Glucose Tolerance Test

A medical test to determine the ability of an individual to maintain HOMEOSTASIS of Blood Glucose

The most commonly performed version of the Test (OGTT)

HistoryFirst described in 1923 by jerome W.conn(1907-

1994) (Conn syndrome )

GDM

International Association of Diabetes and pregnancy

study groups (IADPSG) criteria American diabetes association(ADA)-2014

Screening for and diagnosis of GDM“One-step” (IADPSG consensus)• Perform a 75-g OGTT, with plasma glucosemeasurement fasting and at 1 and 2 h,at 24–28 weeks of gestation in womennot previously diagnosed with overtdiabetes.• The OGTT should be performed in themorning after an overnight fast of atleast 8 h.

The diagnosis of GDM is made when any ofthe following plasma glucose values areexceeded:Fasting: ≥92 mg/dL (5.1 mmol/L)1 h: ≥180 mg/dL (10.0 mmol/L)2 h: ≥153 mg/dL (8.5 mmol/L)

“Two-step” (NIH consensus)• Perform a 50-g GLT (nonfasting), withplasma glucose measurement at 1 h(Step 1), at 24–28 weeks of gestation inwomen not previously diagnosed withovert diabetes.• If the plasma glucose level measured 1 hafter the load is ≥140 mg/dL* (10.0 mmol/L), proceed to 100-gOGTT (Step 2).

The 100-g OGTT should be performedwhen the patient is fasting.The diagnosis of GDM is made when theplasma glucose level measured 3 h afterthe test is ≥140 mg/dL (7.8 mmol/L).*The American College of Obstetricians andGynecologists (ACOG) recommends a lowerthreshold of 135 mg/dL in high-risk ethnicminorities with higher prevalence of GDM.

OGTT is not an appropriate study for evaluating a

patient suspected of having hypoglycemia.

An OGTT is rarely necessary for the diagnosis of diabetes mellitus.

Recommendation for postpartum care in women with GDM to ruled out prediabetes or overt diabetes

2-hour,75g OGTT 6 to 12 weeks after delivery (nonpregnant OGTT criteria 2h ≥200mg/dl)

Two-hour PG ≥200 mg/dL (11.1 mmol/L)during an OGTT. The test should beperformed as described by the WHO,using a glucose load containing theequivalent of 75 g anhydrous glucosedissolved in water

*In the absence of unequivocalhyperglycemia, result should be confirmedby repeat testing..

Categories of increased riskfor diabetes (prediabetes)FPG 100 mg/dL (5.6mmol/L) to 125 mg/dL

(6.9 mmol/L( )IFG)OR

2-h PG in the 75-g OGTT 140 mg/dL(7.8 mmol/L )to 199 mg/dL

(11.0 mmol/L( )IGT)ORA1C 5.7–6.4%

The Following conditions should be met before an OGTT is performed:

Discontinue , when possible , medications Known to affect glucose tolerance

Perforrm in the morning after 3 days of unrestricted diet & activity (diet containing at least 150g of carbohydrate per day )

After a 10 to 16 hour fast only in ambulatory outpatient (bed rest impairs glucose tolerance) (8-14hour)

• Patient should remain seated during the test without smoking cigarettes

• Testing should use plasma glucose analyzed at a laboratory, not capillary blood glucose analyzed with a blood glucose meter

• GTT should not be performed on hospitalized, acutely ill or inactive patient

• The Test should begin between 7AM and 9AM.• 75g anhydrous glucose/300ml water ingested

over 5minutes

Factors Other Than Diabetes ThatInfluence the Oral Glucose Tolerance Test

Patient PreparationDuration of fastPrior carbohydrate intakeMedications (e.g., thiazides, oral contraceptives,corticosteroids)

TraumaIntercurrent illnessAgeActivityWeight

Administration of GlucoseForm of glucose (anhydrous or monohydrate)Quantity of glucose ingestedVolume in which administeredRate of ingestion

During the TestPostureAnxietyCaffeineSmokingActivityTime of daySample preservation

OGTT Indications 1- Diagnosis of GDM2- Diagnosis of IGT (controversial ) 3- Evalution of a patient with unexplained

nephropathy , neuropathy or retinopathy with random PG <140 mg/dl

4- Population studies for epidemiologic data