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MONITORING GLYCEMIC CONTROL

Optimal glycemic control implies that the blood glucose levels throughout the 24 hours, on each day, are at the target levels determined for each individual patient.

METHODS USED IN MONITORING GLYCEMIC CONTROL

Urine Glucose Testing

  • The basis for using glucose tests is the renal threshold for glucose which is roughly correlated with hyperglycemia; thus, urine tests for the presence of glucose, may have a role to play in monitoring glycemic control, if the renal threshold of the patient is normal and stable.

  • Unfortunately, some patients with raised blood glucose levels may show no urine glucose, whilst others with a normal blood glucose may show evidence of glucose in the urine.

  • Inspite of these limitations, urine glucose testing continues to be widely used to assess diabetes control.

  • In patients with a "normal" renal threshold, and being treated with diet alone, or diet and small doses of OHAs, it is desirable to get all the urine samples (pre-and post-prandial) glucose free.

  • In patients on insulin, one should try to get all the pre-prandial urine samples free of the presence of glucose.

If urine glucose tests are used to monitor glycemic control, one must 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.

Blood Glucose Testing

Laboratory Blood Glucose Tests

  • Along with urine glucose testing, periodic blood glucose testing in the laboratory is the usual method used to evaluate 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.

The usual diet and medications should be continued on the day of the test.

  • The method used for the determination must be the glucose oxidase method; many laboratories continue to use the older, and outdated, Folin-Wu or Somogyi-Nelson methods which should be actively discouraged.

  • 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 ambient 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.

Self Monitoring of the Blood Glucose (SMBG)

  • 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.

SMBG measures capillary glucose which gives values around 15% higher than the venous plasma glucose, especially in the postprandial state. The values may be closer in the fasting state.

The routine use of SMBG in NIDDM'S who do not fit into the above categories is controversial, but is generally felt to be advisable, especially if this is feasible.

JUDGING LONG TERM GLUCOSE CONTROL
Glycosylated Hemoglobin (GHb) Estimation

  • An excellent test to judge overall glycemic control.

  • This gives an idea of the average blood glucose levels over a longer period to time. An optimal level implies adequate control over the previous 6 to 8 weeks.

  • Falsely elevated results may be obtained in patients with renal failure and, conversely.

  • False low levels in patients who have associated problems with a shortened red blood cell life span.

  • Normal values will depend on the individual laboratory and the methodology used.

Serum Fructosamine Levels

  • 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.

OPTIMUM MONITORING

Presently, self monitoring of the blood glucose levels, along with 12 weekly ghb 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.

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.


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