Evidence indicates that high levels of glucose concentration following a meal and not fasting glucose are critical to diabetes risk assessment
The most critical parameters are those that enable identification of asymptomatic individuals who have the greatest attributable risk of morbidity and mortality. Fasting glucose concentrations [7.0 mmol/L, based on the American Diabetes Association (ADA) criteria] alone or impaired fasting glucose (IFG, a fasting plasma glucose of 6.1–6.9 mmol/L) cannot fully identify individuals at increased risk of death due to hyperglycemia.
Impaired Glucose Tolerance
In a comparison of the WHO criteria (which base diagnosis of diabetes on both fasting and 2 h glucose concentrations) and ADA recommendations, the DECODE (Diabetes Epidemiology Collaborative analysis Of Diagnostic Criteria in Europe) study finds that oral glucose tolerance tests (OGTT) provided additional prognostic information that cannot be obtained from fasting glucose screening alone.
Researchers from the European Diabetes Epidemiology Group analyzed data of over 25,000 patients from 13 prospective European cohort studies. In the mean follow-up time of 7.3 years, there were 2000 deaths from all causes. In the DECODE Study, people with impaired glucose tolerance (IGT) and a normal fasting glucose (6.0 mmol/L or lower) formed the group with the largest number of excess deaths. This group constituted a third of all men and half of all women with any degree of glucose intolerance. Therefore, screening for IGT can reveal valuable prognostic information related to the risk of death that cannot be identified from fasting glucose levels alone
Postprandial Glucose vs Fasting Glucose
Analysis of the large DECODE database, with more than 180,000 person-years of accumulated follow-up in populations from various parts of Europe showed that high 2 h postprandial blood glucose concentrations are associated with an increased risk of death. Adjusting for the 2 h glucose, fasting glucose was not independently related to all-cause mortality. Fasting blood glucose was not associated with increased death in individuals with impaired glucose tolerance. The risk of death for impaired fasting glucose was lower than that for impaired glucose tolerance. However, an increase in postprandial glucose resulted in a linear increase in mortality among diabetics with impaired fasting glucose. The DECODE investigators, therefore, concluded that fasting glucose levels were unreliable in identifying individuals at increased risk of death associated with hyperglycemia. In fact, among people with diabetes based on impaired fasting glucose levels alone, only 46% had 2 h postprandial concentrations that met the WHO postprandial glucose criterion.
Based on the ability to predict mortality, evidence supports the need to measure postprandial glucose levels for diabetes risk assessment in asymptomatic individuals. And so the next time your physician orders a diabetes check-up make sure that he is looking at the right sugar levels.