Hyperglycemia induced through the ingestion of 75 grams of glucose is used to diagnose diabetes (time 0 and 120 minutes) including gestational diabetes (time 0, 60 and 120). The test is sometimes extended to 5 hours (time 180, 240 and 300) to diagnose other conditions such as reactive hypoglycemia or hypoglycemia due to an insulinoma (insulin-producing tumour) or insulin resistance. Hyperglycemia is sometimes accompanied by tests for insulin, C peptide or growth hormones at each collection time (sometimes including a time 30 minutes).
In reactive hypoglycemia, glucose levels will be below normal and, more specifically (severe hypoglycemia), below 2.2 mmol/L between 2 and 5 hours after glucose ingestion. These low glucose levels should normally be accompanied by symptoms typical of hypoglycemia (nervousness, sweating, shakiness, urgent hunger, etc.). With insulinoma, the fasting blood sugar could also be very low.