Fasting and two-hour post-load glucose levels for the diagnosis of diabetes

Abstract

The frequency distributions of both the fasting and two-hour post-load plasma glucose levels were bimodal in the Pima Indian population aged 25 years and over. The hyperglycaemic component of this distribution represents those with diabetes mellitus, as some 30 percent of this group had evidence of the specific vascular complications of the disease, whereas these abnormalities were virtually absent in those with lower glucose levels. The bimodal characteristics of the frequency distributions were utilized to define optimal criteria to separate those with and without diabetes. The sensitivity and specificity of these criteria for fasting and two-hour glucose levels were compared and were found to be similar. The fasting glucose determination, however, was more reproducible and stable, as well as being easier to obtain, indicating that it is the better measurement for diagnostic purposes. The optimal level for diagnosis of 7.5 mmol/l (136 mg/dl) for the fasting glucose and the equivalent two-hour value of 14 mmol/l (250 mg/dl), were higher than many previously recommended diagnostic levels. Nevertheless, there was no evidence that subjects with lower levels were at appreciable risk of developing the specific complications of diabetes. Subjects with impaired glucose tolerance (IGT), but without fasting hyperglycaemia, should not be diagnosed as having diabetes mellitus.

International Expert Committee Report on the Role of the A1C Assay in the Diagnosis of Diabetes

“…Studies in the high-risk Pima Indian population that demonstrated a bimodal distribution of glucose levels following the OGTT (7,8) helped establish the 2-h value as the diagnostic value of choice, even though most populations had a unimodal distribution of glucose levels (9). Of note, a bimodal distribution was also seen in the fasting glucose samples in the Pimas and other high-risk populations (10,11). However, a discrete fasting plasma glucose (FPG) or 2-h plasma glucose (2HPG) level that separated the bimodal distributions in the Pimas was difficult to identify, with potential FPG and 2HPG cut points ranging from 120 to 160 mg/dl (6.7–8.9 mmol/l) and from 200 to 250 mg/dl (11.1–13.9 mmol/l), respectively.…”

“…The NDDG relied on distributions of glucose levels, rather than on the relationship of glucose levels with complications, to diagnose diabetes despite emerging evidence that the microvascular complications of diabetes were associated with a higher range of fasting and OGTT glucose values (11,13–15). The diagnostic glucose values chosen were based on their association with decompensation to “overt” or symptomatic diabetes.…”

Predictive Value of Albuminuria in American Indian Youth With or Without Type 2 Diabetes

“…The bimodality of plasma glucose, first described in this population [37], combined with the presence of retinopathy and nephropathy among those in the upper component of the distribution [38] led to standardized criteria for the diagnosis of diabetes adopted by the National Diabetes Data Group [39], the World Health Organization [16, 40], and the American Diabetes Association [41]. In the Diabetes Prevention Program [42], a clinical trial of diabetes prevention, Southwestern American Indians (many of whom were Pima), had the same risk of type 2 diabetes and the same reductions in risk from the interventions as members of other race/ethnic groups.…”

Using HbA1c to Improve Efficacy of the American Diabetes Association Fasting Plasma Glucose Criterion in Screening for New Type 2 Diabetes in American Indians

“…Such discrepancies will reduce the efficacy of using FPG alone in diabetes screening. It is difficult to get physicians and patients to use the oral glucose tolerance test (OGTT) because of its drawbacks (12)(13)(14)(15)(16), especially for those patients already having an FPG Ͻ126. It is also impractical to conduct the OGTT for everyone in a diabetes screening.…”