HbA1c as the diagnostic criterion for diabetes reduces incidence and prevalence of DM2 by 25% but strongly depending on analytical quality
Ivan Brandslund1,*, Aneta Alexandra Nielsen2, Per Hyltoft Petersen3, Anders Green4, Cramer Kjeldahl Christensen5, Henry Christensen6
1Institute of Regional Health Research, University of Southern Denmark, Odense, 2Clinical Immunology and Biochemestry, Lillebaelt Hospital, Kolding, Denmark, 3NOKLUS Norwegian quality improvement of primary care laboratories, Division for General Practice, University of Bergen, Bergen, Norway, 4Patient data Explorative Network (OPEN), University of Southern Denmark, Odense, 5Medical Department, Lillebælt Hospital, 6Clinical Immunology and Biochemistry, Lillebalt Hospital, Vejle, Denmark
Introduction: In Denmark, the use of HbA1c in the diagnosis of diabetes was adopted from March 2012.
Objectives: To evaluate the change in the number of diabetes cases diagnosed by haemoglobin A1c (hbA1c) versus fasting venous plasma glucose (FPG), and estimate the influence of analytical variation and bias on the HbA1c –based prevalence of diabetes.
Methods: The study population constituted 4,239 individuals not known to have diabetes randomly selected from all inhabitants aged 25-75 years in the former County of Vejle, Denmark. The number of undiagnosed patients with diabetes in the study population using FPG or HbA1c as the diagnostic criterion was estimated. Furthermore, changes in the analytical bias and coefficient of variation (CV) for HbA1c analysis were simulated and the effect on the number of diabetes cases was observed.
Results: Changing the diagnostic test from FPG to HbA1c reduced the number of patients with diabetes by approximately 46% based on one measurement, but 25% using a confirmatory second test. The predictive value of one test of HbA1c was 91% versus only 66% for one test of FPG. Analytical variation of HbA1c had a much greater impact on the number of patients with diabetes than bias. At a bias of 0%, an increase of CVanalytical from 2.7% to 3.7% increased the number of diabetes cases by 90%, and an increase in bias to +5% by 40%.
Conclusion: When using HbA1c for diagnosis of Diabetes Type 2 the analytical quality maintaining a bias below +/- 2.8% and an analytical CV below 2.8% is crucial for the number of diabetes patients identified.
In this way the laboratory’s important role in the diagnostic process of this serious disease is emphasized.
The core task for the clinical laboratory is the producing of reliable analytical results and the ability at any time to be able to document that clinical needs are fulfilled.