ORAL GLUCOSE TOLERANCE TEST

ORAL GLUCOSE TOLERANCE TEST

            Early stages of glucose in tolerance (prediabetics) are not only prerunners of diabetes but also carry high risk of cardiovascular disease. IGT occurs at a much younger age in Indians and are predisposed to get diabetes more or less a decade.

            Early recognition is extreme importance in initiating early interventions to stop the onset of diabetes related complications. Prediabetes is diagnosed with one of the blood tests – a fasting plasma glucose test or a two hour OGTT.

            The fasting plasma glucose test requires an 8 hr fast (no food or drink except water) after which a blood draw is performed. It is usually done in the morning for an OGTT, a patient is given a drink of 75gm of glucose, and a blood draw is taken 2 hrs later. The following laboratory values are the ADA practice guidelines for diagnose the prediabetics and diabetes.

Classification of Glucose Tolerance State

State	FPG Level (mg/dl)	2hrs plasma glucose in OGTT (mg/dl)
IFG	100-125	<200
Isolated IFG	100-125	<140
IGT	<126	140-199
Isolated IGT	<100	140-199
Combined IFG/IGT	100-125	140-199
NGT	<100	<140

Standard 75g of oral glucose

1. An OGTT plasma glucose value between 140-199mg/dl at 2hrs post glucose load (including IGT)
2. The ADA recommends that men and women age 45 and older, especially there that are over weight (i.e. BMI of ³ 25 or higher) be screened for prediabetes.
3. Screening should also be considered in individuals younger than 45, if they are overweight and have one or more additional risk factors.
4. If testing is positive for prediabetes, a follow up test should be performed on a subsequent day to confirm the diagnosis.
5. People with diagnose prediabetes should received regular retesting every one to two years to monitor for type II diabetes. Individuals with a normal screening result can be retested every 3 years. Symptoms of diabetes and causal plasma glucose concentration ³ 200mg/dl

Criteria for diagnosis of diabetes

1. FPG < 100mg/dl = Normal fasting glucose
2. FPG < 100-125mg/dl = Impaired fasting glucose 
3. FPG ³ 126mg/dl = Provisional diagnosis of diabetes
4. 2 hr PG < 140mg/dl  = Normal glucose tolerance test
5. 2 hr PG 140 – 199 mg/dl = Impaired glucose tolerance
6. 2 hr PG >200mg/dl = Provisional diagnosis of diabetes

            In the absence of unequivocal hyperglycemia, diagnosis of diabetes must be confirmed on subsequent day, by measurement of FPG, 2 hr PG or random plasma glucose (if symptoms are present). The FPG test is greatly preferred because of ease of administration, convenience, acceptability to patients, and lower cost. Fasting is defined as no calorie intake for at least 8 hr. This test requires the use of a glucose load containing the equivalent of 75g anydrous glucose dissolved in water. The glucose load fixed at 75g anhydrous glucose or its equivalent for adults of all ages and body weight 1.75g/kg for children upto maximum of 75g. 2 hr PG, 2 hr p post load glucose. Patient with IFG and IGT are now preferred to as having prediabetic indicating the relatively high risk for development of diabetes in these patients. In the absence of pregnancy, IFG and IGT are not clinical entities in their own right but rather risk factors for future diabetes as well as cardiovascular disease. They can be observed as intermediate stages in any of the disease processes. IFG and IGT are associated with metabolic syndrome which includes obesity (especially abdominal / visceral obesity) dyslipidimia of high TG and low HDL type and hypertension.

            It is worth mentioning that MNT aimed at producing 5-10% loss of body weight, exercise and certain pharmalogical agents have variably demonstrated to prevent or delay the development diabetics in people with IGT. Note that many individuals with IGT are euglycemic in their daily lives. Individuals with IFG or IGT may have normal or near normal glycated hemoglobin levels. Individuals with IGT often manifest hyperglycemia only when challenged with oral glucose load used in the standard OGTT.

Note:

            Prediabetes and metabolic syndrome are extremely prevalent, people with prediabetes and metabolic syndrome are at high risk for diabetes and CVD; early detection of IFG / IGT in high risk individuals and interventions to prevent progression to diabetes through intensive lifestyle changes are effective and should be encouraged and effective pharmacologic therapies must also be identified. OGTT utilized as a gold standard for diagnosis of early diabetes. Higher risk levels IGT – macrovascular complications, higher relatives risk for CVD with 2 hr PG hyperglycemia. Screening for diabetes, IGT has raised the need of early detection of prediabetic state IFG and IGT.

1. Persons >45 years
2. Those with central obesity
3. Subjects with micro vascular, coronary, cerebral, peripheral diseases
4. Vascular disease
5. Cases of dyslipidemia, hypertension
6. Women with history of GDM or with birth of large babies
7. Subject with PCOD

REFERENCE:

            Clinical Practice Recommendation, ADA