The effect of elevated fetal hemoglobin on hemoglobin A1c results: five common hemoglobin A1c methods compared with the IFCC reference method.

Hemoglobin A1c (HbA1c) is an important indicator of risk for complications in patients with diabetes mellitus. Elevated fetal hemoglobin (HbF) levels have been reported to interfere with results of some HbA1c methods, but it has generally been assumed that HbA1c results from boronate-affinity methods are not affected by elevated HbF levels. None of the previous studies used the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference method as the comparative HbA1c method. We, therefore, measured HbA1c in samples with normal and elevated HbF levels by several common assay methods and compared the results with those of the IFCC reference method.HbF levels of more than 20% artificially lowered HbA1c results from the Primus CLC 330/385 (Primus Diagnostics, Kansas City, MO), Siemens DCA2000 (Siemens Healthcare Diagnostics, Tarrytown, NY), and Tosoh 2.2+ (Tosoh Bioscience, South San Francisco, CA), but not the Bio-Rad Variant II (Bio-Rad Laboratories, Hercules, CA) and Tosoh G7. Physicians and laboratory professionals need to be aware of potential interference from elevated HbF levels that could affect HbA1c results, including those from boronate-affinity methods.

Defining the relationship between plasma glucose and HbA(1c): analysis of glucose profiles and HbA(1c) in the Diabetes Control and Complications Trial.

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 = 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). RESULTS: Linear regression analysis, using MPG and HbA(1c) summarized by patient (n = 1,439), produced a relationship of MPG (mmol/l) = (1.98 . HbA(1c)) - 4.29 or MPG (mg/dl) = (35.6 . HbA(1c)) - 77.3, r = 0.82). Among individual time points, afternoon and evening PG (postlunch, predinner, postdinner, and bedtime) showed higher correlations with HbA(1c) than the morning time points (prebreakfast, postbreakfast, and prelunch). 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.