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Glucose Tolerance Test

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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

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Glucose Tolerance Test

  1. 1. Professor (Dr.) Namrata Chhabra Biochemistry for Medics- Lecture notes www.namrata.co 11/05/14 Biochemistry for medics- Lecture notes 1
  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 15. 11/05/14 Biochemistry for medics- Lecture notes 15
  16. 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. 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. 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. 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. 20. Time in minutes Blood glucose (mg/Dl) 11/05/14 20 Biochemistry for medics- Lecture notes
  21. 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. 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. 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. 24. Time in minutes Blood glucose (mg/Dl) 11/05/14 Biochemistry for medics- Lecture notes 24
  25. 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. 26. Hyperthyroidism Pregnancy After gastro-enterostomy Early diabetes mellitus 11/05/14 Biochemistry for medics- Lecture notes 26
  27. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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

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