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Area-under-the-HbA1c-curve above the normal range and the prediction of microvascular outcomes: an analysis of data from the Diabetes Control and Complications Trial

Authors

  • L. J. Maple-Brown,

    1. Leadership Sinai Centre for Diabetes, Mount Sinai Hospital, Toronto, ON, Canada
    2. Menzies School of Health Research, Charles Darwin University
    3. Division of Medicine, Royal Darwin Hospital, Darwin, NT, Australia
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  • C. Ye,

    1. Leadership Sinai Centre for Diabetes, Mount Sinai Hospital, Toronto, ON, Canada
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  • R. Retnakaran

    1. Leadership Sinai Centre for Diabetes, Mount Sinai Hospital, Toronto, ON, Canada
    2. Division of Endocrinology, University of Toronto, Toronto, ON, Canada
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Ravi Retnakaran. E-mail: rretnakaran@mtsinai.on.ca

Abstract

Aims  In the Diabetes Control and Complications Trial, mean updated HbA1c accounted for most of the differential risk of microvascular complications between intensive and conventional insulin therapy. We hypothesized, however, that a more precise measure of chronic hyperglycaemic exposure may be the incremental area-under-the-HbA1c-curve above the Diabetes Control and Complications Trial-standardized normal range for HbA1c (iAUCHbA1c>norm).

Methods  Using the Principal Diabetes Control and Complications Trial data set, we compared the following three measures of chronic glycaemic exposure for their capacity to predict retinopathy, nephropathy and neuropathy during the Diabetes Control and Complications Trial: mean updated HbA1c, iAUCHbA1c>norm, and total area-under-the-HbA1c-curve (tAUCHbA1c). For each outcome, models using each of these three glycaemic measures were compared in the following three ways: hazard or odds ratio, χ2 statistic, and Akaike information criterion.

Results  The three glycaemic measures did not differ in their prediction of neuropathy. iAUCHbA1c>norm was modestly superior to mean updated HbA1c for predicting nephropathy (χ2P = 0.017, Akaike P = 0.032). In contrast, for predicting retinopathy, both iAUCHbA1c>norm2P = 0.0005, Akaike P = 0.0005) and tAUCHbA1c2P = 0.004, Akaike P = 0.004) were significantly better than mean updated HbA1c. Varying its HbA1c threshold incrementally between 37 and 53 mmol/mol (5.5–7.0%), inclusive, did not improve the prediction of retinopathy by iAUCHbA1c>threshold beyond that of tAUCHbA1c,consistent with the concept of a continuous relationship between glycaemia and retinopathy, with no glycaemic threshold.

Conclusions  Both iAUCHbA1c>norm and tAUCHbA1c were superior to mean updated HbA1c for predicting retinopathy. Optimal assessment of chronic glycaemic exposure as a determinant of retinopathic risk may require consideration of both the degree of hyperglycaemia and its duration.

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