OBJECTIVE -To define the relationship between HbA 1c and plasma glucose (PG) levels in patients with type 1 diabetes using data from the Diabetes Control and Complications Trial (DCCT).RESEARCH DESIGN AND METHODS -The DCCT was a multicenter, randomized clinical trial designed to compare intensive and conventional therapies and their relative effects on the development and progression of diabetic complications in patients with type 1 diabetes. Quarterly HbA 1c and corresponding seven-point capillary blood glucose profiles (premeal, postmeal, and bedtime) obtained in the DCCT were analyzed to define the relationship between HbA 1c and PG. Only data from complete profiles with corresponding HbA 1c were used (n ϭ 26,056). Of the 1,441 subjects who participated in the study, 2 were excluded due to missing data. Mean plasma glucose (MPG) was estimated by multiplying capillary blood glucose by 1.11. Linear regression analysis weighted by the number of observations per subject was used to correlate MPG and HbA 1c . CONCLUSIONS -We have defined the relationship between HbA 1c and PG as assessed in the DCCT. Knowing this relationship can help patients with diabetes and their healthcare providers set day-to-day targets for PG to achieve specific HbA 1c goals. RESULTS Diabetes Care 25:275-278, 2002

O B J E C T I V E -To evaluate the use of GHb as a screening test for undiagnosed diabetes (fasting plasma glucose 7.0 mmol/l) in a re p resentative sample of the U.S. population. RESEARCH DESIGN AND METHODS -The Third National Health and NutritionExamination Survey included national samples of non-Hispanic whites, non-Hispanic blacks, and Mexican Americans aged 20 years. Of these subjects, 7,832 participated in a morn i n g examination session, of which 1,273 were excluded because of a previous diagnosis of diabetes, missing data, or fasting time of 8 h before examination. Venous blood was obtained to meas u re fasting plasma glucose and GHb in the remaining 6,559 subjects. Receiver operating characteristic curve analysis was used to examine the sensitivity and specificity of GHb for detecting diabetes at increasing GHb cutoff levels. R E S U LT S -GHb demonstrated high sensitivity (83.4%) and specificity (84.4%) for detecting undiagnosed diabetes at a GHb cutoff of 1 SD above the normal mean. Moderate sensitivity (63.2%) and very high specificity (97.4%) were evident at a GHb cutoff of 2 SD above the n o rmal mean. Sensitivity at this level ranged from 58.6% in the non-Hispanic white population to 83.6% in the Mexican-American population; specificity ranged from 93.0% in the nonHispanic black population to 98.3% in the non-Hispanic white population.C O N C L U S I O N S -GHb is a highly specific and convenient alternative to fasting plasma glucose for diabetes screening. A GHb value of 2 SD above the normal mean could identify a high pro p o rtion of individuals with undiagnosed diabetes who are at risk for developing diabetes complications.

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Hemoglobin A1c (HbA1c) is a stable minor Hb variant formed in vivo by posttranslational modification by glucose, originally identified by using cation exchange chromatography, and containing primarily glycated N-terminal β-chains. However, the structure(s) of the quantified species has not been elucidated, and the available methods lack a reference standard. We used electrospray ionization mass spectrometry to determine the extent of glycation of samples separated by boronate affinity and/or cation exchange chromatography. Analyses of clinical samples were consistent with the curvilinear relationship of patient glucose and HbA1c. As glycation increased, the ratio of β-chain to α-chain glycation increased, and the number of glycation sites on the β-chain increased, although these were relatively minor components. We found several glycated species that cochromatographed with HbA1c on cation exchange, including species with both glycated α- and β-chains, nonglycated α- and glycated β-chains, and multiply glycated β-chains. The combined use of affinity and cation exchange chromatography with structural confirmation by electrospray ionization mass spectrometry was found to be useful in producing samples of sufficient purity for the standardization of glycohemoglobin clinical assays.

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