- OGTT
- Oral glucose tolerance test
- Standard oral tolerance test
- Standard gestational screen
- GTT
- Glucose tolerance test
- Glucose challenge test
- Gestational diabetes screening
- Grey top tube
- Red, tiger, or green top tube also acceptable
- 5 mL of venous blood collected as:
- Full OGTT Protocol
- 1st sample - Fasting baseline immediately before ingestion of glucose drink
- 2nd sample - 30 minutes after glucose ingestion
- 3rd sample - 1 hour after glucose ingestion
- 4th sample - 2 hours after glucose ingestion
- 5th sample - 3 hours after glucose ingestion
- Glucose challenge test (Gestational)
- 1st sample - Fasting baseline immediately before ingestion of glucose drink
- 2nd sample - 1 hour after glucose ingestion
Additional information (WHO guidelines)
- The most common protocol is the screening protocol with an initial blood glucose then repeat at 2 hours
- For OGTT: Anhydrous glucose is dissolved in 250 mL water (flavored with sugar-free lemon / glucola drink for better palatability)
- Adults: 75 g glucose
- Pregnant women: 100 g glucose
- Possible gestational diabetes: 100 g glucose
- Children 1.75 g/kg, up to 75 g
- For Glucose challenge test (Gestational)
- 50 g glucose
- Fasting for 12-16 hrs before test
- The patient should eat a diet of >150 g of carbohydrates for 3 days before the test
- Avoid smoking, coffee, alcohol, or strenuous exercise for 8 hrs before or during test
- Ensure any drug that affects glucose levels are discontinued 3 days before the test
- The patient should remain quiet/relaxed throughout the test
- Record the patient's weight and the time of collection on lab request
- OGTT is a timed test that measures glucose levels in the blood after administration of an oral glucose challenge
- This test is commonly performed as a screening test for gestational diabetes, glucose intolerance or metabolic syndrome
- In healthy individuals, the insulin response to a large oral glucose dose is seen as a peak in serum/plasma glucose levels after 30-60 mins, and return to normal within 3 hrs since sufficient insulin is present to metabolize the ingested glucose
- OGTT is only performed in individuals who are capable of oral consumption
- The OGTT is indicated in the following conditions:
- As a confirmatory test for diabetes mellitus (significantly replaced by the HgbA1C test, but is still the “gold standard”)
- As a diagnostic aid in hypoglycemia and malabsorption syndrome
- Family history of diabetes
- Obesity (Screening for metabolic syndrome)
- In women with a history of
- Delivery of large infants
- Stillbirths
- Neonatal death
- Premature labor
- Spontaneous abortions
- Abnormal previous glucose tolerance test
- Transitory glycosuria or hyperglycemia detected during
- Pregnancy
- Surgery
- Trauma
- Stress
- Myocardial infarction (MI)
- ACTH administration
- When urine sugar is detected or when the fasting blood sugar level is elevated
- Identify abnormal renal tubular function if glycosuria occurs without hyperglycemia
- OGTT is contraindicated or postponed in the following conditions:
- Persistent fasting hyperglycemia >140 mg/dL or >7.8 mmol/L
- Patients with overt diabetes mellitus
- Persistent 2-hour post glucose ingestion level of glucose >200 mg/dL (>11.1 mmol/L)
- Recent history of surgery, myocardial infarction, or labor and delivery. 2 wks of recovery should be allowed before performing the test
- Common illness such as flu or a severe cold
- The diagnostic criteria for diabetes mellitus is based on the following:
- Blood glucose results (>2 tests must be met or exceeded)
- Fasting: >95 mg/dL (>5.3 mmol/L)
- 1-hr: >180 mg/dL (>10.8 mmol/L)
- 2-hr: >155 mg/dL (>8.6 mmol/L)
- 3-hr: >140 mg/dL (>7.8 mmol/L)
- All pregnant women should be tested for gestational diabetes with a Glucose Challenge Test (GCT) using 50-g dose of glucose at 24-28 wks of gestation. Abnormal GCT should be followed with an OGTT for confirmation, and abnormal OGTT results during pregnancy mandate a repeat OGTT at the first postpartum visit
- During labor, maintain maternal glucose levels at 80-100 mg/dL (4.4-5.5 mmol/L); be cautious of markedly increased insulin sensitivity in the immediate postpartum period
- Hypoglycemia may clinically present as:
- Headache
- Hunger
- Confusion and nervousness
- Coma
- Focal or diffuse neurologic deficits
- Irritability and restlessness
- Sweating
- Weakness
- Hyperglycemia may clinically present as:
- Abdominal pain
- Blurry vision
- Fatigue
- Muscle cramps
- Nausea and vomiting
- Polyuria and thirst
- Tachypnea
- Weight loss
- The risk factors for developing gestational diabetes include:
- Age over 35 years
- Obesity
- Women of Aboriginal, Hispanic, South Asian, Asian or African descent
- Gestational diabetes in a previous pregnancy
- Previous baby weighing over 9 pounds
- Unexplained death in a previous fetus or newborn
- Congenital malformation in a previous child
- History of polycystic ovary syndrome
- Hirsutism
- Acanthosis nigricans
- Criteria for abnormal result on 100-g, three-hour oral glucose tolerance tests in pregnant women
Blood sample National Diabetes Data Group Carpenter and Coustan Fasting 105 mg/dL (5.8 mmol/L) 95 mg/dL (5.3 mmol/L) 1-hour 190 mg/dL (10.5 mmol/L) 180 mg/dL (10.0 mmol/L) 2-hour 165 mg/dL (9.2 mmol/L) 155 mg/dL (8.6 mmol/L) 3-hour 145 mg/dL (8.0 mmol/L) 140 mg/dL (7.8 mmol/L)
Gestational diabetes mellitus is diagnosed if two or more of the values (venous serum or plasma glucose levels) are met or exceeded
Additional information
- If the person undergoing OGTT vomits the glucose solution, the test is declared invalid and can be repeated after 3 days
- Glucose levels normally tend to increase with age
- The OGTT is of limited diagnostic value for children
- Plasma glucose values are 10-20% higher than serum values
- Factors interfering with the test results include:
- Altered diets as in weight reduction before testing can diminish carbohydrate tolerance and may falsely suggest diabetes
- Prolonged oral contraceptive use can cause elevated glucose levels in the 2nd hr or in later blood specimens
- Impaired physical activity can lead to falsely increased values
- Drugs (listed in high and low result sections)
- Related laboratory tests include:
- B-HCG testing
- Blood glucose
- Blood urea nitrogen (BUN)
- Cholesterol (total and HDL)
- C-peptide
- Creatinine
- Fructosamine
- Hgb A1C
- Insulin
- Ketones
- Microalbumin
- Urinalysis
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
OGTT Test (Not pregnant)
| Conv. Units (mg/dL) | Normal | Impaired Glucose Tolerance | Diabetes |
|---|---|---|---|
| Fasting | <110 | 110-125 |  126 |
| 30 minutes PG* | <170 | ||
| 1 hour PG* |  180 | 181-199 | 200 |
| 2 hours PG* | <140 | 140-199 | 200 |
| 3 hours PG* | <120 | 120-144 | 145 |
| PG = Post ingestion of glucose drink | |||
| SI Units (mmol/L) | Normal | Impaired Glucose Tolerance | Diabetes |
|---|---|---|---|
| Fasting | <6.1 | 6.1-6.9 | 7.0 |
| 30 minutes PG* | <9.4 | ||
| 1 hour PG* | 10.0 | 10.1-11.0 | 11.1 |
| 2 hours PG* | <7.8 | 7.8-11.0 | 11.1 |
| 3 hours PG* | <6.7 | 6.7-8.0 | 8.1 |
| PG = Post ingestion of glucose drink | |||
GCT
| Conv. Units (mg/dL) | SI Units (mmol/L) | |
|---|---|---|
| Fasting | 95 | 5.3 |
| 1 hour PG* | 140 | 7.8 |
PG = Post ingestion of 50 grams glucose drink An abnormal GCT should be followed by a full OGTT
OGTT Test (Pregnant)
| Conv. Units (mg/dL) | SI (mmol/L) | |
|---|---|---|
| Fasting | 95 | 5.3 |
| 1 hour PG* | 180 | 10 |
| 2 hours PG* | 155 | 8.6 |
| 3 hours PG* | 140 | 7.8 |
PG = Post ingestion of 100 gram glucose drink
- Some laboratories use a 75 gram glucose load (in that protocol the 3 hour sample is not drawn)
- Two or more values being abnormally elevated = Gestational diabetes
Conditions associated with elevated levels of glucose, on tolerance testing (e.g. impaired glucose tolerance) include:
- Increased absorption of glucos
- Excess glucose ingestion
- Gastrectomy
- Gastroenterostomy
- Vagotomy
- Hyperthyroidism
- Decreased glucose utilizatio
- Diabetes mellitus
- Hyperlipidemia types III, IV, and V
- Hemochromatosis
- Cushing's disease
- CNS lesions
- Drugs and substances
- Beclomethasone
- Calcitonin
- Cannabis
- Catecholamines
- Chlorpromazine
- Cimetidine
- Corticosteroids
- Corticotropin
- Danazol
- Deflazacort
- Diapamide
- Diazoxide
- Diethylstilbestrol
- Epinephrine
- Estropipate
- Ethacrynic acid
- Felodipine
- Fludrocortisone
- Foscarnet
- Furosemide
- Glucagon
- Heroin
- Human growth hormone
- Imipramine
- Interferon alfa-2a
- Iron
- Levonorgestrel
- Lithium
- Medroxyprogesterone
- Mefenamic acid
- Mephenytoin
- Mestranol
- Methadone
- Methandrostenolone
- Muzolimine
- Naproxen
- Niacin
- Niacinamide
- Nicotinic acid
- Nitrofurantoin
- Norethindrone
- Norethynodrel
- Octreotide
- Oral contraceptives
- Paramethasone
- Perphenazine
- Phenolphthalein
- Phenothiazine
- Phenytoin
- Promethazine
- Quinethazone
- Spironolactone
- Streptozocin
- Thiazides
- Triamterene
- Verapamil
Conditions associated with impaired glucose tolerance (decreased glycogenesis; with hypoglycemia) include:
- Infections
- Severe liver damage
- Pheochromocytoma
- von Gierke's disease
- Pregnancy
- Stress
- Smoking
- Excessive physical activity
Conditions associated with decreased levels of glucose, on tolerance testing (e.g. flat curve, glucose decreased to hypoglycemic levels) include:
- Decreased absorption of glucos
- Sprue
- Celiac disease
- Whipple's disease
- Hypoparathyroidism
- Addison's disease
- Liver disease
- Hypopituitarism
- Hypothyroidism
- Increased insulin secretion
- Pancreatic islet cell hyperplasia or tumor
- Drugs and substance
- Acarbose
- Acetylsalicylic acid
- Beta blockers
- Caffeine
- Chlorpropamide
- Clofibrate
- Fenfluramine
- Fluoxymesterone
- Glimepiride
- Glipizide
- Glyburide
- Guanethidine
- Insulin
- Lisinopril
- MAO inhibitors
- Metformin
- Nandrolone
- Nateglinide
- Niceritrol
- Nitrendipine
- Norethindrone
- Norethisterone
- Oral hypoglycemics
- Pargyline
- Phenformin
- Phenobarbital
- Pioglitazone
- Prazosin
- Repaglinide
- Rosiglitazone
- Sulfonylureas
- Terazosin
- Tolazamide
- Tolbutamide
- Troglitazone
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- Lee KM et al. Evaluation of glucose tolerance in cystic fibrosis: Comparison of 50-g and 75-g tests. J Cyst Fibros. 2006 Dec 8; [Epub ahead of print].
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