Postprandial or Not Postprandial, That is the Question.

If your patient is only willing to check once a day, which do you want them to know, their best or their worst? 

 It’s easy for us to ask our patients to check multiple times a day but we all have patients who won’t do it more than once a day. 

I have told many my patients “ knowing your best sugar will not keep you from going blind, knowing your worst will. 

The purpose of glucose testing is to allow patients with diabetes to achieve optimal glycemic control while avoiding hypoglycemia. As many patients with diabetes tend to have relatively high fasting glucose levels in the morning, a phenomenon referred to as the "dawn phenomenon,"^[1] restricting glucose measurements to this time decreases the likelihood of detecting low glucose levels, which typically occur in the late afternoon and, more dangerously, during the night. Furthermore, hypoglycemia may occur at different times in different patients. Thus, a strategy of testing glucose at various times during the day is more likely to detect low glucose levels and hence decrease the likelihood of hypoglycemia.

Many glucose-lowering agents, such as metformin, the thiazolidinediones, perhaps the sulfonylureas, and the intermediate- and long-acting insulins given at night, show their greatest effect in the fasting period. Monitoring only fasting glucose levels might lead to the mistaken belief that glycemia is under control, while in actuality there is suboptimal glucose control during the day requiring additional efforts at treatment. Both nocturnal hypoglycemia and fasting hyperglycemia are commonly found in patients with type 1 diabetes,^[2] and have been frequently documented with new continuous interstitial glucose-monitoring devices.^[3]

The dissociation between fasting and daytime glycemia appears to explain the failure of conventionally treated type 2 patients in the United Kingdom Prospective Diabetes Study (UKPDS) to achieve stable control of HbA1c during the 10-year study, in contrast to the relatively stable fasting glucose achieved in the insulin intervention group.

There is another question to be addressed, however, which is whether postprandial glucose measurement should be performed in addition to preprandial measurement, so that one might consider asking the patient with diabetes to test the blood glucose before and 90-120 minutes after each meal, at bedtime, and during the night, for a total of 8 potential testing times. There is a great deal of evidence that the post challenge glucose is more sensitive than fasting glucose in the diagnosis of diabetes and in the prediction of macrovascular risk in large populations.^[4]

There is also evidence that postprandial glucose shows a stronger correlation with HbA1c than does fasting glucose.^[5] During pregnancy, regular postprandial monitoring is certainly accepted, supported by evidence that patients using postprandial glucose goals have improved fetal outcomes.^[6] We do not yet have evidence that using postprandial glucose as a therapeutic target particularly benefits other patients with diabetes.

However, various therapeutic agents specifically target postprandial glucose. These are the alpha-glucosidase inhibitors acarbose and miglitol, the rapidly acting insulin secretagogues repaglinide and nateglinide, and the short-acting insulin analogues lispro and aspart, as well as the inhaled and oral insulin preparations now being developed. Future studies with these agents using continuous glucose monitoring technologies will greatly increase our ability to understand the relative benefits of pre- and postprandial glucose as therapeutic targets and will allow a more complete answer to the question of whether patients should routinely monitor postprandial blood glucose. At present, it seems that monitoring postprandial glucose is logical for patients undergoing treatment with these agents or for whom such treatment is being considered.

Patients can also learn if they have had to much too eat and even learn which foods cause the blood sugars to increase more dramatically by checking their postprandial readings. 

For patients with type 2 diabetes it is not usually appropriate to recommend extremely frequent glucose testing, and our practice is to suggest that each day a different meal be "bracketed" with pre- and postprandial glucose tests, so that over the course of a week two 6-point day-profiles can be generated. Such an approach can be used to adjust doses of each meal's medication, with many patients requiring smaller doses before lunch and larger doses before dinner, particularly with repaglinide and rapidly absorbed insulin preparations.

References

1. Bolli GB, Gerich JE. The "dawn phenomenon"--a common occurrence in both non-insulin-dependent and insulin-dependent diabetes mellitus. N Engl J Med. 1984;310:746-750.

2. Holl RW, Grabert M, Schwab O, et al. Factors related to the prevalence of nocturnal hypoglycemia in hospitalized children and adolescents with type 1 diabetes mellitus: Analysis in 2659 subjects from 62 centres. Diabetes. 2001;50(suppl 2):A67.

3. Gibson LC, Halvorson MJ, Carpenter S, Kaufman FR. Short-term use of the MiniMed Continuous Monitoring System to determine patterns of glycemia in pediatric patients with type 1 DM. Diabetes. 2000;49(suppl 1):A108.

4. The DECODE Study Group. Glucose tolerance and mortality: comparison of WHO and American Diabetes Association diagnostic criteria. The DECODE study group. European Diabetes Epidemiology Group. Diabetes Epidemiology: Collaborative analysis Of Diagnostic criteria in Europe. Lancet. 1999;354:617-621.

5. Avignon A, Radauceanu A, Monnier L. Nonfasting plasma glucose is a better marker of diabetic control than fasting plasma glucose in type 2 diabetes. Diabetes Care. 1997;20:1822-1826.

6. de Veciana M, Major CA, Morgan MA, et al. Postprandial versus preprandial blood glucose monitoring in women with gestational diabetes mellitus requiring insulin therapy. N Engl J Med. 1995;333:1237-1241.
   
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