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Managing Diabetes

More about Blood Glucose Monitoring: when to test - before or after meals?

A discussion about Pre-prandial and Post-prandial measurements.

Introduction

The greatest influence on your daytime blood glucose levels is from your meals. It therefore makes sense to time your glucose tests around meal time. In people who do not have diabetes, glucose levels in the blood reach a peak about an hour after meals, whereas in people with type 2 diabetes peak levels occur about two hours after meals.

What does pre-prandial and post-prandial mean?

Most people have three meals a day. Based on this, there are seven useful time points during the average day when it is worthwhile measuring your blood glucose levels.

These time points are before meals (pre-prandial measurements), after meals (post-prandial measurements), and at bed-time. Post-prandial means ‘after meals’.

The pre-prandial measurement before breakfast is also called fasting blood glucose.

If you have diabetes, there is little value in testing your blood glucose levels less than two hours after meals as your glucose concentrations are likely to be high. As a general rule therefore post-prandial measurements are obtained two hours after you have eaten.

What influences fasting and pre-prandial blood glucose?

This largely depends on the rate at which glucose is produced by the liver. How much insulin is released by the pancreas and how sensitive your body is to insulin also play a major role.

What influences post-prandial blood glucose levels?

Your post-prandial blood glucose will vary with the content of your meal. For example a meal high in carbohydrates will give you a higher peak than a meal which is high in fat. Physical activity and how sensitive your body is to insulin also makes a difference.

There are many complex interactions which influence post-prandial blood glucose which are of great interest to diabetologists. This interest has recently been heightened due to a range of new medications which specifically target post-prandial blood glucose. These include the rapid acting insulin analogues, insulin lyspro (Humalog) and insulin aspart (NovoRapid), GLP-1 agonists and amylin analogues.

Which measurement is better – should I measure blood glucose before or after meals?

Home blood glucose testing is time consuming, costly and by no means painless. You should therefore discuss the most suitable regimen with your doctor or diabetes specialist nurse, indeed you may not need to monitor your glucose concentrations at all!

It is interesting to note that despite much research into the subject, there is no consensus with regard to which measurement is ‘better’. There is also no evidence that targetting either measurement results in more effective lowering of HbA1c.

Monitoring your blood glucose levels before meals is easier to time and subject to less variability. It is also less demanding in terms of time.

Who would benefit from monitoring post-prandial glucose levels?

Monitoring post-prandial glucose has not been shown to influence outcome except in gestational diabetes (diabetes in pregnancy). However if your HbA1c is unnaceptably high despite ‘well controlled’ blood glucose levels there may be an argument for testing your post-prandial glucose concentrations.

 

Dr Nishan Wijenaike MD FRCP
Consultant Diabetologist
West Suffolk Hospital NHS Trust
Bury St Edmunds
August 2007