“In God we trust. All others must bring data”
- WE Deming, American Statistician
I had jokingly cited the above quote while asking the elderly Mrs Reena Khanna (name changed) to bring her Diabetes-related data to me, for an opinion on further management. The data did not look very good, and all her readings were high. Her fasting blood sugar value was 197 mg/dL and her HbA1c value was 10.1 per cent.
Mrs Khanna was already taking three different types of oral pills for Diabetes. The fasting blood sugar level should have been below 110 mg/dL. And the HbA1c test, a single measure that gives an average value of blood glucose control over three months, should have been below 7 per cent.
“Doc, you had advised me last time, but I had not agreed. But now I see that you were correct. I am already following a low carbohydrate diet and doing exercise. I agree, it is time for me to start insulin injection,” she volunteered, after going through the blood sugar numbers by herself.
A number is powerful. It overcomes all subjectivity and allows an objective assessment of the situation. Sometimes, just by focusing on a number, we can conquer emotional and irrational biases that mar our judgment.
For people with Diabetes, a number that reflects their blood sugar level is of utmost importance, for it helps them work with their doctor to improve their care. And to date, among all those numbers, the most important number has been HbA1c or glycosylated haemoglobin. The percentage of haemoglobin that binds to glucose reflects blood glucose control over three months. That is because haemoglobin resides in red blood cells, which have a life of about three months.
For instance, if a person with Diabetes has had a pastry or more on the day prior to testing, the blood sugar level would be high. But if that person had been diligently following diet and exercise over the past three months then the HbA1c would be normal. Such a person does not need escalation of medication. In short, the HbA1c test facilitates decision making. Moreover, high HbA1c is linked to complications of Diabetes such as blindness, foot problems, kidney failure and heart attacks.
However, the HbA1c test has some limitations. Since it is very sensitive to high blood sugar levels, it does not reflect low blood sugar levels or hypoglycaemia. Also, many biological factors including diseases may result in wrong HbA1c estimates. Therefore scientists have been searching for better measurements of blood sugar.
A possible answer has come: the discovery of new glucose sensors. These sensors, which consistently measure blood sugar every few minutes and do so over 14 days, let us know the blood sugar levels even at odd hours of the day. This type of measurement, called continuous glucose monitoring or CGM, requires us to interpret hundreds of blood sugar readings. For instance, if a sensor measures blood sugar every 15 minutes for 14 days; we would have to interpret 1400 blood sugar readings.
One way to interpret these readings is to make graphs, both linear and in the form of bar charts or pie diagrams. This is difficult for people to understand. For the purpose of simplicity, a journal called “Diabetes Care” recently published a consensus statement suggesting a new measure of glucose control, called Time-in-range or TIR.
Simply put, TIR shows the percentage of time that an individual has spent with normal blood sugar levels. If we take the above-mentioned example of 1400 readings over 14 days, how many of the readings were within normal range? Assuming the normal sugar levels should range between 70 mg/dL to 180 mg/dL, the question would be: how many blood glucose levels fall within the range? If 700 out of 1400 values are in range, the time in range would be 50 per cent.
Guidelines state that at least 70 per cent of the blood sugar readings should be within range, and not more than 4 per cent of the blood sugar levels should be below range. For frail and elderly persons like Mrs Khanna, guidelines suggest that only 50 per cent or more readings need to be within range.
This expression of time-in-range (TIR) is easier for people to understand when compared with more complicated tests. Even a 5-10 per cent increase in the time spent in normal range can translate into meaningful improvements in risk of kidney disease or diabetic eye disease. Moreover, as the time-in-range is interpreted along with the time below range, this test would reflect low blood sugar too, unlike the classical HbA1c test.
Some experts suggest that TIR would replace HbA1c. But being an expensive test, it is likely to supplement, rather than replace conventional measures of blood glucose control.
Let me come back to Mrs Khanna and her reply to the quote on everyone except God having to bring data. “Doc, as physicists have discovered the Higgs-Boson God Particle, shouldn’t God also have to now bring data?” she countered. Though I see both faith and science as identical quests for a higher truth, I never discuss matters of faith in a professional setting. In an effort to link science and faith, and to bring the conversation back to Diabetes management, I answered with another quote. This time my quote was from the Mahabharata:
“Of all the measurements, I am Time.”
I proceeded to explain the concept of time-in-range to Mrs Khanna! She seemed to truly enjoy her discussions on Diabetes management. Time-in-range is a smart way to simplify the difficult measures of glucose control.
Dr Unnikrishnan AG