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Are European standard deviation targets for haemoglobin A1c too strict?
E S Kilpatrick1, W S Kilpatrick, M H Dominiczak
1Department of Clinical Biochemistry, Hull Royal Infirmary, UK.
Insights
Classifying glycemic control using standard deviations (SD) may overestimate targets for Type 1 diabetes patients. Standardizing to Diabetes Control and Complications Trial (DCCT) targets is more appropriate for managing HbA1c levels.
Area of Science:
- Endocrinology
- Metabolic Diseases
- Clinical Research
Background:
- The Diabetes Control and Complications Trial (DCCT) established desirable glycemic control targets for Type 1 diabetes using hemoglobin A1c (HbA1c).
- Variations in HbA1c assays have led to alternative classification methods, such as using standard deviations (SD) from a non-diabetic mean.
- Accurate assessment of glycemic control is crucial for preventing microvascular complications in Type 1 diabetes.
Purpose of the Study:
- To compare the classification of glycemic control in UK Type 1 diabetic patients using DCCT targets versus the SD method.
- To evaluate the appropriateness of SD-based guidelines for assessing glycemic control in Type 1 diabetes.
- To determine if SD-based guidelines overestimate the glycemic control needed to reduce complications.
Main Methods:
- Glycemic control of 339 UK Type 1 diabetic patients was assessed using DCCT targets.
- A comparison was made with classification based on SD from a local non-diabetic population mean (n=106).
- HbA1c results were calibrated to the DCCT analyzer.
Main Results:
- SD guidelines classified 95% of patients as having poor glycemic control (<3SD from reference mean).
- When calibrated to DCCT, 37% of patients had HbA1c <7% (DCCT intensive treatment median), and 71% had HbA1c <8% (associated with DCCT intensive treatment).
- SD-based classification significantly differed from DCCT target-based assessment.
Conclusions:
- Guidelines based on SD from a non-diabetic mean may overestimate the glycemic control required for Type 1 diabetes.
- Standardizing HbA1c assessment to DCCT targets is more appropriate for evaluating glycemic control and guiding treatment in Type 1 diabetes.
- This approach better reflects the glycemic control achieved in intensively treated DCCT subjects.
Abstract:
The Diabetes Control and Complications Trial (DCCT) has provided objective evidence for desirable glycaemic control in Type 1 patients and defines the benefits of good glycaemic control in terms of haemoglobin A1c (HbA1c) values. However, HbA1c assays vary, leading to suggestions that glycaemic control be classified according to numbers of standard deviations (SD) from a local non-diabetic population mean. We have classified the glycaemic control of 339 UK Type 1 diabetic patients (182 male, 157 female, median age 36 (range 15-74) years) using the DCCT to set HbA1c targets and compared this with the SD method. Using age matched controls (mean HbA1c 4.02%, SD 0.28%, n=106), SD guidelines classified 1% of patients into good (HbA1c <3SD from reference mean), 4% into borderline (3-5SD) and 95% into poor (>5SD) glycaemic control. When calibrating the same instrument to the DCCT analyser (r=0.996), 37% of patients had HbA1c results lower than the 7% median value found in the intensively treated DCCT group, while only 12% of patients had values greater than the 9% conventionally treated median HbA1c. DCCT subjects with HbA1c values of less than 8% belonged predominantly to the intensively treated group. In this study, 71% of patients fell into this category. Thus, guidelines based on numbers of SD away from a non-diabetic mean may overestimate the glycaemic control required to reduce microvascular complications in Type 1 patients. Standardizing to DCCT targets is more appropriate.