Time in Range V/S Hba1C

Dr Rajesh Javherani explains how continuous glucose monitoring presents a comprehensive view of blood sugar levels.
Time in Range V/S Hba1C

Need for testing in Diabetes

As a child I remember my grandfather checking his blood sugar levels by doing a urine test. It was a benedict solution, to which he would add a few drops of urine and would heat it. The change in the colour would give him an approximate idea of his blood sugar levels. However, this process was arduous and  erroneous.

From the urine dip sticks to capillary blood glucose sticks, blood sugar testing methods have evolved and metamorphosed. The silent nature of Diabetes makes testing very important. Testing helps the target values to be attained. Self-monitoring of blood glucose at home has become important in the life of a person with Diabetes. However, each reading only gives a stat value of blood sugar levels. The more frequent the sugars are checked, the better will be the understanding  of sugar control.

Rise of HbAlc

Sometime in 1980's a test called HbAlc (glycosylated haemoglobin) was introduced which gave an estimate of average glucose value over a three-month period. The ideal target HbAlc value is 6.5 per cent, however it could vary according to the age of the patient.

Shortcoming

Imagine two people with similar HbA1c ranging between 6.5 to 7 per cent. However person A has his glucometer sugar values dose to 140-170 mg/dl and person B has

ugar values ranging from 60 to 280 mg/dl with history of hypoglycaemias or low blood sugar level. Both people have similar

HbAlc, however person B doesn't have a good control of his blood sugar levels.

Continuous glucose monitoring

Continuous glucose monitors (CGM) have transformed and recast the treatment of Diabetes.The monitors are easy to use and observe blood sugar levels. They also help the doctor better understand the blood sugar profile. Continuous glucose monitoring system consists of a small sensor that is attached over the skin. It measures the glucose values in the interstitial space between the cells and transmits wirelessly to a small device or even to a smart phone.

This technology measures glucose levels every 5 to 15 minutes, depending on the CGM used. The blood sugar values are then plotted over a graph, and this graphic representation highlights the daily fluctuations.

Time-in-range

lime-in-range (TIR) in simple words means the amount of time the glucose values fall in the range (70-180 mg/dl) during a 24- hour period in patients who use CGM. The American Diabetes Association guidelines mention that at least 70 per cent of time the blood sugar values should fall in the above-mentioned range. The target range could sometimes varyThe graph above highlights the glucose profile of a patient with Type 2 Diabetes.

The grey band is the targets set for the glucose level, which is set at 70-180 mg/dL. One can see the column on the right which shows the TIR. In this particular glucose profile, of the 8 days only twice the blood sugar values have fallen in the range more than 70 per cent of the set target range.

The rest of the days there are fluctuations between hypoglycaemia and hyperglycaemia (high blood sugar levels). Without this data, generated by CGM, it would have been impossible to know this detailed blood sugar profile. lime above target and time below target also denotes hyperglycaemia and hypoglycaemia respectively.

TIR and Diabetes management

HbAlc and snapshots of self-monitoring of blood sugar values do not provide a detailed insight to the unfolded blood sugar values provided by the CGM. The CGM generated blood sugar profiles are utilised in making changes to keep the sugar values in range. Any hyperglycaemias and hypoglycaemias seen in the blood sugar profile can be simply dealt by changing dietary patterns and modifying physical activities. This prevents unnecessary changes in doses of medications. People with Type 1 and 2 Diabetes on insulin therapy find it easier to adjust their insulin doses after analysing the CGM generated data. By keeping blood sugar levels within the TIR, Diabetes related complications could be minimised. It is evident that marked blood sugar fluctuations are related to a greater number of complications. There is also a lesser incidence of hypoglycaemia when one keeps glucose values in TIR.

To conclude

HbAle alone does not provide adequate information for day-to-day Diabetes management. It does not recognise the fluctuations in blood sugar values. It tells you only the average sugar values over the last 3 months. Diabetes management should be tailored to improve the quality of life of people with Diabetes.

However TIR as a metric is now more used to identify daily blood sugar profiles over a period of 14 days. It provides a more realistic picture of day-to-day blood sugar levels and also empowers people to take charge of their Diabetes especially in-between follow-up visits as the information is easily accessible. In simple words, CGM and TIR data opens an in-depth world of blood sugar values for better management of Diabetes and avoidance of its varied complications.

Dr Rajesh Javherani is a Chief lntensivist and

Consultant Physician at Victor Hospital, Goa.

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