CHEARS

Haemoglobin A1c test (HbA1c) has been used as a gold standard of glycaemic control since DCCT, while the self- monitoring blood glucose (SMBG) has been a cornerstone of diabetes care to verify glucose variability (GV) on daily basis . HbA1c reflects blood glucose concentrations over three to four months and is the only parameter of glycaemic control that has strongly been associated with chronic diabetic vascular complications. HbA1c does not distinguish individuals with similar average glycaemia but with pronounced differences in hypoglycaemic events and/or hyperglycaemic excursions.

Whereas SMBG provides a “snapshot” of the glucose values and it is used both to titrate prandial insulin doses and to define correction bolus, but does not detect fluctuations that might occur between each capillary glucose test unless testing is done consecutively over short periods.

In 2017, an International Consensus on the Use of the Continuous Glucose Monitoring standardized the use of CGM and recommended the analysis together with HbA1c to promote therapy adjustments in both type 1 (T1DM) and type 2 (T2DM) diabetes mellitus, especially for patients with frequent hypoglycaemia.

With the rapidly developing technology and increasing use of continuous glucose monitoring (CGM), CGM had been the optimal method to get information on glycaemic profile throughout the day.

The main benefit of CGM is observed in high-risk patients with frequent or severe hypoglycaemia, and those with impaired awareness of hypoglycaemia. CGM can be effectively used in patients either in multiple daily injections (MDI) treatment or in those with continuous subcutaneous insulin infusion (CSII)

Although CGM can retrospectively provide 24-hour blood glucose monitoring data, high cost of equipment and the accuracy requirement of frequent fingertip blood glucose have become significant barriers to the widespread clinical use of CGM.

In recent years, the concept beyond glycosylated haemoglobin has been proposed, and the target time in range (TIR) blood glucose value (generally defined as 3.9∼10.0 mmol/L) generated by CGM has become hotspot in research for the clinical efficacy and risk assessment of diabetic complications.

TIR correlates highly with HbA1c, suggesting that TIR may be used as a novel and promising metric in assessing the risk of diabetes complications and glycaemic status in diabetic patients.

Compared with HbA1c testing, TIR provides more sensitive and accurate results. As an example, TIR assessment can record acute events of hypoglycaemia or hyperglycaemia at any time. Obviously, this data cannot be obtained in HbA1c assessment.

TIR is a very promising core indicator for clinical glycaemic assessment, and the risk of diabetic complications, including complications such as urinary microalbumin-tourinary creatinine ratio (ACR), diabetic peripheral neuropathy, cardiovascular disease, and other diabetic complications has not been publicly reported.

How it works:

TIR basically moves away from a single precise measurement of blood sugar (or blood glucose, as it’s known medically), to give people a sense of how often they are staying within the desired healthy range (roughly 70-180 mg/dL).

It uses continuous glucose monitor (CGM) data to “count” the actual amount of time each day a person with diabetes (PWD) stays within those desired control limits, expressed in average hours and minutes over any period of days, weeks, or months.

That’s very different from the traditional “gold standard” measurement of blood glucose control that most PWDs are familiar with, the A1C test. That test, in fact, only provides an average of blood sugar levels over the previous 3 months which is poor at reflecting change and does not measure variability. That means a “good” A1C result of 6 to 7 percent could be nothing more than a midpoint between severe daily high and low blood sugars over several months.

This is a problem; as increasing research shows that variability may play nearly as large a part in poor diabetes outcomes as do the sugar levels themselves.

TIR, on the other hand, reflects the number of actual hours that a PWD remains in healthy blood glucose range over a given period.

In summary, TIR could be considered as a promising indicator of short-term glycaemic control and a predictor for the risks of long-term diabetic complications.

So the question is will TIR actually replace A1C in the future?