Stricter Guidelines for Diagnosing 'Pre-Diabetes'

Summarized by Robert W. Griffith, MD
January 29, 2004

Introduction

There are two main tests used in the diagnosis of diabetes as well as for lesser degrees of impaired glucose regulation. They are:

• Fasting plasma glucose (FPG) - measured in the morning after an overnight fast
• 2-hour plasma glucose (2-h PG) - measured 2 hours after a drink containing 75 grams of glucose

The first major recommendations for standardizing the diagnosis of diabetes were issued in 1976. In 1997 an International Expert Committee reviewed the limits for normal and abnormal results for these tests, lowering the criteria in most cases. Now a new expert committee has recommended that, while the criteria for diagnosing diabetes remain unchanged, the limits for what is considered 'normal' should be lowered. As a result, more people are likely to be found to have 'impaired glucose regulation'.

The levels have evolved over the years

Here are the criteria recommended by the three expert committees:

	1976	1997	2003
FPG - diagnosis of diabetes	140 mg/dl or over (7.8 mmol/L or over)	126 mg/dL or over (7.0 mmol/L)
FPG - normal levels	below 140 mg/dL (7.8 mmol/L)	below 110 mg/dL (6.1 mmol/L)	below 100 mg/dL (5.6 mmol/L)
2-h PG - diagnosis of diabetes		200 mg/dL or over (11.1 mmol/L)
2-h PG - normal levels		below 140 mg/dL (7.8 mmol/L)

The only change between the 1997 and 2003 guidelines concern the FPG level regarded as "normal". An FPG between 110 and 126 mg/dL used to be called "impaired fasting glucose", or IFG, but now the range is extended from 100 to 126 mg/dL.

Both IFG and impaired glucose tolerance (IGT - when the 2-h PG is above 140 but hasn't reached 200 mg/dL) are considered predictive for future development of diabetes. Individuals may have one, but not necessarily the other. This is because each measures a different metabolic state - one after a several-hour fast, the other the return toward normal levels within 2 hours of a meal. IGT is more common than IFG. Nevertheless, an FPG above 100 mg/dL is now regarded as a warning sign of possible trouble to come.

What's pre-diabetes?

It's commonly assumed that people with IFG and/or IGT are at high risk of developing diabetes (FGP over 126 mg/dL, or 2h-GP over 200 mg/dL). They are therefore often assigned the diagnosis "pre-diabetes". In some countries, pre-diabetics qualify for anti-diabetic drug therapy. Most important, however, is the realization that a significant change in lifestyle can effectively prevent the development of diabetes in such people.

What about glycated hemoglobin (HbA1c)?

Some authorities believe that the HbA1c level can be used to diagnose diabetes. This test, which is unaffected by food, can be measured at any time of day; it reflects the average amount of sugar in the blood over the previous 3 months or so. The expert committee concluded that the HbA1c was best used to monitor the effectiveness of diabetic therapy, indicating when treatment needs to be modified. It is not of proven value in actually diagnosing diabetes or pre-diabetes. Normal values of HbA1c are below 7%.

So what's new?

With the lowering of the normal level for FPG to 100 mg/dL, more people than before will be diagnosed as having pre-diabetes. But this isn't entirely bad news. A significant change in lifestyle - weight control by eating properly and exercising adequately - can prevent these persons progressing to full-blown diabetes, and thereby avoid the serious complications of this widespread disease.

Source

• Follow-up report on the diagnosis of diabetes mellitus.  The Expert Committee on the Diagnosis of Diabetes Mellitus., Diabetes Care, 2003, vol. 26, pp. 3160--3167

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