-3 (primary), 51597-3, 1501-6, 14753-8. 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. Review of the Screening Guidelines for Gestational Diabetes Mellitus: How to Choose Wisely, Indian Journal of Community Medicine (2023)
  3. International Diabetes Federation Position Statement on the 1-hour post-load plasma glucose for the diagnosis of intermediate hyperglycaemia and type 2 diabetes, Diabetes Research and Clinical Practice (International Diabetes Federation) (2024)
  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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