Oral Glucose Tolerance Test (OGTT) Knowledge Assessment — Questions and Answers

Question 1: Which substrate does the brain preferentially use for energy, making stable blood glucose critical?

Fatty acids
Glucose (Correct answer)
Ketone bodies
Amino acids

Correct answer: Glucose

Under normal conditions the brain relies almost exclusively on glucose as its energy substrate, requiring tightly regulated blood glucose levels.

Question 2: Acute physiological stress such as surgery or serious infection affects OGTT reliability by:

Having no effect on glucose levels
Improving insulin sensitivity temporarily
Lowering glucose through increased metabolic rate
Raising glucose via counter-regulatory hormone release (Correct answer)

Correct answer: Raising glucose via counter-regulatory hormone release

Stress triggers release of cortisol, epinephrine, glucagon, and growth hormone, all of which raise blood glucose — making OGTT during acute illness invalid.

Question 3: How much glucose is typically used in the solution for a standard OGTT?

25 grams
50 grams
100 grams
75 grams (Correct answer)

Correct answer: 75 grams

The 75-gram glucose solution is the standard dose recommended by organizations like the World Health Organization (WHO) and the American Diabetes Association (ADA) for diagnosing diabetes and prediabetes in non-pregnant adults. This specific amount is chosen to provide a significant glucose load to challenge the body's insulin response. It helps reveal any impaired glucose metabolism accurately.

Question 4: How does a 1-hour plasma glucose ≥155 mg/dL during a 75g OGTT relate to clinical risk assessment?

It has no established clinical significance
It is associated with increased cardiovascular and diabetes risk (Correct answer)
Only the 2-hour value predicts cardiovascular risk
The 1-hour value is only relevant in gestational diabetes

Correct answer: It is associated with increased cardiovascular and diabetes risk

Emerging evidence and some guidelines indicate that a 1-hour glucose ≥155 mg/dL during a 75g OGTT identifies individuals at higher risk for cardiovascular disease and type 2 diabetes.

Question 5: What is considered a normal blood glucose level two hours after drinking the glucose solution?

Below 140 mg/dL (Correct answer)
Below 100 mg/dL
Below 180 mg/dL
Below 200 mg/dL

Correct answer: Below 140 mg/dL

A blood glucose level below 140 mg/dL two hours after drinking the glucose solution is considered normal. This indicates that the body is effectively processing and clearing the glucose from the bloodstream, demonstrating healthy glucose tolerance. Levels above this threshold suggest impaired glucose regulation.

Question 6: A blood glucose level between 140 and 199 mg/dL two hours after the OGTT indicates:

Prediabetes (Correct answer)
Type 1 diabetes
Type 2 diabetes
Normal glucose tolerance

Correct answer: Prediabetes

A blood glucose level between 140 and 199 mg/dL two hours after the OGTT indicates prediabetes, also known as impaired glucose tolerance. This range signifies that the body is not processing glucose as efficiently as it should, putting the individual at a higher risk of developing type 2 diabetes. It's a critical warning sign for intervention.

Question 7: For a non-pregnant adult, which set of values confirms diabetes via OGTT?

Fasting 95 mg/dL and 2-hour 155 mg/dL
Fasting 99 mg/dL and 2-hour 139 mg/dL
Fasting 110 mg/dL and 2-hour 180 mg/dL
Fasting 122 mg/dL and 2-hour 210 mg/dL (Correct answer)

Correct answer: Fasting 122 mg/dL and 2-hour 210 mg/dL

A 2-hour glucose of ≥200 mg/dL confirms diabetes; fasting ≥126 also confirms it — in this case both criteria are met.

Question 8: What is the normal renal glucose threshold at which glucosuria (glucose in urine) appears?

~180 mg/dL (Correct answer)
~100 mg/dL
~140 mg/dL
~250 mg/dL

Correct answer: ~180 mg/dL

Glucose appears in the urine when plasma glucose exceeds approximately 180 mg/dL, the renal tubular reabsorption threshold.

Question 9: An exaggerated early glucose peak at 30–60 minutes that returns fully to normal by 2 hours on an OGTT most likely suggests:

Diabetes mellitus
Dumping syndrome or accelerated gastric emptying (Correct answer)
Chronic renal failure
Adrenal insufficiency

Correct answer: Dumping syndrome or accelerated gastric emptying

An exaggerated early peak with rapid return to normal suggests accelerated gastric emptying or dumping syndrome, causing rapid glucose absorption followed by a brisk insulin response.

Question 10: What should a patient avoid before taking the OGTT to ensure accurate results?

Sugary drinks
High-protein foods
Physical exercise (Correct answer)
High-fat foods

Correct answer: Physical exercise

Patients should avoid strenuous physical exercise for at least 8-12 hours before an OGTT. Exercise can temporarily lower blood glucose levels by increasing glucose uptake by muscles, potentially leading to inaccurate or falsely normal test results. This precaution ensures that the body's baseline glucose metabolism is assessed without confounding factors.

Question 11: Which condition is characterized by the inability of beta cells to produce any insulin, making OGTT results extreme?

Reactive hypoglycemia
Impaired fasting glucose
Type 2 diabetes
Type 1 diabetes (Correct answer)

Correct answer: Type 1 diabetes

Type 1 diabetes results from autoimmune destruction of beta cells, causing absolute insulin deficiency and severely elevated glucose levels on OGTT.

Question 12: A 2-hour plasma glucose of 155 mg/dL following a 75g oral glucose load is classified as:

Normal glucose tolerance
Diabetes mellitus
Hypoglycemia
Impaired glucose tolerance (IGT) (Correct answer)

Correct answer: Impaired glucose tolerance (IGT)

A 2-hour glucose of 140–199 mg/dL after a 75g OGTT is classified as impaired glucose tolerance (IGT), a prediabetic state.

Question 13: What is the primary purpose of the oral glucose tolerance test (OGTT)?

To diagnose diabetes and prediabetes (Correct answer)
To measure cholesterol levels
To assess liver function
To evaluate kidney function

Correct answer: To diagnose diabetes and prediabetes

The primary purpose of the oral glucose tolerance test (OGTT) is to diagnose diabetes and prediabetes. It measures how well a person's body processes glucose over a period of time, revealing impaired glucose metabolism that might not be evident in a single fasting blood sugar test. This helps identify individuals at risk or with the condition.

Question 14: What fasting glucose threshold (Carpenter-Coustan criteria) identifies gestational diabetes on a 100 g OGTT?

≥126 mg/dL
≥105 mg/dL
≥95 mg/dL (Correct answer)
≥90 mg/dL

Correct answer: ≥95 mg/dL

Under Carpenter-Coustan criteria, a fasting glucose of ≥95 mg/dL on the 100 g OGTT is one of the four diagnostic thresholds for GDM.

Question 15: During the OGTT, what type of solution is the patient required to drink?

Saline solution
Electrolyte drink
Protein shake
Glucose solution (Correct answer)

Correct answer: Glucose solution

During the OGTT, the patient is required to drink a precisely measured glucose solution. This solution provides a standardized glucose load, allowing healthcare professionals to observe how the body's insulin response and glucose metabolism handle a significant sugar intake over time.

Question 16: Patients should inform their provider about all medications before an OGTT because:

All drugs must be stopped 24 hours before the test
Medication use disqualifies the patient from testing
Some drugs can cause false-positive or false-negative glucose readings (Correct answer)
Medications delay glucose absorption regardless of type

Correct answer: Some drugs can cause false-positive or false-negative glucose readings

Certain drugs such as corticosteroids, thiazide diuretics, and beta-blockers can significantly alter glucose levels, affecting test accuracy.

Question 17: A patient with a borderline prediabetes OGTT result should be counseled about which dietary target to reduce diabetes risk?

Reducing refined carbohydrates and added sugars while increasing fiber (Correct answer)
Increasing simple sugar intake for energy
Zero fat intake
Eliminating all protein from the diet

Correct answer: Reducing refined carbohydrates and added sugars while increasing fiber

Reducing refined carbohydrates and added sugars while increasing dietary fiber improves insulin sensitivity and reduces post-meal glucose excursions, lowering diabetes risk.

Question 18: Which medication class is most commonly asked to be temporarily discontinued before an OGTT if medically safe?

Beta-blockers
Antibiotics
Oral contraceptives (Correct answer)
Antihistamines

Correct answer: Oral contraceptives

Oral contraceptives can impair glucose tolerance and may be temporarily held before testing when clinically appropriate.

Question 19: When comparing ADA and WHO interpretation criteria for the standard 75g OGTT, which statement is correct?

ADA uses 180 mg/dL and WHO uses 200 mg/dL as the 2-hour diabetes threshold
Both use ≥200 mg/dL as the 2-hour diagnostic threshold for diabetes (Correct answer)
ADA requires three abnormal values while WHO requires only one
WHO does not use OGTT for diabetes diagnosis

Correct answer: Both use ≥200 mg/dL as the 2-hour diagnostic threshold for diabetes

Both the ADA and WHO use ≥200 mg/dL as the 2-hour plasma glucose threshold for diabetes diagnosis using the 75g OGTT.

Question 20: Why does an oral glucose load produce a greater insulin response than the same glucose given intravenously?

Oral absorption is faster
Oral glucose stimulates cortisol release
The incretin effect amplifies pancreatic insulin secretion (Correct answer)
Intravenous glucose bypasses the liver

Correct answer: The incretin effect amplifies pancreatic insulin secretion

Gut-derived incretin hormones (GLP-1, GIP) released during oral glucose ingestion amplify insulin secretion, producing a greater response than IV glucose — known as the 'incretin effect.'

Question 21: How many hours of fasting are required before taking the OGTT?

4 hours
2 hours
12 hours
8 hours (Correct answer)

Correct answer: 8 hours

Before taking the OGTT, a patient is typically required to fast for 8 hours. This fasting period ensures that the baseline blood glucose level is not influenced by recent food intake, providing an accurate starting point for the test. It's crucial for reliable results.

Question 22: How many abnormal values on the 100 g 3-hour OGTT are required to diagnose gestational diabetes (Carpenter-Coustan)?

Three
Two (Correct answer)
Four
One

Correct answer: Two

A diagnosis of GDM under Carpenter-Coustan criteria requires two or more abnormal values on the 4-point 100 g OGTT.

Question 23: During the OGTT, what type of solution is the patient required to drink?

Saline solution
Glucose solution (Correct answer)
Electrolyte drink
Protein shake

Correct answer: Glucose solution

During the OGTT, the patient is required to drink a specific glucose solution. This solution contains a measured amount of sugar designed to challenge the body's ability to regulate blood glucose, allowing healthcare professionals to observe the insulin response and glucose clearance over time. It's the key component for assessing glucose tolerance.

Question 24: Hyperthyroidism affects OGTT interpretation because thyroid hormones:

Slow intestinal glucose absorption
Lower fasting glucose by stimulating glycogenesis
Accelerate glucose absorption and increase hepatic glucose output, elevating post-load glucose (Correct answer)
Improve beta-cell function

Correct answer: Accelerate glucose absorption and increase hepatic glucose output, elevating post-load glucose

Excess thyroid hormones accelerate gastrointestinal glucose absorption and increase hepatic glucose output, causing an exaggerated early OGTT peak.

Question 25: What is the standard glucose load given to a non-pregnant adult during an OGTT?

75 g (Correct answer)
150 g
50 g
100 g

Correct answer: 75 g

The standard OGTT for non-pregnant adults uses a 75 g oral glucose load dissolved in water.

Question 26: Postpartum testing after GDM should include an OGTT at which interval?

4–12 weeks postpartum (Correct answer)
2 weeks postpartum
1 year postpartum
6 months postpartum

Correct answer: 4–12 weeks postpartum

ADA recommends a 75 g 2-hour OGTT at 4–12 weeks postpartum to reassess glucose metabolism after GDM.

Question 27: Which pancreatic cell type releases glucagon to counter hypoglycemia?

Delta cells
PP cells
Alpha cells (Correct answer)
Beta cells

Correct answer: Alpha cells

Alpha cells in the pancreatic islets secrete glucagon, which stimulates hepatic glycogenolysis and gluconeogenesis to raise blood glucose.

Question 28: For how long after glucose ingestion are blood draws typically taken in a standard 2-hour OGTT?

60 minutes
30 minutes
120 minutes (Correct answer)
180 minutes

Correct answer: 120 minutes

In the standard 2-hour OGTT, blood is drawn at fasting baseline and again at 120 minutes post-ingestion.

Question 29: Alcohol consumption the night before an OGTT can cause:

Falsely high 2-hour glucose
Increased insulin secretion
No change in results
Falsely low fasting glucose due to inhibition of hepatic gluconeogenesis (Correct answer)

Correct answer: Falsely low fasting glucose due to inhibition of hepatic gluconeogenesis

Alcohol inhibits hepatic gluconeogenesis, which can cause falsely low fasting glucose on an OGTT performed the morning after drinking.

Question 30: HIV antiretroviral therapy, particularly protease inhibitors, can affect OGTT by:

Improving glucose metabolism
Lowering fasting glucose
Having no metabolic effect
Causing lipodystrophy and insulin resistance, raising OGTT values (Correct answer)

Correct answer: Causing lipodystrophy and insulin resistance, raising OGTT values

HIV protease inhibitors disrupt adipocyte function causing lipodystrophy and severe insulin resistance, which can produce markedly abnormal OGTT results.

Question 31: According to ADA criteria, what is the 2-hour plasma glucose value that confirms diabetes during an OGTT?

≥250 mg/dL
≥200 mg/dL (Correct answer)
≥140 mg/dL
≥180 mg/dL

Correct answer: ≥200 mg/dL

A 2-hour plasma glucose of ≥200 mg/dL during a 75 g OGTT confirms a diagnosis of diabetes mellitus per ADA guidelines.

Question 32: Which transporter is responsible for insulin-stimulated glucose uptake in skeletal muscle?

GLUT5
GLUT4 (Correct answer)
GLUT1
GLUT2

Correct answer: GLUT4

GLUT4 is the insulin-sensitive glucose transporter that translocates to the cell membrane in response to insulin, allowing glucose into muscle and fat cells.

Question 33: How many hours of fasting are required before taking the OGTT?

12 hours
8 hours (Correct answer)
2 hours
4 hours

Correct answer: 8 hours

A fasting period of at least 8 hours, but no more than 14 hours, is required before an OGTT. This ensures that the patient's baseline blood glucose level is not influenced by recent food intake. It provides an accurate starting point for assessing the body's response to the glucose load.

Question 34: Which metabolic pathway converts excess post-meal glucose into fatty acids for long-term energy storage?

Gluconeogenesis
Beta-oxidation
Ketogenesis
De novo lipogenesis (Correct answer)

Correct answer: De novo lipogenesis

De novo lipogenesis is the hepatic conversion of surplus glucose-derived acetyl-CoA into fatty acids, stored as triglycerides in adipose tissue.

Question 35: Which laboratory value, when combined with the 2-hour OGTT result, provides the most complete picture of glucose tolerance?

Fasting plasma glucose (Correct answer)
Urine glucose
Serum ketones
Random plasma glucose

Correct answer: Fasting plasma glucose

Fasting plasma glucose combined with the 2-hour OGTT value assesses both basal insulin secretion and post-challenge glucose clearance comprehensively.

Question 36: What blood glucose level two hours after the OGTT confirms a diagnosis of diabetes?

140 mg/dL
160 mg/dL
200 mg/dL or higher (Correct answer)
180 mg/dL

Correct answer: 200 mg/dL or higher

A blood glucose level of 200 mg/dL or higher two hours after the OGTT confirms a diagnosis of diabetes. This elevated level indicates a significant impairment in the body's ability to regulate blood sugar, consistent with diabetic hyperglycemia. It's a definitive diagnostic criterion for the condition.

Question 37: The IADPSG recommends diagnosing gestational diabetes when fasting glucose exceeds which value?

95 mg/dL
100 mg/dL
85 mg/dL
92 mg/dL (Correct answer)

Correct answer: 92 mg/dL

IADPSG criteria diagnose gestational diabetes when fasting plasma glucose is ≥92 mg/dL, lower than the traditional Carpenter-Coustan threshold of 95 mg/dL.

Question 38: How long after drinking the glucose solution are blood samples typically taken in the OGTT?

Immediately and at 60 minutes
Immediately and at 1, 2, and 3 hours (Correct answer)
Only after 2 hours
Immediately and at 30 minutes

Correct answer: Immediately and at 1, 2, and 3 hours

In the OGTT, blood samples are typically taken immediately (fasting) and then at specific intervals after drinking the glucose solution, commonly at 1, 2, and 3 hours. This series of measurements allows healthcare providers to track the body's glucose response curve over time, providing comprehensive data on how glucose is metabolized. The 2-hour mark is particularly important for diagnosis.

Question 39: What is the fasting glucose threshold for GDM diagnosis on the 75 g one-step OGTT (IADPSG criteria)?

≥85 mg/dL
≥110 mg/dL
≥92 mg/dL (Correct answer)
≥100 mg/dL

Correct answer: ≥92 mg/dL

The IADPSG fasting threshold is ≥92 mg/dL, which is lower than the non-pregnant IFG cutoff, reflecting the physiological need for tighter glucose control in pregnancy.

Question 40: A patient's OGTT 2-hour value is 145 mg/dL. What is the typical first-line intervention?

Immediate insulin therapy
Dietary modification and increased physical activity (Correct answer)
Oral hypoglycemic agents
No intervention; repeat in 5 years

Correct answer: Dietary modification and increased physical activity

Impaired glucose tolerance (2-hour glucose 140–199 mg/dL) is managed first with lifestyle interventions—diet and exercise—to prevent progression to diabetes.

Question 41: Which organ is primarily responsible for removing glucose from the bloodstream after an oral glucose load?

Pancreas
Skeletal muscle and liver (Correct answer)
Small intestine
Kidneys

Correct answer: Skeletal muscle and liver

After glucose absorption, skeletal muscle and the liver are the primary tissues that take up and store glucose, driven by insulin stimulation.

Question 42: A patient's 2-hour OGTT result is 160 mg/dL. What is the correct interpretation?

Impaired glucose tolerance (prediabetes) (Correct answer)
Diabetes mellitus
Normal glucose tolerance
Reactive hypoglycemia

Correct answer: Impaired glucose tolerance (prediabetes)

A 2-hour glucose of 140–199 mg/dL is classified as impaired glucose tolerance, a form of prediabetes requiring lifestyle intervention.

Question 43: Which hormone's function is primarily assessed by the OGTT?

Glucagon
Adrenaline
Insulin (Correct answer)
Cortisol

Correct answer: Insulin

The OGTT primarily assesses the body's ability to produce and respond to insulin, the hormone responsible for regulating blood glucose levels. By measuring how quickly glucose is cleared from the blood after a glucose load, the test evaluates the efficiency of insulin secretion and action. This helps in maintaining glucose homeostasis.

Question 44: Which class of medication used for HIV treatment is specifically associated with decreased peripheral glucose disposal on OGTT?

Integrase inhibitors
Entry inhibitors
Nucleoside reverse transcriptase inhibitors (NRTIs)
Protease inhibitors (Correct answer)

Correct answer: Protease inhibitors

Protease inhibitors interfere with GLUT4 trafficking in peripheral tissues, acutely reducing glucose disposal and causing elevated post-load glucose on OGTT.

Question 45: What is the primary hormone released by the pancreas in response to elevated blood glucose?

Epinephrine
Cortisol
Glucagon
Insulin (Correct answer)

Correct answer: Insulin

Beta cells in the pancreatic islets of Langerhans secrete insulin in response to rising blood glucose, facilitating cellular glucose uptake.

Question 46: A woman's 3-hour 100 g OGTT shows one abnormal value under Carpenter-Coustan criteria. The correct interpretation is:

Immediate insulin therapy is warranted
Gestational diabetes is confirmed
Results are normal; no action needed
Borderline result; repeat testing or lifestyle counseling may be recommended (Correct answer)

Correct answer: Borderline result; repeat testing or lifestyle counseling may be recommended

One abnormal value on the 100 g OGTT does not meet the two-value threshold for GDM diagnosis but indicates increased risk and warrants counseling and possible repeat testing.

Question 47: Which drug class is well-known for causing hyperglycemia that can produce a false-positive OGTT?

Loop diuretics
Beta-blockers
Corticosteroids (Correct answer)
ACE inhibitors

Correct answer: Corticosteroids

Corticosteroids (e.g., prednisone) raise blood glucose by stimulating hepatic gluconeogenesis and inducing insulin resistance, potentially producing false-positive OGTT results.

Question 48: What long-term risk does a history of GDM confer on the mother?

No increased risk after delivery
Decreased risk of autoimmune diabetes
Increased risk of gestational hypertension only
7-fold increased risk of developing type 2 diabetes (Correct answer)

Correct answer: 7-fold increased risk of developing type 2 diabetes

Women with a history of GDM have approximately a 7-fold increased lifetime risk of developing type 2 diabetes compared to women with normoglycemic pregnancies.

Question 49: In which population is a 100-gram glucose solution used for the OGTT?

Athletes
Children
Pregnant women (Correct answer)
Elderly patients

Correct answer: Pregnant women

A 100-gram glucose solution is specifically used for the 3-hour oral glucose tolerance test (OGTT) in pregnant women to screen for gestational diabetes. This higher dose and longer test duration are necessary to detect the subtle glucose intolerance that can occur during pregnancy. This is crucial for managing maternal and fetal health.

Question 50: What is the role of the incretin hormone GLP-1 during an oral glucose tolerance test?

Promotes hepatic glucose output
Stimulates gastric emptying
Enhances glucose-stimulated insulin secretion and suppresses glucagon (Correct answer)
Suppresses insulin secretion

Correct answer: Enhances glucose-stimulated insulin secretion and suppresses glucagon

GLP-1 (glucagon-like peptide-1) is released from intestinal L-cells during oral glucose ingestion and amplifies insulin secretion while suppressing glucagon, lowering post-meal glucose.

Oral Glucose Tolerance Test (OGTT) Knowledge Assessment

A knowledge assessment covering the procedures, physiology, interpretation, and clinical considerations of the Oral Glucose Tolerance Test (OGTT), used to diagnose prediabetes, type 2 diabetes, and gestational diabetes.

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75 min

Time Limit

70%

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