Download Clinical Care Part I

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.

Presently, the following methods are in use:

1. Testing the urine for the presence of glucose;
2. Occassional blood glucose test done in an laboratory;
3. Estimation of Glycosylated Hemoglobin and serum Fructosamine levels;
4. Self monitoring of the blood glucose levels;

Urine tests are associated with too many shortcomings to give any reasonable answer about the glucose control. Testing the urine for the presence of glucose as an indirect parameter to judge blood glucose control is, at best, a crude method and should be accepted as such.

Many commonly used drugs interfere with the results.

For a partial list of such drugs see Appendix 7a

The problem is further complicated by the fact that there are some drugs which by themselves cause glucosuria and would tend to give a false positive result for the presence of glucose in the urine.

For a partial list of such drugs see Appendix 7b

The parameter which is most commonly used to judge glucose control is the occasional, even if regular, glucose check in laboratories. Patients are usually seen at 2-3 monthly intervals and the fasting and the 2 hour post lunch glucose levels are estimated.

Such occasional blood glucose estimations cannot give adequate information to allow us to rationally make these suppositions.

Methods for Estimating Blood glucose levels

The blood glucose levels must be estimated using the latest accepted methods such as the glucose oxidase/hexokinase based techniques.

Both Folin-Wu and Somogyi-Nelson as well as the later Ferricyanide techniques Ortho-toluidine methods the are now obsolete and should not be used.

Many laboratories continue to estimate the blood "glucose" by these methods.

They are not very specific and estimate not only glucose but also many other substances, including medications and drugs, present in the blood and which will not allow a correct evaluation of the glucose levels.

For a partial list of such drugs see Appendix 7c

Moreover, there can be a significant difference in the results depending on whether the glucose has been estimated on whole blood or plasma or glucose and even from where the blood has been collected. It is not widely appreciated that if the blood is collected from the back of one's hand, the glucose values will be about 10-15mg% more than if the blood has been collected from the front of one's elbow?

The time that elapses between the collection of the blood sample and its estimation also affects the results. Blood glucose levels will decrease at a rate of about 7-10 mg/dl per hour at room temperature unless the red cells are removed or their enzyme systems inhibited. Fluoride ion is commonly used for this purpose. The greater the interval between the time of collection of the sample and the estimation, the lower will be the glucose result. This is in spite of whatever preservative that many laboratories add. It is obvious that there is no standard time interval at which laboratories do the glucose estimation.

Rough handling, contamination, or inadequate refrigeration of the blood sample can cause inaccurate test results.

Such, occasional blood glucose estimates cannot be used to correctly adjust the treatment and these estimates should really be called guesstimates (as the Americans with their penchant for joining two words call it), and accepted as such. Any change in the treatment made on the basis of these random blood glucose reports can, at best be based on guess work, and not on solid clinical grounds.

HbA1c

An estimation of the Glycosylated Hemoglobin (HbA1c) levels allows the glycemic control to be judged over a span of time.

The estimation of HbA1c levels is also more convenient for the patient. The blood for the estimation can be collected at any time and the patient does not have to be in a fasting stage or at any fixed interval after a meal. Thus, the blood collection can be done even when the patient comes for his routine checkup at any convenient time.

Approximating Serum Glucose

Hemoglobin A1C of 6% represents mean glucose of 130 mg/dl

Each 1% increase in A1C, glucose increases approximately 30 mg/dl

Hemoglobin A1C interpretation

NOTE: All glucose values are in mg/dl

Hemoglobin A1C: 5.5% represents mean glucose of 100
Hemoglobin A1C: 7.0% represents mean glucose of 150
Hemoglobin A1C: 8.0% represents mean glucose of 180
Hemoglobin A1C: 9.0% represents mean glucose of 220
Hemoglobin A1C: 10.0% represents mean glucose of 250
Hemoglobin A1C: 11.5% represents mean glucose of 300
Hemoglobin A1C: 13.0% represents mean glucose of 350

NOTE: These figures are merely approximations and can vary depending on sampling methods, laboratory assay techniques and laboratory error. The assay method need to be known in order to approximate the blood glucose levels from the HbA1c readings.

One MUST make sure that what is estimated is the HBA1c, by an accepted and standardized method. Besides the method used to estimate the HbA1c levels, there are some factors which must be kept in mind when analyzing the results of the HbA1c tests.

For a list of factors which may result in false results see Appendix 7d

The introduction of glucose meters has to a large extent completely revolutionized the monitoring of blood glucose levels. Not only can the patient use these meters to self monitor the blood glucose values (SMBG), but as importantly, the wide availability of these meters allows doctors to closely monitor the glycemic control of their patients and adjust therapy to attain optimal control.

Which patients should monitor their blood glucose levels?

Ideally, all patients should be carrying out SMBG but if this is not feasible, it should at least be done by:

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

How often should a patient self monitor the plasma glucose levels? Patients on multiple insulin injection regimens, patients with critical problems such as those with sight threatening macular edema and infections, and pregnant patients in whom a tight control is mandatory should preferably monitor their blood glucose two to three times daily. They should be taught how to adjust their doses depending on the levels. If in spite of this, the blood glucose remain high, they should seek medical attention immediately.consult their doctor at once.

Patients who may not fall in these "critical" categories, are asked to test the blood glucose daily at different times for about 1-2 weeks or until they are confident about the method of testing and are optimally controlled. Once this is done, they are asked to test the blood twice or thrice a week just to make sure that the control remains at an optimal level. In case, they find that the control has deteriorated, then they should revert back to a more intensive frequency of testing and take the corrective measures until the control is back to the original optimal levels. Once the control has been optimised, the frequency of testing can be reverted back to twice or three times a week.

Always advise all people using the meters that they should have periodic comparisons between the meter readings, especially in the fasting state and a sample obtained simultaneously and measured by a good laboratory.