Random Plasma Glucose Test
Blood is drawn at any time of day, regardless of whether the patient has eaten. A random plasma glucose concentration of 200 mg/dl (11.1 mmol/l) or higher in the presence of symptoms indicates diabetes.
Oral Glucose Tolerance Test (OGTT)
Blood samples are taken both before and several times after a patient drinks 75 grams of a glucose-based beverage.
Procedure for OGTT
The patient should have been fasting for the previous 8-14 hours (water is allowed).
Usually the OGTT is scheduled to begin in the morning (0700-0800) as glucose tolerance exhibits a diurnal rhythm with a significant decrease in the afternoon. A zero time (baseline) blood sample is drawn.
The patient is then given a glucose solution to drink. The standard dose is 1.75 grams of glucose per kilogram of body weight, to a maximum dose of 75 g. It should be drunk within 5 minutes.
Blood is drawn at intervals for measurement of glucose (blood sugar), and sometimes insulin levels. The intervals and number of samples vary according to the purpose of the test. For simple diabetes screening, the most important sample is the 2 hour sample and the 0 and 2 hour samples may be the only ones collected.
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1999 WHO Diabetes criteria - Interpretation of Oral Glucose Tolerance Test
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Glucose levels
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NORMAL
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Impaired Fasting Glycaemia
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Impaired Glucose Tolerance
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Diabetes Mellitus
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(I.F.G.)
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(I.G.T.)
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(D.M.)
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Venous Plasma
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Fasting
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2hrs
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Fasting
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2hrs
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Fasting
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2hrs
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Fasting
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2hrs
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(mg/dl)
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<110
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<140
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>110 & <126
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<140
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<126
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>140
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>126
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>200
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*FPG = fasting plasma glucose; 2-hour PG = 2-hour plasma glucose concentration during a standard oral glucose (75 gram) tolerance test
