Association of HbA1c Values with Mortality and Cardiovascular Events in Diabetic Dialysis Patients. The INVOR Study and Review of the Literature

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Abstract
Improved glycemic control reduces complications in patients with diabetes mellitus (DM). However, it is discussed controversially whether patients with diabetes mellitus and end-stage renal disease benefit from strict glycemic control. We followed 78 patients with DM initiating dialysis treatment of the region of Vorarlberg in a prospective cohort study applying a time-dependent Cox regression analysis using all measured laboratory values for up to more than seven years. This resulted in 880 HbA1c measurements (with one measurement every 3.16 patient months on average) during the entire observation period. Non-linear P-splines were used to allow flexible modeling of the association with mortality and cardiovascular disease (CVD) events. We observed a decreased mortality risk with increasing HbA1c values (HR = 0.72 per 1% increase, p = 0.024). Adjustment for age and sex and additional adjustment for other CVD risk factors only slightly attenuated the association (HR = 0.71, p = 0.044). A non-linear P-spline showed that the association did not follow a fully linear pattern with a highly significant non-linear component (p = 0.001) with an increased risk of all-cause mortality for HbA1c values up to 6–7%. Causes of death were associated with HbA1c values. The risk for CVD events, however, increased with increasing HbA1c values (HR = 1.24 per 1% increase, p = 0.048) but vanished after extended adjustments. This study considered the entire information collected on HbA1c over a period of more than seven years. Besides the methodological advantages our data indicate a significant inverse association between HbA1c levels and all-cause mortality. However, for CVD events no significant association could be found.

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