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Glucose (Plasma) – 75-Minute Oral Glucose Tolerance Test (OGTT)

Published: August 9, 2026Updated: August 16, 2026

This test measures how your body processes glucose (sugar) over time after drinking a sugary liquid. It helps check for diabetes or how well your pancreas produces insulin.

Quick summary

["A 75-minute glucose tolerance test evaluates blood sugar control after consuming sugar, useful for diagnosing diabetes or prediabetes."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
21310-8
Short code
Glucose 75M p chal SerPl-mCnc
Synonyms
Glucose 75M p chal SerPl-mCnc
Category
glucose
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
70
Ref high
100
Critical range
50 N/A – 400 N/A
Fasting
true
Population
adult
Sex
all
Age range
18–65 years
CPT
82947
SNOMED
260395008
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may recommend this test if you have symptoms of diabetes (like frequent urination, extreme thirst, or unexplained weight loss), a family history of diabetes, or if you’re overweight and have other risk factors. It’s also used to monitor blood sugar levels in pregnant women (gestational diabetes) or after a previous diagnosis.

What to Expect During the Test

You’ll start by fasting (not eating or drinking anything except water) for at least 8 hours. After fasting, you’ll drink a sugary liquid containing 75 grams of glucose. Blood samples will be taken at baseline (before drinking) and then every 30 minutes up to 2 hours to measure your blood sugar levels.

Preparing for the Test

Follow your doctor’s instructions carefully. Avoid caffeine, alcohol, or strenuous activity 24 hours before the test. Wear comfortable clothing and plan to stay with the healthcare provider for the duration of the test.

What the Results Mean

The results help determine if your blood sugar levels are normal, impaired (prediabetes), or diabetic. Your doctor will interpret the results in relation to your symptoms and medical history.

Reference range

Fasting: 70-100 mg/dLN/A

Specimen: serum

Fasting for 8-12 hours required. Water is permitted. Avoid chewing gum and smoking before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

OGTT 75g Glucose Tolerance

Frequently asked questions

What does a high or low blood sugar reading mean during the OGTT?
High blood sugar readings after drinking the glucose solution may indicate diabetes or impaired glucose tolerance. Low readings (if they occur) could be due to insulin resistance or other factors, but this is less common in the first few hours of the test.
How long does it take to get my results back?
Results are typically available within 1–2 weeks after the test. Your doctor will discuss them with you during a follow-up visit.
Can I eat or drink anything after the test?
Yes, once the test is complete, you can resume your normal diet and activities. However, avoid sugary foods or drinks for at least 24 hours before your next test if scheduled.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy