Question
A 55-year-old lady undergoes a standard 75 g oral glucose tolerance test for evaluation of possible abnormal sugar levels. Her results are as follows:
- Fasting glucose: 5.8 mmol/L
- 2-hour glucose: 8.6 mmol/L
What is the most appropriate interpretation of these findings?
a) Combined fasting and post-load glucose abnormality
b) Completely normal glucose regulation
c) Overt diabetes mellitus
d) Post-load glucose abnormality only
e) Isolated fasting glucose abnormality
Answer
Post-load glucose abnormality only (Impaired glucose tolerance)
Detailed Explanation
The diagnosis is based on WHO criteria for glucose metabolism:
- Normal:
- Fasting < 6.1 mmol/L
- 2-hour < 7.8 mmol/L
- Impaired fasting glucose (IFG):
- Fasting 6.1–6.9 mmol/L
- Impaired glucose tolerance (IGT):
- Fasting < 7.0 mmol/L
- 2-hour 7.8–11.0 mmol/L
- Diabetes mellitus:
- Fasting ≥ 7.0 mmol/L OR
- 2-hour ≥ 11.1 mmol/L
👉 In this case:
- Fasting = 5.8 → normal (not IFG)
- 2-hour = 8.6 → falls in 7.8–11.1 range
Hence, this is Impaired Glucose Tolerance (IGT).
IGT represents postprandial dysglycaemia, often due to early insulin resistance and beta-cell dysfunction. It is a pre-diabetic state and carries increased risk of:
- Type 2 diabetes
- Cardiovascular disease
Cheat Sheet (Exam Gold)
- IFG = fasting problem
- IGT = post-meal problem
- Diabetes = either fasting ≥7 OR 2-hr ≥11.1
| Condition | Fasting | 2-hour OGTT |
|---|---|---|
| Normal | <6.1 | <7.8 |
| IFG | 6.1–6.9 | <7.8 |
| IGT | <7.0 | 7.8–11.0 |
| Diabetes | ≥7.0 | ≥11.1 |
🔥 High-yield point:
- IGT = early diabetes marker + CV risk
Flash Cards
Q1: What defines impaired fasting glucose?
A: Fasting glucose 6.1–6.9 mmol/L
Explanation: Reflects hepatic insulin resistance.
Q2: What defines impaired glucose tolerance?
A: 2-hour OGTT 7.8–11.0 mmol/L
Explanation: Indicates postprandial glucose dysregulation.
Q3: Which is a better predictor of cardiovascular risk: IFG or IGT?
A: IGT
Explanation: Postprandial hyperglycaemia is more atherogenic.
Q4: What is the diagnostic fasting glucose for diabetes?
A: ≥ 7.0 mmol/L
Q5: What is the 2-hour OGTT cutoff for diabetes?
A: ≥ 11.1 mmol/L
MCQs (High-Level)
MCQ 1
A patient has fasting glucose 6.5 mmol/L and 2-hour glucose 7.2 mmol/L. What is the diagnosis?
a) Diabetes mellitus
b) Impaired fasting glucose
c) Impaired glucose tolerance
d) Normal glucose tolerance
Answer: b) Impaired fasting glucose
Explanation: Fasting 6.1–6.9 = IFG; 2-hour normal.
MCQ 2
Which of the following is false regarding impaired glucose tolerance?
a) It is defined by abnormal 2-hour OGTT
b) Fasting glucose must be ≥7 mmol/L
c) It increases cardiovascular risk
d) It is a prediabetic state
Answer: b) Fasting glucose must be ≥7 mmol/L
Explanation: Fasting must be <7 in IGT.
MCQ 3
A patient has fasting glucose 7.2 mmol/L and 2-hour glucose 10 mmol/L. Diagnosis?
a) IGT
b) IFG
c) Diabetes mellitus
d) Normal
Answer: c) Diabetes mellitus
Explanation: Fasting ≥7 alone is diagnostic.
MCQ 4
Which condition is most associated with postprandial hyperglycaemia?
a) IFG
b) IGT
c) Type 1 diabetes
d) Reactive hypoglycaemia
Answer: b) IGT
Explanation: IGT reflects impaired post-meal glucose handling.
MCQ 5
A patient has fasting 5.5 mmol/L and 2-hour 7.6 mmol/L. Interpretation?
a) IGT
b) IFG
c) Diabetes
d) Normal
Answer: d) Normal
Explanation: Both values below thresholds.
MCQ 6 (Challenging)
Which abnormality appears earliest in type 2 diabetes pathogenesis?
a) Elevated fasting glucose
b) Elevated HbA1c
c) Postprandial hyperglycaemia
d) Ketoacidosis
Answer: c) Postprandial hyperglycaemia
Explanation: IGT is earliest detectable abnormality.
Summary for Quick Exam Revision
Impaired glucose tolerance is defined by a normal fasting glucose below 7 mmol/L but an elevated 2-hour OGTT value between 7.8 and 11.1 mmol/L, representing postprandial dysglycaemia due to early insulin resistance and beta-cell dysfunction. It is distinct from impaired fasting glucose, where fasting levels are elevated between 6.1 and 6.9 mmol/L but post-load glucose remains normal. Diabetes mellitus is diagnosed when fasting glucose is ≥7 mmol/L or 2-hour OGTT is ≥11.1 mmol/L, or HbA1c ≥6.5%. IGT is clinically important because it is a prediabetic state associated with a significantly increased risk of progression to type 2 diabetes and cardiovascular disease, with postprandial glucose abnormalities being more strongly linked to atherosclerosis. Recognizing the distinction between IFG and IGT is critical in exams and clinical practice, as IGT often appears earlier in disease progression and warrants early lifestyle and pharmacological intervention to prevent long-term complications.