What is a glucose tolerance test?
The oral glucose tolerance test (glucose tolerance test, also briefly OGTT) used for the detection of impaired glucose utilization and the diagnosis of diabetes mellitus. In overt diabetes mellitus, it is contraindicated.
The oral glucose tolerance test is used in a modified form for the diagnosis of other endocrine disorders (GH suppression test in acromegaly, extended OGTT for up to 6 hours for suspected hypoglycaemia eg insulinoma).
Principle of the method
Idea is to determine the blood glucose control ability of the body with the help of a strong stimulation by recorded sugar. For this purpose, dissolved glucose is used because it is the form of sugar that can receive the fastest of the body and leads to a sharp rise in blood glucose concentration (equivalent to determining a system response in systems theory) in water. Stimulated by this increase in blood sugar, the pancreas regulates the secretion of insulin against which stimulates hypoglycemic reactions in the liver, muscle and fat cells. During the OGTT is periodically over time of the blood glucose level, possibly insulin, as measured: fasting value increase, maximum and drop in blood sugar except for fasting value.
With an OGTT regulating ability of the body in strength and the speed can be determined, which allows diagnostic statements with appropriate benchmarks. For example, in a delayed decrease in fasting glucose levels are closed on insulin resistance or reduced Insulinsekretionsfähigkeit, while warmer maximum glucose values or failure to achieve a fasting glucose level within a defined period of time, to the noticeable diabetes mellitus.
Indication as a diagnostic method
The WHO recommends OGTT generally as a diagnostic tool, also contrary to concerns regarding effort and cost. This is explained by the poor sensitivity of a pure fasting glucose determination; According cited DECODE study about 30% of diabetics are thus not detected. Also could be discovered only through a oGTT impaired glucose tolerance (IGT).
The German Diabetes Association (DDG) proposed in the 2007 Directive kürzerintervalliges screening with an OGTT if the following risk factors:
-Type 2 diabetes mellitus in first-degree relatives
-Obesity and physical inactivity
-Arterial hypertension (blood pressure ≥ 140/90 mmHg)
-Dyslipoproteinemia with HDL-cholesterol ≤ 35 mg / dL and / or triglycerides ≥ 250 mg / dl
-State after gestational diabetes or having a baby with birth weight> 4000 g
-Earlier detection of impaired glucose tolerance (IGT) or impaired fasting glucose (IGF)
-Macrovascular disease
-Albuminuria
It should also be noted that the HbA1c or fructosamine value are unsuitable for a diabetes screening.
Contraindications
Contraindications to the OGTT are according to the DDG intercurrent illness (eg after gastrointestinal resections or gastrointestinal disorders with altered absorption) or an already manifested diabetes mellitus