Investigation of 2 Models to Set and Evaluate Quality Targets for Hb A1c: Biological Variation and Sigma-Metrics

Abstract

Background A major objective of the IFCC Task Force on implementation of HbA1c standardization is to develop a model to define quality targets for HbA1c. Methods Two generic models, the Biological Variation and Sigma-metrics model, are investigated. Variables in the models were selected for HbA1c and data of EQA/PT programs were used to evaluate the suitability of the models to set and evaluate quality targets within and between laboratories. Results In the biological variation model 48% of individual laboratories and none of the 26 instrument groups met the minimum performance criterion. In the Sigma-metrics model, with a total allowable error (TAE) set at 5 mmol/mol (0.46% NGSP) 77% of the individual laboratories and 12 of 26 instrument groups met the 2 sigma criterion. Conclusion The Biological Variation and Sigma-metrics model were demonstrated to be suitable for setting and evaluating quality targets within and between laboratories. The Sigma-metrics model is more flexible as both the TAE and the risk of failure can be adjusted to requirements related to e.g. use for diagnosis/monitoring or requirements of (inter)national authorities. With the aim of reaching international consensus on advice regarding quality targets for HbA1c, the Task Force suggests the Sigma-metrics model as the model of choice with default values of 5 mmol/mol (0.46%) for TAE, and risk levels of 2 and 4 sigma for routine laboratories and laboratories performing clinical trials, respectively. These goals should serve as a starting point for discussion with international stakeholders in the field of diabetes.

Useful measures and models for analytical quality management in medical laboratories

“…On average, bias consumed about a third of the 6.0% ATE budget and for some examination subgroups consumed the entire error budget. Similar biases were observed by Weykamp et al [46] in their recent investigation and evaluation of targets for HbA 1c based on sigma-metrics and biologic variation.…”

Performance of point-of-care HbA1ctest devices: implications for use in clinical practice – a systematic review and meta-analysis

“…More recently, the IFCC Task Force on HbA 1c Standardization have recommended using a sigma metrics approach to evaluating analytical error. This takes into account both bias and imprecision in one model based on total allowable error, where bias and imprecision are not treated as separate performance measures [81]. The CAP survey [80] includes data from HbA 1c POC devices and shows comparable performance to a number of routine laboratory analysers.…”

Evaluating new HbA1c methods for adoption by the IFCC and NGSP reference networks using international quality targets

“…The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Task Force on Implementation of HbA 1c standardization (TF-HbA 1c ) recently advocated sigma-metrics as the model of choice to set and evaluate quality targets for HbA 1c [4]. In the laboratory sigma-metrics is a quality management strategy that provides a universal benchmark for process performances.…”