Hsiao-Mei Wiedmeyer

Prevalence of Diabetes, Impaired Fasting Glucose, and Impaired Glucose Tolerance in U.S. Adults: The Third National Health and Nutrition Examination Survey, 1988–1994

OBJECTIVE To evaluate the prevalence and time trends for diagnosed and undiagnosed diabetes, impaired fasting glucose, and impaired glucose tolerance in U.S. adults by age, sex, and race or ethnic group, based on data from the Third National Health and Nutrition Examination Survey, 1988–1994 (NHANES 111) and prior Health and Nutrition Examination Surveys (HANESs). RESEARCH DESIGN AND METHODS NHANES III contained a probability sample of 18,825 U.S. adults ≥20 years of age who were interviewed to ascertain a medical history of diagnosed diabetes, a subsample of 6,587 adults for whom fasting plasma glucose values were obtained, and a subsample of 2,844 adults between 40 and 74 years of age who received an oral glucose tolerance test. The Second National Health and Nutrition Examination Survey, 1976–1980, and Hispanic HANES used similar procedures to ascertain diabetes. Prevalence was calculated using the 1997 American Diabetes Association fasting plasma glucose criteria and the 1980–1985 World Health Organization (WHO) oral glucose tolerance test criteria. RESULTS Prevalence of diagnosed diabetes in 1988–1994 was estimated to be 5.1% for U.S. adults ≥20 years of age (10.2 million people when extrapolated to the 1997 U.S. population). Using American Diabetes Association criteria, the prevalence of undiagnosed diabetes (fasting plasma glucose ≥126 mg/dl) was 2.7% (5.4 million), and the prevalence of impaired fasting glucose (110 to <126 mg/dl) was 6.9% (13.4 million). There were similar rates of diabetes for men and women, but the rates for non-Hispanic blacks and Mexican-Americans were 1.6 and 1.9 times the rate for non-Hispanic whites. Based on American Diabetes Association criteria, prevalence of diabetes (diagnosed plus undiagnosed) in the total population of people who were 40–74 years of age increased from 8.9% in the period 1976–1980 to 12.3% by 1988–1994. A similar increase was found when WHO criteria were applied (11.4 and 14.3%). CONCLUSIONS The high rates of abnormal fasting and postchallenge glucose found in NHANES III, together with the increasing frequency of obesity and sedentary lifestyles in the population, make it likely that diabetes will continue to be a major health problem in the U.S

Clinical Application of Glycosylated Hemoglobin Measurements

Glycosylated hemoglobin measurement has been shown to be a potentially useful tool for both a variety of research applications and for the management of patients with diabetes mellitus. None of the methods available to quantitate glycosylated hemoglobins is ideal. We have reviewed a number of critical methodologie considerations for Chromatographie procedures including the effects of sample storage under various conditions, and the importance of removing labile components prior to analyses. We have developed a method for the colorimetrie determination of glycosylated hemoglobins that is more rapid than methods reported previously, that correlates well with results using high-performance liquid chromatogra-phy, and that can he standardized between laboratories. We have reviewed our experience using glycosylated hemoglobin in a large population of diabetic youths. We have presented a method for developing realistic goals for glucose control using glycosylated hemoglobin and for using glycosylated hemoglobin as a patient education and care reinforcement tool.

Relationship of Glycosylated Hemoglobin to Oral Glucose Tolerance: Implications for Diabetes Screening

The oral glucose tolerance test (OGTT) for diagnosis of diabetes is inconvenient and requires a great deal of patient cooperation. Glycosylated hemoglobin (GHb), an index of long-term glycemic control, could offer several practical advantages over the OGTT for diabetes screening. We evaluated GHb as a screen for diabetes in 381 adults from a population with a high prevalence of non-insulin-dependent diabetes (Pima Indians). All individuals underwent a standard OGTT (75 g) and were separated into one of three groups: normal (N), impaired glucose tolerance (IGT), or diabetes mellitus (D) based on World Health Organization criteria. HbA1c, a GHb, was measured by highly precise high-performance liquid chromatography (interassay C.V. <4%). The normal range for HbA1c was 4.07–6.03% based on the 95% confidence interval for a nondiabetic, mostly Caucasian population. Compared with OGTT, HbA1c was highly specific (91%); an elevated HbA1c usually indicated D or IGT (sensitivity = 85 and 30%, respectively). A normal HbA1c did not, however, exclude a diagnosis of D or IGT. Based on previous epidemiological studies relating plasma glucose to chronic diabetic complications, GHb as measured in this study would properly identify the vast majority of subjects at risk. Long-term studies are necessary to determine the actual risk of complications in individuals with persistently normal HbA1c and D or IGT (based on OGTT).

Glycated haemoglobin predicts progression to diabetes mellitus in Pima Indians with impaired glucose tolerance

SummaryGlycated haemoglobin could offer several practical advantages over the OGTT for assessing glucose metabolism. Initial cross-sectional studies (1983–1985) on 381 subjects (mostly Pima Indians) described the relationship between HbA1c (a specific glycated Hb) and the OGTT. We performed follow-up OGTTs and HbA1c measurements on 257 of these same subjects 1.6–6.1 years later. Subjects were again grouped according to both the result of the OGTT (normal, IGT or diabetes, by WHO criteria) and HbA1c result (normal or elevated based on mean ± 1.96 SD of normal). Of 66 subjects with IGT at baseline, 47 (71%) had normal HbA1c and 19 (29%) had elevated HbA1c. Twentysix (39%) of these subjects had diabetes at follow-up. Of these subjects with IGT, a significantly greater percentage of subjects with elevated HbA1c at baseline (68%) showed worsening to diabetes than those with a normal HbA1c (28%); (chi-square=7.8, df=1, p<0.01). Thus, in subjects with IGT, glycated Hb may be a useful predictor of progression to diabetes.

Recent advances in glycosylated hemoglobin measurements

Glycosylated hemoglobins have gained wide acceptance as an accurate index of long-term blood glucose control in diabetes mellitus. A variety of glycosylated hemoglobin assays is available. There is a high degree of correlation between results determined by these assays. The ideal laboratory method for measuring glycosylated hemoglobin in the diabetic should be accurate, precise, easily standardized, inexpensive, and rapidly performed. Unfortunately, none of the currently used methods meet all of the criteria necessary to be considered the ideal laboratory method. The most widely used methods for quantitating glycosylated hemoglobins--including ion exchange chromatography, electrophoresis, isoelectric focusing, thiobarbituric acid colorimetry, and affinity chromatography--are reviewed with respect to the important advantages and disadvantages of each method for the clinical laboratory. Techniques for quantitating glycosylated proteins other than hemoglobins, such as albumin, are also discussed.

Statistical Rules for Laboratory Networks

Within the definition of reference methods, laboratory networks and interlaboratory studies play an important role.To maintain the quality of the results statistical rules for quality control need to be defined. In this note we review statistical rules for the evaluation of laboratories participating in interlaboratory studies as well as data evaluation rules for the calculation of consensus means.The practicality of the derived rules is elaborated for a number of recent HbA1c interlaboratory studies