title: Reduced testing frequency for glycated hemoglobin, HbA1c, is associated with deteriorating diabetes control.
abstract: OBJECTIVE
  We previously showed that in patients with diabetes mellitus, glycated hemoglobin (HbA1c) monitoring outside international guidance on testing frequency is widespread. Here we examined the relationship between testing frequency and diabetes control to test the hypothesis that retest interval is linked to change in HbA1c level.
  
  
  METHODS
  We examined repeat HbA1c tests (400,497 tests in 79,409 patients, 2008-2011) processed by three U.K. clinical laboratories. We examined the relationship between retest interval and 1) percentage change in HbA1c and 2) proportion of cases showing a significant HbA1c rise. The effect of demographics factors on these findings was also explored.
  
  
  RESULTS
  Our data showed that the optimal testing frequency required to maximize the downward trajectory in HbA1c was four times per year, particularly in those with an initial HbA1c of ≥7% (≥53 mmol/mol), supporting international guidance. Testing 3-monthly was associated with a 3.8% reduction in HbA1c compared with a 1.5% increase observed with annual testing; testing more frequently provided no additional benefit. Compared with annual monitoring, 3-monthly testing was associated with a halving of the proportion showing a significant rise in HbA1c (7-10 vs. 15-20%).
  
  
  CONCLUSIONS
  These findings provide, in a large, multicenter data set, objective evidence that testing outside guidance on HbA1c monitoring frequency is associated with a significant detrimental effect on diabetes control. To achieve the optimum downward trajectory in HbA1c, monitoring frequency should be quarterly, particularly in cases with suboptimal HbA1c. While this impact appears small, optimizing monitoring frequency across the diabetes population may have major implications for diabetes control and comorbidity risk.
authors.affiliation: Department of Clinical Biochemistry, University Hospital of North Staffordshire National Health Service Trust, Stoke-on-Trent, Staffordshire, U.K. Institute of Science and Technology in Medicine, University of Keele, Stoke-on-Trent, Staffordshire, U.K.
authors.forename: Owen J
authors.initials: OJ
authors.lastname: Driskell
authors.affiliation: National Pathology Benchmarking Service, Department of Medicines Management, Keele University, Staffordshire, U.K.
authors.forename: David
authors.initials: D
authors.lastname: Holland
authors.affiliation: Department of Clinical Biochemistry, Royal Wolverhampton National Health Service Trust, Wolverhampton, U.K.
authors.forename: Jenna L
authors.initials: JL
authors.lastname: Waldron
authors.affiliation: Department of Clinical Biochemistry, Royal Wolverhampton National Health Service Trust, Wolverhampton, U.K.
authors.forename: Clare
authors.initials: C
authors.lastname: Ford
authors.affiliation: Department of Clinical Biochemistry, Salford Royal Hospital National Health Service Foundation Trust, U.K.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Scargill
authors.affiliation: Department of Clinical Biochemistry, Salford Royal Hospital National Health Service Foundation Trust, U.K. School of Medicine and Manchester Academic Health Sciences Centre, University of Manchester, Manchester, U.K.
authors.forename: Adrian
authors.initials: A
authors.lastname: Heald
authors.affiliation: Department of Clinical Biochemistry, University Hospital of North Staffordshire National Health Service Trust, Stoke-on-Trent, Staffordshire, U.K.
authors.forename: Martin
authors.initials: M
authors.lastname: Tran
authors.affiliation: Department of Clinical Biochemistry, University Hospital of North Staffordshire National Health Service Trust, Stoke-on-Trent, Staffordshire, U.K. Department of Diabetes and Endocrinology, University Hospital of North Staffordshire National Health Service Trust, Stoke-on-Trent, Staffordshire, U.K.
authors.forename: Fahmy W
authors.initials: FW
authors.lastname: Hanna
authors.affiliation: Institute of Science and Technology in Medicine, University of Keele, Stoke-on-Trent, Staffordshire, U.K. School of Computing and Mathematics, Keele University, Keele, Staffordshire, U.K.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Jones
authors.affiliation: Diabetes UK, North Staffordshire Branch, Newcastle-under-Lyme, Staffordshire, U.K.
authors.forename: R John
authors.initials: RJ
authors.lastname: Pemberton
authors.affiliation: Department of Clinical Biochemistry, University Hospital of North Staffordshire National Health Service Trust, Stoke-on-Trent, Staffordshire, U.K. Institute of Science and Technology in Medicine, University of Keele, Stoke-on-Trent, Staffordshire, U.K. anthony.fryer@uhns.nsh.uk.
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Fryer
mesh_terms: D000368:Aged; D015190:Blood Glucose Self-Monitoring / Q000706:statistics & numerical data; D015897:Comorbidity; D003920:Diabetes Mellitus / Q000097:blood* / Q000188:drug therapy*; D018450:Disease Progression; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D010349:Patient Compliance / Q000706:statistics & numerical data*
chemical_list: D006442:Glycated Hemoglobin