Blood Glucose Monitoring

The ability of the diabetic patient to monitor the effect of their treatment on their blood glucose levels remains one of the major challenges of diabetes care.

At long last exciting new methodology appears to be on the horizon. At present, however, most patients self-monitor their blood glucose using a wide array of commercially available blood glucose meters which all achieve clinically acceptable standards of accuracy and precision at least in laboratory assessment. Not all patients (nor indeed nurses and doctors in hospital wards) are able to achieve such standards. This emphasizes the need for adequate instruction in the technique and regular quality-control assessment. Unfortunately, finger pricking to produce an aliquot of blood for self-monitoring is an unpleasant procedure, certainly associated with more discomfort than insulin injections. This may inhibit the performance of testing using current technology.

Blood glucose measurements are taken before and after meals and, on the basis of a profile of several days' readings, a decision is made regarding the need to alter the insulin dosages. In practice, however, although most patients become reasonably adept at blood glucose measurement, only a minority of patients acquire the skill of appropriate adjustment of insulin dosages. The exception to this seems to be most patients who have been on a DAFNE course as alluded to below.

Furthermore, there is controversy as to the minimum number of readings required each day. A compromise would be two readings per day with variations in the timing of the readings on alternate days. Alternatively profiles of four or more readings may be done on selected days during the week. More intensive monitoring is recommended during intercurrent illness and when insulin treatment is being changed or adjusted.

Among the more tangible benefits of self-monitoring are that the technique allows patients to recognize that certain symptoms represent hypoglycemia and that the ingestion of certain foods leads to an unacceptable increase in blood glucose concentration. It also allows the assessment of the individual's glucose response to various types of exercise. There is no conclusive evidence of benefit of self-monitoring of blood glucose in patients with type 2 diabetes except for those on insulin therapy, although, it may be helpful during concurrent illness.

Clearly recognized disadvantages of current blood glucose sampling systems are the need for skin lancing and the practical limitations of obtaining samples frequently enough to allow meaningful manipulation of insulin dosage with either subcutaneous injections or continuous pump methods. Technological progress has been made here in the development and availability of continuous glucose monitoring using a subcutaneously implanted continuous monitoring system (MiniMed Inc., Sylmar, CA, USA). The subcutaneous sensor is connected by a cable to a monitor/microprocessor device that is worn externally (Figure 69). Interstitial fluid glucose is measured frequently and the data are downloaded at a later time. This information can then be used to refine and adjust patients' diabetes management resulting in improved glycemic control and avoidance of hypoglycemia. Studies to date have demonstrated disturbing changes in blood glucose values that could not have been anticipated using conventional self-monitoring techniques. A wristwatch-like device that uses a process known as reverse iontophoresis and is able to produce similar results on a real-time basis with warning of hypoglycemia has been marketed, but has not proved to be as useful and as acceptable in practice as had been thought at product launch.

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