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

BACKGROUND: C-peptide is a marker of insulin secretion in diabetic patients. We assessed within-and between-laboratory imprecision of C-peptide assays and determined whether serum calibrators with values assigned by mass spectrometry could be used to harmonize C-peptide results.

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All methods either met or exceeded manufacturers' claims for stability. The CLC 385/330, Tosoh G7, and Bio-Rad Variant II high performance liquid chromatography methods showed better stability than the Tosoh 2.2 Plus and Bio-Rad Variant.

Background Carbamylated hemoglobin (carbHb) is reported to interfere with measurement and interpretation of HbA1c in diabetic patients with chronic renal failure (CRF). There is also concern that HbA1c may give low results in these patients due to shortened erythrocyte survival. Methods We evaluated the effect of carbHb on HbA1c measurements and compared HbA1c with glycated albumin (GA) in patients with and without renal disease to test if CRF causes clinically significant bias in HbA1c results using 11 assay methods. Subjects included those with and without renal failure and diabetes. Each subject’s estimated glomerular filtration rate (eGFR) was used to determine the presence and degree of renal disease. A multiple regression model was used to determine if the relationship between HbA1c results obtained from each test method and the comparative method were significantly (p<0.05) affected by eGFR. These methods were further evaluated for clinical significance using difference between the eGRF quartiles of >7% at 6 or 9% HbA1c. The relationship between HbA1c and glycated albumin (GA) in patients with and without renal failure was also compared. Results Some methods showed small but statistically significant effects of eGFR; none of these differences were clinically significant. If GA is assumed to better reflect glycemic control, then HbA1c was approximately 1.5% HbA1c lower in patients with renal failure. Conclusions Although most methods can measure HbA1c accurately in patients with renal failure, healthcare providers must interpret these test results cautiously in these patients due the propensity for shortened erythrocyte survival in renal failure.