title: A1C variability and the risk of microvascular complications in type 1 diabetes: data from the Diabetes Control and Complications Trial.
abstract: OBJECTIVE
  Debate remains as to whether short- or long-term glycemic instability confers a risk of microvascular complications in addition to that predicted by mean glycemia alone. In this study, we analyzed data from the Diabetes Control and Complications Trial (DCCT) to assess the effect of A1C variability on the risk of retinopathy and nephropathy in patients with type 1 diabetes.
  
  
  METHODS
  A1C was collected quarterly during the DCCT in 1,441 individuals. The mean A1C and the SD of A1C variability after stabilization of glycemia (from 6 months onwards) were compared with the risk of retinopathy and nephropathy with adjustments for age, sex, disease duration, treatment group, and baseline A1C.
  
  
  RESULTS
  Multivariate Cox regression showed that the variability in A1C added to mean A1C in predicting the risk of development or progression of both retinopathy (hazard ratio 2.26 for every 1% increase in A1C SD [95% CI 1.63-3.14], P < 0.0001) and nephropathy (1.80 [1.37-2.42], P < 0.0001), with the relationship a feature in conventionally treated patients in particular.
  
  
  CONCLUSIONS
  This study has shown that variability in A1C adds to the mean value in predicting microvascular complications in type 1 diabetes. Thus, in contrast to analyses of DCCT data investigating the effect of short-term glucose instability on complication risk, longer-term fluctuations in glycemia seem to contribute to the development of retinopathy and nephropathy in type 1 diabetes.
authors.affiliation: Department of Clinical Biochemistry, Hull Royal Infirmary, Hull, UK. eric.kilpatrick@hey.nhs.uk
authors.forename: Eric S
authors.initials: ES
authors.lastname: Kilpatrick
authors.forename: Alan S
authors.initials: AS
authors.lastname: Rigby
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Atkin
mesh_terms: D003922:Diabetes Mellitus, Type 1 / Q000097:blood* / Q000150:complications / Q000517:prevention & control; D003929:Diabetic Neuropathies / Q000097:blood* / Q000209:etiology; D003930:Diabetic Retinopathy / Q000097:blood* / Q000209:etiology; D018450:Disease Progression; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D016016:Proportional Hazards Models; D018570:Risk Assessment / Q000706:statistics & numerical data; D012307:Risk Factors
chemical_list: D006442:Glycated Hemoglobin