An increasingly popular method for measuring blood glucose is to sample capillary or finger-prick blood, which is less History · Testing · Results · Sample method. General. The patient should be on a high carbohydrate diet for three days prior to testing. The patient must be fasting and remain so during the entire test period. The Glucose Tolerance Test (GTT) also referred to as the Oral Glucose Tolerance Test (OGTT), is a method which can help to diagnose instances of diabetes.