Hypoglycemia, or abnormally low glucose (blood sugar), occurs occasionally in almost all people with diabetes. To diagnose a hypoglycemic episode, people with diabetes can perform glucose monitoring. This self-testing of glucose levels usually involves pricking the finger or arm for a sample of blood and placing that sample on a test strip. The strip is then analyzed by a glucose meter. The meter digitally displays the glucose level as a number in milligrams per deciliter (mg/dL).

Physicians may use the term Whipple triad in diagnosing hypoglycemia. This refers to:

• Hypoglycemic symptoms
  
  
• Evidence of hypoglycemia from a glucose test (and sometimes also with a c-peptide test and a blood test of insulin)
  
  
• Resolution of symptoms when the level of glucose in the bloodstream returns to normal

The oral glucose tolerance test (OGTT) has been used to diagnose hypoglycemia, most often of the type known as reactive hypoglycemia. However, this glucose test is not used often because the test itself can trigger hypoglycemic symptoms. Glucose monitoring probably remains the most reliable means for measuring day-to-day glucose control and diagnosing hypoglycemia.

For difficult-to-detect hypoglycemia, a physician may recommend that a diabetic patient wear a continuous glucose sensor for three days to record blood sugar levels automatically every 20 minutes. Later, the physician can analyze the data to determine if low glucose levels are occurring at particular times of the 24-hour day, including during sleep.

A low blood glucose reading is any reading below a patient’s physician-recommended target range. An occasionally low glucose reading is generally not a serious issue, but patients should discuss low readings with their physician, especially if readings are frequently or unusually low.