Glucose tolerance test- Indications, contraindications, preparation of a patient, precautions, types of GTT, normal curve, diabetic curve, renal glycosuria, lag curve, Criteria for diagnosis of DM

1. Professor (Dr.) Namrata Chhabra
Biochemistry for Medics- Lecture notes
www.namrata.co
11/05/14 Biochemistry for medics- Lecture notes 1

2. • The ability to utilize carbohydrates can be
determined by Glucose tolerance test.
• Initially fasting blood glucose is estimated
• A loading dose of glucose is given.
• The blood glucose levels are estimated at
regular intervals after the glucose load
• In conditions of insulin deficiency, blood
glucose levels get elevated due to impaired
utilization of glucose.
11/05/14 Biochemistry for medics- Lecture notes 2

3. A) Decreased Glucose tolerance
Decreased carbohydrate tolerance (non-utilization
of carbohydrate load) is observed
in conditions causing hyperglycemia, for
example:
 Diabetes mellitus
 Hyperactivity of anterior pituitary and
adrenal cortex
 Hyperthyroidism
 Stress
11/05/14 Biochemistry for medics- Lecture notes 3

4. B) Increased Glucose Tolerance
Increased carbohydrate tolerance is observed
in all conditions that cause hypoglycemia-i)
Hypopituitarism
ii) Hyperinsulinism
iii) Hypothyroidism
iv) Adrenal cortical hypofunction
v) Decreased gastro intestinal absorption like
sprue, celiac disease.
11/05/14 Biochemistry for medics- Lecture notes 4

5. i) In asymptomatic persons with sustained or
transient glycosuria
ii) In persons with symptoms of diabetes but no
glycosuria or hyperglycemia
iii) Persons with family history but no
symptoms or positive blood findings
11/05/14 Biochemistry for medics- Lecture notes 5

6. iv)In persons with or without symptoms of
diabetes mellitus showing one abnormal
blood finding
v) In patients with neuropathies or
retinopathies of unknown origin
vi) In women with H/o having delivered large
babies.
11/05/14 Biochemistry for medics- Lecture notes 6

7. a) In proven cases of diabetes mellitus the test
is not required.
b) GTT is required only in doubtful cases, it is
not recommended for follow up of patient.
c) The test should not be carried out in acutely
ill patients
11/05/14 Biochemistry for medics- Lecture notes 7

8. a) The patient is instructed to have good
carbohydrate diet for 3 days prior to the test.
Further , diet containing about 30-50 G of
carbohydrate should be taken on the evening
prior to the test.
b) The patient should avoid drugs likely to
influence the blood glucose levels, for at
least, 2 days prior to the test
11/05/14 Biochemistry for medics- Lecture notes 8

9. c) Patient should abstain from smoking during
the test.
d) Strenuous exercise on the previous day is to
be avoided.
e) The exercise is also to be avoided on the
same day prior to the test
11/05/14 Biochemistry for medics- Lecture notes 9

10. Standard Oral glucose tolerance test
I/V Glucose tolerance test
Mini Glucose tolerance test
11/05/14 Biochemistry for medics- Lecture notes 10

11. a) At about 8 a.m. the fasting blood
and urine samples are collected.
These are called zero samples.
b) A loading dose of 75 g.
anhydrous glucose dissolved in
250-300 ml of water is given to
the patient.
11/05/14 Biochemistry for medics- Lecture notes 11

12. • In children 1.75 g of glucose /kg body weight
is given.
• In the classical procedures, the blood and
urine samples are collected at half hourly
interval of the next two and a half hour or
three hours.
• Glucose is estimated in all the blood
samples.
• Urine is analyzed for the presence of
glucose.
11/05/14 Biochemistry for medics- Lecture notes 12

13. A curve is plotted with the blood glucose
levels on the vertical axis against the time of
collection on the horizontal axis.
The curve so obtained is called glucose
tolerance curve.
11/05/14 Biochemistry for medics- Lecture notes 13

14. Fasting
(Zero
sample)
30
minutes
60
minutes
90
minutes
120
minutes
150
minutes
180
minutes
Blood
Glucose
(mg/dl)
90 100 150 120 110 80 70
Urinary
Glucose
nil nil nil nil nil nil nil
11/05/14 Biochemistry for medics- Lecture notes 14

15. 11/05/14 Biochemistry for medics- Lecture notes 15

16. i) Fasting blood glucose (Zero hour sample)- is
90 mg /dl, which is well within the normal
range(Normal 60-100 mg/dl).
ii) There is rise of blood glucose after glucose
load and the peak value is observed at I hour.
This is due to absorption of glucose from the
intestine.
11/05/14 Biochemistry for medics- Lecture notes 16

17. iii) Insulin is released upon increase of blood
glucose level. There is fall in blood glucose
with time due to glucose utilization promoted
by insulin.
iv) The normal blood glucose level is achieved
after 150 minutes.
11/05/14 Biochemistry for medics- Lecture notes 17

18. 1) Fasting blood glucose is higher than normal
2) The highest value is attained at 1 hour to 1
hour 30 minutes.
3) The highest value exceeds the renal
threshold
4) Glucose is found in almost all the urine
samples.
5) The blood glucose level does not return to
the fasting level even within 2hour 30
minutes.
11/05/14 Biochemistry for medics- Lecture notes 18

19. Fasting
(Zero
sample)
30
minutes
60
minutes
90
minutes
120
minutes
150
minutes
180
minutes
Blood
Glucose
(mg/dl)
200 225 350 300 275 250 225
Urinary
Glucose
+ + + + + + +
11/05/14 Biochemistry for medics- Lecture notes 19

20. Time in minutes Blood glucose (mg/Dl) 11/05/14 20 Biochemistry for medics- Lecture notes

21. Blood glucose levels are within the normal
limits.
Glucose tolerance curve is normal.
There is lowering of renal threshold.
Thus glucose is found in some of the samples
depending upon the renal threshold.
11/05/14 Biochemistry for medics- Lecture notes 21

22. Early diabetes mellitus,
Pregnancy,
Renal disease,
Heavy metal poisoning
Deficiency of carrier protein (SGLT-2).
Renal glycosuria can also be observed in
children of diabetic parents.
11/05/14 Biochemistry for medics- Lecture notes 22

23. Fasting
(Zero
sample)
30
minutes
60
minutes
90
minutes
120
minutes
150
minutes
180
minutes
Blood
Glucose
(mg/dl)
90 130 150 140 120 100 90
Urinary
Glucose
nil + + + + ± nil
11/05/14 Biochemistry for medics- Lecture notes 23

24. Time in minutes Blood glucose (mg/Dl)
11/05/14 Biochemistry for medics- Lecture notes 24

25. Fasting blood glucose is normal.
Sharp rise within 30 minutes to one hour
The blood glucose levels exceed the renal
threshold.
The decline is rapid and the normal levels are
attained back.
 Some of the urine samples contain glucose,
where the blood glucose is above the renal
threshold.
11/05/14 Biochemistry for medics- Lecture notes 25

26. Hyperthyroidism
Pregnancy
After gastro-enterostomy
Early diabetes mellitus
11/05/14 Biochemistry for medics- Lecture notes 26

27. Fasting
(Zero
sample)
30
minutes
60
minutes
90
minutes
120
minutes
150
minutes
180
minutes
Blood
Glucose
(mg/dl)
90 230 180 150 120 100 90
Urinary
Glucose
nil + + nil nil nil nil
11/05/14 Biochemistry for medics- Lecture notes 27

28. •This test is undertaken for patients with
malabsorption (Celiac disease or
enteropathies),
•Under these conditions oral glucose load is not
well absorbed and
• the results of oral glucose tolerance test
become inconclusive.
11/05/14 Biochemistry for medics- Lecture notes 28

29. • I/V glucose tolerance test is carried out by
giving 25 g of glucose dissolved in 100 ml
distilled water as intravenous injection within
5 minutes.
• Completion of infusion is taken as 0 time.
• Blood samples are taken at 10 minutes
interval for the next hour.
• The peak value is reached within a few
minutes and the value touches to near
normal in 45-60 minutes.
11/05/14 Biochemistry for medics- Lecture notes 29

30. Interpretation
• In normal individuals, blood glucose level
returns to normal within 60 minutes
• In diabetes mellitus, decline is slow
• The initial values are attained in 120 minutes.
11/05/14 Biochemistry for medics- Lecture notes 30

31. a) Acute infections- Cortisol is secreted, the
curve is elevated and prolonged
b) Liver diseases- The curve is elevated and
prolonged.
c) Hyperthyroidism- There is steep rise in curve.
11/05/14 Biochemistry for medics- Lecture notes 31

32. d) Hypothyroidism-A flat curve is obtained in
hypothyroidism. Thyroid hormone increases
the absorption of glucose from the gut.
e) Starvation- There is rise of counter
regulatory hormones, which show increased
glucose tolerance
11/05/14 Biochemistry for medics- Lecture notes 32

33. As per current WHO recommendations, in
the mini or modern glucose tolerance test,
only two samples are collected,
 Fasting (zero hour) and 2 hour post glucose
load.
Urine samples are also collected during the
same time.
The diagnosis is made from the variations
observed in these results.
11/05/14 Biochemistry for medics- Lecture notes 33

34. Time of sample
collection
Normal person Criteria for
diagnosing
diabetes mellitus
Criteria for
diagnosing IGT
Fasting
<110 mg/dl
<(6.1m.mol/L)
> 126 mg/dl
>(7.0m.mol/L)
110- 126 mg/dl
2 hour after glucose
load
<140 mg/dl
<(7.8mmol/L)
> 200 mg/dl
140-199 mg/dl
11/05/14 Biochemistry for medics- Lecture notes 34

35. For proper evaluation of the test, the subjects
should be normally active and free from
acute illness.
 Medications that may impair glucose
tolerance include diuretics, contraceptive
drugs, glucocorticoids, niacin, and phenytoin
should be avoided on that day.
11/05/14 Biochemistry for medics- Lecture notes 35

36. Cortisone stress test- used for detecting pre
diabetes or Latent diabetes
Extended GTT- To diagnose the cause of
hypoglycemia especially 2-3 hours after
meals.
11/05/14 Biochemistry for medics- Lecture notes 36

37. If the fasting plasma glucose level is 126
mg/dL or higher on more than one occasion,
further evaluation of the patient with a
glucose challenge is unnecessary. However,
when fasting plasma glucose is less than 126
mg/dL in suspected cases, a standardized oral
glucose tolerance test may be done .
11/05/14 Biochemistry for medics- Lecture notes 37

38. A random plasma glucose concentration
>11.1 mmol/L (200 mg/dL) accompanied by
classic symptoms of DM (polyuria, polydipsia,
weight loss) is sufficient for the diagnosis of
DM.
11/05/14 Biochemistry for medics- Lecture notes 38