You be the Monitor of your Control

You be the "Monitor" of your "Control"!

Dr. S.M.Sadikot.
Hon. Endocrinologist,
Jaslok Hospital and Research Centre,
Mumbai 400026

You have diabetes and are taking treatment for it. How do you know whether the treatment is helping you bring about your raised blood glucose levels into the range which your doctor has fixed for you?

Obviously, you will have to monitor your control!

Before we discuss the methods by which you can monitor your blood glucose control, one point must be made absolutely clear. What you are aiming for is an "optimal" blood glucose control.

What exactly does this mean?

Optimal control of your blood glucose implies that is around the target levels determined for you throughout the 24 hours, seven days a week!

How will you judge this?

Urine Glucose Testing

Today, there would seem to be no place to use urine sugar testing to judge diabetes control.

At one time, when it was not possible to routinely tests the blood for glucose, testing the urine for sugar was the only means by which one could judge control of diabetes.

The reason for this was that it was felt that when the blood glucose levels became more than 180mg%, then the glucose would overflow and be seen in the urine. This figure of 180mg% was called the "renal threshold" for glucose.

But what you have to realize is that the renal threshold is not a fixed figure relevant to everybody. Your renal threshold may be entirely different. In fact we know today that there are many people who do not show any sugar in the urine inspite of their blood glucose being over 300mg%. Conversely, there are people who will show the presence of sugar in the urine even when the blood glucose values are 100mg%!

Another way to look at this, is to accept that the renal threshold is 180mg%. Let us also accept that the urine when tested shows the absence of sugar. What can this mean? Does this show that one is in good control?

Definitely Not!

The blood glucose could be anywhere between 0mg% to 180mg%, in other words the absence of sugar in the urine could show a blood glucose level ranging from such low levels that one cannot be alive, to very low levels, to normal levels, right up to unacceptably high values.

And if this was not enough, the renal threshold of every person changes with the level of diabetes control. In other words, the very parameter which you are using to judge control changes as your control changes! One could say that this would be in cricket, if the rules for, say, LBW changed with every ball bowled. Obviously, no one could play cricket under these circumstances.

Then how can we use such a parameter to judge control?

But urine testing still continues to be used, possibly because it is cheap. So, if one is going to use this parameter, then it is important that one be aware of the limitations:
  • In many cases, marked hyperglycemia may occur without glucosuria and conversely, significant glucosuria may be seen with euglycemia.
  • The urine glucose levels do not correspond to the prevailing blood glucose levels at the moment of testing.
  • A negative test does NOT distinguish between hypoglycemia, euglycemia and mild to moderate hyperglycemia.
  • Urine glucose tests do not give warning of impending hypoglycemia.

Urine glucose testing given its limitations, should NEVER be used alone to assess glycemic control or make changes in the management. If used, it should always be supplemented by periodic blood glucose tests.

  • If urine glucose remains consistently very high, one should always check the blood glucose levels immediately.
  • Conversely, in the presence of a very high blood glucose values, the urine should be checked for the presence of acetone.
Laboratory Blood Glucose Tests

For most of you, periodic blood glucose testing in the laboratory is the usual method used to evaluate your glycemic control.

It is recommended that such blood glucose tests should be carried out every month, or more frequently if necessary. The blood glucose should be estimated in the fasting and/or post-prandial state; a random blood glucose estimation, often, can give valuable information about the immediate status of the patient's glycemic control.

One thing which is very important to remember is that your usual diet and medications should be continued on the day of the test.

It is important that you must know the shortcomings of this method of judging control. You should realize that such occasional blood glucose tests only reflect the PREVAILING blood glucose levels at the PRECISE TIME at which the blood was collected. It CANNOT give a true picture of the blood glucose levels during the intervening period between two tests.

Thus, such occasional blood glucose estimations do NOT allow accurate assessment of the overall GLYCEMIC CONTROL.

SMBG is one of the most useful methods to assess glycemic control.

Ideally, all patients should self monitor their blood glucose levels, using test trips and meters which are now available.

If it is not feasible, SMBG should be carried out by:

  1. All patients on insulin therapy, especially those on multiple dose regimens.
  2. Patients with widely fluctuating blood glucose levels.
  3. Patients prone to severe ketosis or recurrent hypoglycemia.
  4. Those manifesting hypoglycemia "unawareness".
  5. Patients in whom a "tight" control is essential, i.e. pregnancy, etc.; during acute illness.
  6. In the perioperative period.
  7. Those with abnormal renal thresholds.
Self Monitoring of the Blood Glucose

Glycosylated Hemoglobin (HBA1c) Estimation

Sugar levels fluctuate from minute to minute, hour to hour, and day to day. Thus for hour to hour control, or day to day, we need a parameter which will give us an overall idea of the blood glucose control.

The hemoglobin A1c (HbA1c) test is a simple blood test that indicates how well your diabetes has been controlled over the past three months. Unlike daily blood glucose testing, which measures your blood glucose level at the moment you test, the HbA1c test provides a broader picture of your overall glucose control.

In the blood stream, glucose molecules get attached to protein molecules which are present in the blood. Hemoglobin is a protein in red blood cells that carries oxygen. Hemoglobin picks up glucose from the bloodstream, becoming "glycated." As blood glucose rises, so does the level of glycated hemoglobin.

Thus, the presence of glycosylated hemoglobin is a normal occurrence and HBA1c is present even in those who do not have diabetes.

Glycosylated hemoglobin
Normal
Glycosylated hemoglobin
High

If more glucose molecules are present in the blood, as would occur in a person with raised levels of blood glucose, then the number of glucose molecules which would get attached to the proteins, such as hemoglobin would increase and this would be seen as raised levels of HBA1c.

glycosylated haemoglobin
Haemoglobin in the blood (red, rectangle) combines with glucose in the blood (green, circle) to form glycosylated haemoglobin. This reaction occurs over a 10 week period.
glycosylated haemoglobin
Controlled diabetes, not much glucose, not much glycosylated haemoglobin
glycosylated haemoglobin
Uncontrolled diabetes, more glucose, much more glycosylated haemoglobin

Once hemoglobin becomes glycated, it remains that way for the life of the red blood cell, which is three to four months. This means the HbA1c test can provide a picture of your glucose control over several months.

Test results reflect the percentage of glycated hemoglobin in your bloodstream. People without diabetes typically have an HbA1c level of 5%. Studies have shown that people with diabetes who are able to keep their levels at 7% or less reduce their risk for complications such as blindness, kidney disease and nerve damage.

It is also possible to get an idea of your average blood glucose levels by estimating the HBA1c levels.

Blood Sugar

You should have the test every three to four months. It is a simple test that requires only one sample of blood. There is no need to fast. The sample can be taken at any time of the day -- even right after a meal.

  • This estimation gives an average of the blood glucose levels over the previous two weeks.
  • Especially useful in monitoring glycemic control in certain situations like pregnancy, etc., where intervals of 6-8 weeks as in GHb estimations may not be optimal.

Presently, self monitoring of the blood glucose levels, along with 12 weekly HBA1c estimations would seem to be the ideal method to monitor blood glucose control in patients.

But this may not be feasible, or economically viable, for many patients.

Most importantly, you must realize that monitoring your blood glucose levels is not the same as mentoring your diabetes!

Besides glycemic control, optimal monitoring in diabetes, implies optimising the weight, blood pressure, lipid abnormalities, and importantly, the diagnosis of the presence of long term complications in their early, initial stages.