The document describes the glucose tolerance test (GTT) used to evaluate tolerance to glucose loads and diagnose prediabetes and diabetes. It provides instructions for administering the GTT, criteria for diagnosing prediabetes and diabetes based on fasting blood glucose and 2-hour post-load glucose levels, and interpretations of normal, abnormal, diabetic, and other abnormal GTT curves. It also includes 5 case studies presenting GTT values and interpreting the results as normal, prediabetes, diabetes, renal glycosuria, or diabetic ketoacidosis.

1. GTT
Test to evaluate the degree of tolerance of
an individual to a glucose load .
In a normal individual our body has the
ability to absorb glucose and metabolize it
by secreting adequate insulin.

2. Test Preparation/ Instructions:
• Should consume a mixed diet with at least 150 g of
carbohydrate on the 3 days prior to oral glucose
tolerance testing.
• The patient should arrive fasting for a minimum of
eight hours before the test.
• The fasting sample should be taken and the time
point should be notated.
• The patient should then consume the correct
amount of glucose (75 grams) over a maximum of a
5-minute period.

3. Criteria for Diagnosing Diabetes Mellitus:

4. Criteria for Diagnosing Prediabetes:

5. Normal
Person
Prediabetes
Person
Diabetes
Person
Fasting < 100 mg/dL 100 - 125 mg/dL > 126 mg/dL
1 hour < 200 mg/dL
2 hour < 140 mg/dL 140 - 199 mg/dL > 200 mg/dL
Interpretation of OGTT:

6. NORMAL CURVE
• The fasting level is within the normal limits.
• The peak value is reached at 1 hour and it is
below the renal threshold level and returns to
the fasting levels by 2 hours.
• All urine samples are negative for presence of
glucose.

8. Clinical interpretation for ABNORMAL
GTT curve
• Impaired glucose tolerance test
• Fasting level is between 100-126 mg/dl.
• Peak value will be more than the renal threshold value
and the 2 hours value remains between 140-200 mg/dl.
• Traces of glycosuria at the peak and 2 hours samples.

9. Diabetes mellitus curve
• The fasting levels are more than 126 mg/dl.
• The level steadily rises and reaches a peak at 1 hr
and gradually decreases , but the 2 hour level will
be > 200 mg%
• Glycosuria will be present in all the samples.

10. Alimentary glycosuria:
• The GTT curve is normal except an abnormal high
level of blood glucose at the peak 1 hour.
• Glycosuria is present at this time.
• The fasting glucose level and 2 hour glucose level is
within the normal limits. This is called Lag curve.
• This is due to rapid glucose absorption followed by a
burst of insulin production which over-compensates,
resulting in hypoglycaemia.

11. Renal glycosuria Curve
• Normal renal threshold value is 180 mg/dl.
• If the blood sugar level rises above this it appears in
urine.
• Normally increased blood glucose is reflected in urine.
• But when the renal threshold is lowered, glucose gets
excreted in urine..and blood glucose level remains
normal
• NORMALLY SEEN IN RENAL TUBULAR DEFECTS.

12. CASE STUDY 1
• These are the values of oral glucose tolerance test.
Glucose oxidase method ) performed on an
individual.What is your interpretation?
Fasting ½ hr 1 hr 1 ½ hr 2 hr
Blood glucose
(mg/dl)
70 110 140 120 75
Urine sugar
NIL NIL NIL NIL NIL

13. CASE STUDY 2
These are the values of oral glucose tolerance
test. Glucose oxidase method ) performed on an
individual.
What is your interpretation?
Fasting ½ hr 1 hr 1 ½ hr 2 hr
Blood
glucose
(mg/dl)
110 185 230 195 165
Urine sugar
NIL + +++ ++ TRACE

14. Explanation
• Ans: Moderate Diabetes mellitus (Prediabetes)
DIAGNOSTIC CRITERIA
• If fasting plasma sugar is> 126mg/dl.
• If 2-hr post glucose load is > 200 mg/dl.
• If both fasting and 2-hr values are above this.
• If random blood sugar level is > 200mg/dl.

15. CASE STUDY 3
• These are the values of oral glucose tolerance
• test. Glucose oxidase method ) performed on an
individual. What is your interpretation?
Fasting ½ hr 1 hr 1 ½ hr 2 hr
Blood glucose
(mg/dl)
70 105 150 110 75
Urine sugar
NIL + + NIL NIL

16. • RENAL GLYCOSURIA
• DIAGNOSTIC CRITERIA
• Glucose gets excreted in urine.
• Blood glucose level remains normal.

17. CASE STUDY 4
• These are the values of oral glucose tolerance test. Glucose
oxidase method ) performed on an individual.What is your
interpretation?
FASTING ½ HR 1 HR 1 ½ HR 2 HR
BLOOD
GLUCOSE
90 160 200 140 92
URINE
SUGAR
NIL NIL + NIL NIL

18. Explanation
Ans : Alimentary Glucosuria
DIAGNOSTIC CRITERIA
• Fasting and 2-hrs values are normal
• An exaggerated rise in glucose level following
ingestion of glucose.
Causes
• Increased rate of absorption of glucose from
intestine.
• Seen in hyperthyroidism and in patients after
gastrectomy.

19. CASE STUDY 5
• These are the values of oral glucose tolerance test.
Glucose oxidase method ) performed on an
individual.What is your interpretation?
Fasting ½ hr 1 hr 1 ½ hr 2 hr
Blood glucose
(mg/dl)
210 290 360 400 450
Urine sugar
+ ++ +++ +++ ++++
Urine acetone
nil nil + + +

20. Explanation
• Ans : Diabetic ketoacidosis.
• DIAGNOSTIC CRITERIA
• HYPERGLYCEIMIA – SEVERE DM
• GLYCOSURIA
• KETOACIDOSIS
• ACIDOSIS
• HYPERKALAEMIA

21. OTHER INVESTIGATIONS DONE TO MONITOR CONTROL IN
PATIENTS WITH DIABETES MELLITUS
Glycated haemoglobin (HbA1c)
• Normal level 4 - 6% of total Hb
• Indicator of control over the preceding 8 - 12
weeks
Fructosamine
• Glycation of serum protein (esp albumin)
• Normal level 1.5 - 2.4 mmol/L
(when albumin = 5 gm/dL)
• Indicator of control over the preceding 2-3 weeks