Glycated hemoglobin or HbA1c or A1c is widely recognized as the metric
of choice to determine glucose control in both clinical trials and practices for many years till now
and the primary endpoint of many CGM studies too. HbA1c has many limitations that paved the way for
the identification of “Time-in-range” (TIR) as a new metric at the ATTD International Consensus
Conference in Feb 2019.
What is TIR?
Time-in-Range (TIR) is defined as the percentage of time an individual spends with their blood
glucose levels in the target range. The target range varies depending upon the individual, but
general guidelines suggest the range as 70 to 180 mg/dL. The 2019 consensus conference
recommends a target range of 70-180 mg/dL [3.9-10.0 mmol/L] for individuals with type 1 diabetes
and type 2 diabetes, and 63-140 mg/dL [3.5-7.8 mmol/L] during pregnancy, along with a set of
targets for the time per day [% of CGM readings or minutes/hrs]. However, the target range was
lowered for pregnant women to 63-140 mg/dL as the blood glucose levels are lower in pregnancy.
The recommendations also outlined fixing targets for people with diabetes who are older and/or
considered high-risk and the time-in-range bar was set at 50% for this category. Furthermore,
for patients with diabetes the time spent below 70 mg/dL should be less than 1 hour a day and
time spent at or above 180 mg/dL should be less than 6 hours a day. For people with serious
hypoglycemia the time spent below 54 mg/dL should be less than 15 minutes a day and the time
spent above 250 mg/dL should be less than 1 hour and 15 minutes a day.
People with diabetes often experience different energy levels, moods, dietary patterns etc
when they are in TIR, TAR and TBR. There can be many highs and lows in their glucose profile
also. HbA1c, the primary metric for glucose monitoring only denotes the average blood glucose
level for three months period and it does not express how much time a patient spent in
different blood glucose ranges in 24 hours duration. Thus TIR emerged as a better metric beyond
HbA1c in expressing the variations in blood glucose levels that characterize living a life