Oral Glucose Tolerance Test (OGTT) Overview
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Questions and Answers

List three potential medical conditions that could lead to hypoglycemia.

Hypothyroidism, Addison’s disease, and insulinoma.

Describe the primary method used for estimating serum glucose levels.

The glucose oxidase method is used to estimate serum glucose levels.

What is the significance of preventing glycolysis in blood samples for glucose estimation?

Preventing glycolysis ensures accurate glucose measurements, as glycolysis can decrease serum glucose by 5-7% in one hour.

How does the absorbance of a serum sample relate to its glucose concentration?

<p>The glucose concentration is calculated using the formula: glucose concentration (mg/dL) = (absorbance of sample × concentration of standard) / absorbance of standard.</p> Signup and view all the answers

What precaution should be taken regarding medication before a fasting blood glucose test?

<p>You should avoid medications that can interfere with blood glucose levels, such as corticosteroids and diuretics.</p> Signup and view all the answers

What is the purpose of the Oral Glucose Tolerance Test (OGTT)?

<p>The OGTT checks the body's capacity to utilize a specific amount of glucose and determines how quickly it is cleared from the blood.</p> Signup and view all the answers

List at least three indications for performing an OGTT.

<p>Indications include family history of diabetes, obesity, and unexplained episodes of hypoglycemia.</p> Signup and view all the answers

What should patients avoid three days prior to the OGTT?

<p>Patients should avoid certain medications such as hormones, oral contraceptives, and steroids.</p> Signup and view all the answers

Describe the normal insulin response during an OGTT in a healthy individual.

<p>In a healthy individual, insulin response peaks within 30 to 60 minutes and returns to normal levels within 3 hours.</p> Signup and view all the answers

What is the role of renal glucosuria in relation to OGTT?

<p>Renal glucosuria refers to the excretion of glucose in urine, indicating a possible renal threshold issue that can be assessed during OGTT.</p> Signup and view all the answers

What conditions during pregnancy warrant the performance of an OGTT?

<p>Conditions include transitory glycosuria or hyperglycemia, history of large infants, stillbirths, and premature labor.</p> Signup and view all the answers

How does the OGTT help in diagnosing mild diabetes?

<p>It detects mild diabetes when fasting or random glucose levels are normal by evaluating the glucose utilization capacity.</p> Signup and view all the answers

Why is it important for patients not to restrict carbohydrate intake before an OGTT?

<p>Patients should not restrict carbohydrates to ensure the test accurately reflects their body's glucose handling capability.</p> Signup and view all the answers

What is the main difference between the cause of diabetes mellitus and renal glucosuria?

<p>Diabetes mellitus is caused by a defect in the pancreas, while renal glucosuria is due to a congenital lowering of the renal threshold for glucose.</p> Signup and view all the answers

What is the pediatric dosage of glucose based on body weight and what is the maximum amount allowed?

<p>The pediatric dosage of glucose is calculated at 1.75 g/kg, with a maximum amount of 75 g.</p> Signup and view all the answers

What occurs to blood glucose levels in renal glucosuria compared to diabetes mellitus?

<p>In renal glucosuria, blood glucose levels can be normal or even lowered, whereas in diabetes mellitus, blood glucose levels are typically hyperglycemic.</p> Signup and view all the answers

Why does hyperglycemia occur after a heavy carbohydrate meal?

<p>Hyperglycemia after a heavy carbohydrate meal occurs due to the increased rate of glucose absorption.</p> Signup and view all the answers

Describe the fasting blood glucose levels considered normal.

<p>Normal fasting blood glucose levels range from 70-100 mg%.</p> Signup and view all the answers

What peak blood glucose levels are reached after glucose administration in a normal response?

<p>In a normal response, peak blood glucose levels reach 120-140 mg% after 0.5-1 hour.</p> Signup and view all the answers

What role does adrenaline play in hyperglycemia during stress?

<p>During stress, adrenaline is secreted from the adrenal medulla, leading to an increase in blood glucose levels.</p> Signup and view all the answers

What physiological mechanism causes blood glucose levels to decrease after reaching their peak?

<p>The decrease in blood glucose levels after reaching the peak is due to the release of insulin from the pancreas.</p> Signup and view all the answers

What effect do glucocorticoids have on blood glucose levels in Cushing’s syndrome?

<p>Glucocorticoids act as insulin antagonists, leading to elevated blood glucose levels in Cushing’s syndrome.</p> Signup and view all the answers

At what blood glucose level do symptoms of hypoglycemia typically start to occur?

<p>Symptoms of hypoglycemia typically occur when blood glucose levels drop below 45-75 mg/dL.</p> Signup and view all the answers

What distinguishes the fasting glucose levels of mild diabetes from normal levels?

<p>In mild diabetes, fasting blood glucose levels are between 140-160 mg%, which is higher than normal levels.</p> Signup and view all the answers

How do urine glucose levels differ in mild and severe diabetes?

<p>In mild diabetes, urine shows a '++' level of glucose, while in severe diabetes, it shows '+++.'</p> Signup and view all the answers

How does glucose availability affect brain function under physiological conditions?

<p>The brain relies entirely on blood glucose for energy, and impairment of cerebral function begins when glucose levels fall below 50 mg/dL.</p> Signup and view all the answers

What is renal glucosuria and how does it affect glucose absorption?

<p>Renal glucosuria is a congenital defect that lowers the renal threshold for glucose absorption, leading to glucose loss in urine.</p> Signup and view all the answers

What condition can arise if diabetes mellitus or renal glucosuria is not treated?

<p>Ketosis can occur if diabetes mellitus or renal glucosuria is not treated.</p> Signup and view all the answers

What is the significance of the return to fasting levels after two hours in a normal blood sugar curve?

<p>In a normal blood sugar curve, the return to fasting levels after two hours indicates proper glucose metabolism.</p> Signup and view all the answers

Study Notes

Oral Glucose Tolerance Test (OGTT)

  • OGTT is used to diagnose or confirm suspected diabetes.
  • A random blood glucose greater than 200 mg/dL or a fasting blood glucose greater than 126 mg/dL confirms diabetes.
  • In mild diabetes, with normal fasting or random glucose levels, an OGTT is indicated.
  • The test assesses the body's ability to utilize and clear glucose from the blood.

Definition of OGTT

  • It is a test to assess an individual's capacity for glucose metabolism and how quickly it's cleared from the blood.

Indications for OGTT

  • Detecting mild diabetes in individuals with normal fasting or random glucose levels.
  • Determining the renal threshold for glucose.

When OGTT is indicated

  • Family history of diabetes.
  • Obesity.
  • Unexplained episodes of hypoglycemia.
  • History of recurrent infections (boils, abscesses).
  • Women with a history of large infants, stillbirths, neonatal death, or premature labor.
  • Transient glycosuria or hyperglycemia during pregnancy, surgery, trauma, stress, or myocardial infarction.

Procedure for OGTT

  • Patients should not restrict carbohydrate intake in the days or weeks prior to the test.
  • Medications that may affect the test results (hormones, oral contraceptives, steroids) must be discontinued 3 days before.
  • Insulin and oral hypoglycemic drugs should be withheld until the test is completed. Avoid testing during illness.

Patient preparation and other details

  • The patient's weight is recorded.
  • Pediatric doses of glucose are based on body weight, calculated as 1.75 g/kg, not to exceed 75 g.
  • Pregnant women receive 100 g glucose, nonpregnant adults 75 g glucose.
  • Blood and urine samples are collected every 0.5-1 hour for 2 hours. These samples are analyzed for glucose content.
  • A curve is created plotting blood glucose levels (mg/%) versus time in hours.

Normal Blood Sugar Curve

  • Fasting blood glucose is 70-100 mg/%.
  • Blood glucose gradually increases to a peak during 0.5-1 hour.
  • The peak glucose level is 120-140 mg/%, always below the renal threshold (180 mg/%).
  • Blood glucose gradually decreases back to the fasting level within 2 hours.
  • All urine samples are free of glucose.

Diabetic Blood Sugar Curve

  • Fasting blood glucose levels in mild and severe diabetes range from 140-160mg% and 180-200mg% respectively
  • The peak glucose level in mild diabetes occurs after 1 hour, reaching 200-250 mg/%.
  • Peak glucose levels in severe diabetes occur after 1 hour, ranging from 300-400 mg/%.
  • No return to fasting levels in severe diabetes after 2 hours.
  • Positive for glucose in the urine (++) and (++++).

Renal Glucosuria Curve

  • A congenital defect in renal glucose absorption from the glomerular filtrate causes renal glucosuria.
  • This results in a renal threshold lowering (e.g., 100-110 mg/%) from the normal threshold of 180 mg/%.
  • The pancreas, insulin release, and glucose utilization are normal, but glucosuria occurs due to this lower renal threshold.

Diabetes Mellitus vs. Renal Glucosuria

  • Diabetes Mellitus: Caused by a lack or deficiency of insulin (pancreas issue); characterized by elevated blood glucose (hyperglycemia) and glucose in the urine.
  • Renal Glucosuria: Caused by a congenital defect in renal glucose absorption (kidney issue); characterized by normal or low blood glucose and glucose in the urine.

Serum Glucose Estimation

  • Method: Glucose oxidase method.
  • Sample: Serum or plasma.
  • Principle: Glucose oxidase catalyzes glucose oxidation to gluconic acid and H₂O₂. Peroxidase, phenol, and 4-aminoantipyrine react with H₂O₂ to produce a colored compound.
  • Procedure: Measurement against reagent blank after 10 minute incubation at 37°C or 30 minutes at room temperature.
  • Units: Absorbance is converted to glucose concentration (mg/dL)

Specimen Precautions

  • Avoid prolonged tourniquet application to prevent blood glucose decrease.
  • Glycolysis, which decreases glucose levels, is mitigated by adding sodium fluoride.
  • Rapid sample separation/cooling prevents glycolysis.
  • Fasting tests require no food or drink for eight hours before the test.
  • Note medications that could affect glucose levels (e.g., corticosteroids, diuretics).

Causes of Hyperglycemia

  • Alimentary: After heavy carbohydrate meals, causing temporary hyperglycemia.
  • Diabetic: Hyperglycemia exceeds the renal threshold, leading to glucose excretion in urine due to insulin defects.
  • Adrenaline: Stress-induced adrenaline secretion can lead to hyperglycemia.
  • Cushing's syndrome: Caused by hyperfunction of adrenal cortex.
  • Gigantism/acromegaly: Caused by hyperfunction of the pituitary gland.
  • Gestational: Occurs during pregnancy and disappears after labor.

Hypoglycemia

  • The brain heavily relies on blood glucose for energy.
  • Symptoms of central nervous system dysfunction arise due to low blood glucose.
  • Symptoms often appear when blood glucose reaches 45-75 mg/dL.
  • Cerebral function impairment starts when blood glucose levels are under 50 mg/dL.

Causes of Hypoglycemia

  • Side effects of diabetic medications.
  • Extensive liver disease.
  • Hypothyroidism.
  • Hypopituitarism.
  • Addison's disease.
  • Pancreatic disease/cancer.
  • Insulinoma.

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Description

This quiz explores the Oral Glucose Tolerance Test (OGTT), a critical tool for diagnosing diabetes. It covers definitions, indications, and circumstances when the OGTT is recommended. Understanding this test is essential for recognizing glucose metabolism issues.

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