Special Feature

Changes in the Criteria for the Diagnosis and Classification of Diabetes Mellitus

By Steven Gabbe, MD

In 1995, the american diabetes association (ada) convened an Expert Committee on the diagnosis and classification of diabetes mellitus. I was honored to serve as a member. In this special feature, I want to summarize the important changes in the Expert Committee report, emphasizing how they will affect patient care.1

The committee recommended that diabetes mellitus be classified based on its etiology.1 Type 1 diabetes mellitus results from b-cell destruction that is usually due to an autoimmune process and causes absolute insulin deficiency. In the past, this type of diabetes was known as insulin-dependent diabetes mellitus (IDDM) or type 1 diabetes. Type 2 mellitus is the most common form of diabetes in the United States and is characterized by insulin resistance with either a relative deficiency in insulin or an insulin secretory defect. This type of diabetes had been referred to as non-insulin-dependent diabetes mellitus (NIDDM) or type 2 diabetes. The committee recommended that Arabic numerals be used to avoid confusing the Roman numeral "II" with the Arabic number "11." Why discard the terms "insulin-" or "non-insulin-dependent" diabetes? Because many individuals with type 2 diabetes will benefit from treatment with insulin. If a patient were classified "non-insulin-dependent," health care providers might be reluctant to initiate this therapy.

The diagnosis of diabetes mellitus may be made in three ways, and each must be confirmed on a subsequent day: 1) a patient with symptoms whose random or "casual" plasma glucose is 200 mg/dL or higher; 2) a fasting plasma glucose of 126 mg/dL or higher; or 3) a two-hour glucose value of 200 mg/dL or higher as part of a 75 g oral glucose tolerance test. The committee recommended that the fasting plasma glucose cutoff for the diagnosis of diabetes that had been 140 mg/dL or higher be lowered so that it would be more in line with the two-hour post-load glucose of 200 mg/dL. Furthermore, using a fasting glucose to establish the diagnosis of diabetes is much easier in clinical practice. Both the fasting and the two-hour post-load glucose value recommended by the committee have been associated with significant vascular disease in large, population-based studies. It should be emphasized that these are not criteria for treatment, but rather for diagnosis.

It has been estimated that 50% of the more than 14 million individuals with type 2 diabetes in the United States are unrecognized. At the time of diagnosis, many patients with type 2 diabetes already have complications, meaning that they have had the disease for 10 years or more. Simplifying the screening process by using a fasting glucose may help to detect type 2 diabetes before vascular disease has occurred. The Committee recommended that all individuals who are age 45 or older be tested for diabetes mellitus using a fasting plasma glucose with a cutoff of 126 mg/dL or more. While a 75 g oral glucose tolerance test can be performed, the fasting plasma glucose is easier to do and much less expensive. If the patient has a normal fasting glucose, the test should be repeated at three-year intervals. Testing should be considered at a younger age or performed more frequently in those with any of the following: obesity, a first-degree relative with diabetes, member of a high-risk ethnic population such as blacks, Hispanics, or Native Americans; delivery of a baby weighing more than nine pounds; history of gestational diabetes mellitus; hypertension (> 140/90 mmHg), an HDL cholesterol level of 35 mg/dL or lower, and/or a triglyceride level 250 mg/dLor higher; or, on previous testing, an elevation of fasting glucose of 110 mg/dL or more but not exceeding 126 mg/dL (impaired fasting glucose); or, on the 75 g glucose tolerance test, a two-hour value of more than 140 mg/dL but less than 200 mg/dL (impaired glucose tolerance).

Gestational Diabetes Mellitus

In 1979, the National Diabetes Data Group (NDDG) also convened by the ADA established a separate classification, gestational diabetes mellitus (GDM).2 GDM "is restricted to pregnant women in whom the onset or recognition of diabetes or IGT (impaired glucose tolerance) occurs during pregnancy." This report noted that most women with GDM would return to normal glucose tolerance after delivery but that GDM was associated with an increased risk for perinatal morbidity and mortality. The criteria for abnormal glucose tolerance in pregnancy were based on studies by O’Sullivan and Mahan and were originally developed to select a population at increased risk for the development of diabetes later in life.3 The diagnosis of GDM was established if two or more of the following venous plasma values were met or exceeded after a 100 g oral glucose challenge: fasting, 105 mg/dL; one-hour, 190 mg/dL; two-hour, 165 mg/dL; and three-hour, 145 mg/dL. No recommendations on screening for GDM were made.

The Expert Committee used the definition recommended by the third International Workshop-Conference on GDM in 1991: "GDM is defined as any degree of glucose intolerance with onset or first recognition during pregnancy. The definition applies regardless of whether insulin or only diet modification is used for treatment or whether the condition persists after pregnancy. It does not exclude the possibility that unrecognized glucose intolerance may have antedated or begun concomitantly with the pregnancy."4 The O’Sullivan and Mahan criteria recommended in 1979 for the diagnosis of GDM were also supported by the Expert Committee.

While the third International Workshop Conference recommended that universal screening be adopted to detect GDM (see OB/GYN Clin Alert 1993;10:7-8), the Expert Committee emphasized that there are certain factors that place women at such low risk for GDM that it is not cost-effective to screen them. This low-risk group includes women who meet all of the following criteria: younger than 25 years of age; normal body weight; no family history of a first-degree relative with diabetes mellitus; and, not a member of an ethnic or racial group with a high prevalence of diabetes such as Hispanic, black, Native American, or Asian. The 50 g oral glucose load administered at 24-28 weeks gestation without regard to time of day or time of last meal with a plasma glucose determination one hour later was recommended. A value of 140 mg/dL or more indicates a positive screening test and the need for the 100 g three-hour oral glucose tolerance test. This strategy for screening is quite similar to that recommended by the American College of Obstetricians and Gynecologists in its 1994 Technical Bulletin that states, "Whereas selective screening for GDM (i.e., screening women with traditional risk factors) may be appropriate in some clinical settings such as teen clinics, universal screening may be more appropriate in other settings."5

Screening for diabetes mellitus in the postpartum period can be simplified, using a fasting plasma glucose level with normal values being 125 mg/dL or lower, as recommended by the Expert Committee.

References

1. The Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes Care 1997;7:1183-1197.

2. National Diabetes Data Group (NDDG). Classification and diagnosis of diabetes mellitus and other categories of glucose intolerance. Diabetes 1979;28:1039-1057.

3. O’Sullivan JM, Mahan CM. Criteria for the oral glucose tolerance test in pregnancy. Diabetes 1964;13:278.

4. Metzger BE, Organizing Committee. Summary and recommendations of the 3rd International Workshop-Conference on gestational diabetes mellitus. Diabetes 1997;40:197-201.

5. Diabetes and pregnancy. ACOG Technical Bulletin 1994;200.