TIME TO UNDERSTAND ‘TIME IN RANGE’

It is estimated that about a half a billion people are living with diabetes worldwide. Most of them will have Type 2 diabetes, with about 10% living with Type 1 diabetes. Large scale studies have proven that good glucose control reduces the complications associated with diabetes: cardiovascular disease, such as heart attack and stroke, kidney disease, vision loss and amputations.

At the heart of this statement are the words ‘good glucose control’.

Until now, two main parameters have been used to determine diabetes control:
⦁ Home glucose levels using glucometers
⦁ HbA1c – the 3 month test showing average glucose levels

TIME TO UNDERSTAND MEASURING GLUCOSE READINGS
Testing blood glucose regularly is an onerous task. It is important therefore, to test with purpose. Guidelines suggest that PWD treated with oral medications can measure blood glucose levels 2-3 times weekly. The timing of the test can vary from a fasting blood glucose to 2 hours post meal. PWD using insulin will have to check their glucose readings more frequently. As a rule, the minimum tests should equal the number of injections per day. For PWD on 4-5 injections daily, this is taxing. However, we know that more frequent glucose testing does improve diabetes control.

HOW TO UNDERSTAND CONTINUOUS GLUCOSE MONITORING
CGM devices are the machines of many a PWD’s dreams: a way of always seeing the blood glucose without having to open a conventional glucometer and prick a finger. As the CGM devices became more advanced, they not only showed the current glucose reading, and of course the tracing of where the glucose had been but could predict where the glucose would go. In this way PWD can be forewarned of a hypoglycaemia or hyperglycaemia and take appropriate action to avoid these. When this type of CGM technology works in tandem with insulin pumps, we see the makings of an artificial pancreas.

TIME IN RANGE
What data from CGM shows is that we cannot always rely on average blood glucose levels, even HbA1c, to fully assess overall diabetic control. Averages do not show the extend of the high and low glucose readings. Let me explain. If there are three blood glucose values of 6.0mmol/L, then obviously the average blood glucose is 6.0mmol/L. However, three readings of 12mmol/L, 2mmol/L and 5mmol/L will also give an average of 6.0mmol/L and yet only one reading is in the target range. This variation in glucose levels is called GLUCOSE VARIABLITLY. CGM demonstrates patterns of glucose over a 24- hour period in detail so the swings in blood glucose levels are easily seen. The more frequently the blood glucose levels swing from highs to lows, the higher the glucose variability. There is concern that this variability can damage blood vessels and thus, may be implicated in diabetic complications.

GLUCOSE TARGETS
Based on data from all the large diabetes trials over the years, we can set targets for good diabetes control. This is not a one-size fits all range. Age, duration of diabetes, presence of complications, risk of hypoglycaemia and pregnancy all affect the target blood glucose levels. In older PWD who have diabetic complications, particularly of the heart and kidneys, glucose levels are slightly higher than a young, newly diagnosed PWD. Table 1 shows advised targets for FBG, PPG, HbA1c.
In 2019 the International Consensus in Time in Range (TIR) defined the desired targets for CGM readings. If blood glucose levels remain between the values of 4.0mmol/L and 10mmol/L 70% of the time (Time in Range – TIR), the corresponding HbA1c is around 6.5%. That equates to excellent diabetes control. Time below range (TBR) refers to readings < 4mmol/L and Time above range (TAR) gives the percentage of time glucose readings are above 10mmol/L. Fig. 4 illustrates the ideal range for patients with Type 1 and Type 2 diabetes and in pregnancy. Several medical aids will now consider reimbursement (with various levels of co-payment) for people living Type 1 diabetes who wish to use CGM devices.

SUMMARY
Good control is not only a good average glucose, but also stability of glucose levels over time. Time in Range gives us insight into glucose stability and may become the most important of all glucose measurements in the future.

International Consensus of Time in Range.

Battelino T et al., Diabetes Care 2019; https://doi.org/10.2337/dci19-0028