Diabetes Basics: A1c versus Time in Range
Diabetes Health Staff
Almost every person who has diabetes knows that the HbA1c (hemoglobin A1c) test is one of the best tools available for tracking your overall blood sugar level for the last 90 days. For example, one person may register a blood glucose level of 8.2 mg/dL at the start of January but then undertakes a serious exercise and meals routine that leads to an A1c reading in April of 7.1 mg/dL. While that result can be very gratifying, it still leads to an unanswered question: How much did that person’s blood sugar levels vary over those three months? Is there is a way to see a pattern of rising and falling levels over that 90-day range?
The answer is yes, thanks to the recent introduction of the Time in Range theory. The significance of this new measurement is to look at how long your blood sugar stays within a specific range, while the A1c provides you with the average blood sugar for the last 90 days.
The range that your blood sugars should be in is something you and your doctor will decide on together. Once you have determined that range, your goal is to maintain it at least 17 out of 24 hours each day. You track this when wearing a CGM that gives you data, glucose trends 24 hours a day. The ADA recommends maintaining your targeted blood sugars 70 % of the time. If you and your doctor decide that your range falls between 70 to 180 mg/dL, then 70% of the Time—17 of the 24 hours—your blood sugars should not be higher or lower than that range.
Let’s say there are two people with diabetes whose A1c’s are identical 7.2 mg/dL. But when both look at their Time in Range readings, the results are dramatically different. The results show that the first person’s Blood sugar levels remained for the most time within an ideal range, with periodic and minor dips into hypoglycemic and then leaps into hyperglycemic numbers. But the second person’s numbers show extensive time spent in the hypoglycemic and hyperglycemic territory. Those opposite numbers average out to 7.2—a deceptive number that makes person number two look in control rather than careening between possibly dangerous states.
Knowing how long your blood sugar stays at a particular range can help fine-tune your therapy and or medication, allowing you to experience fewer highs and lows in your daily self-care care.