Glycated haemoglobin assays. Approaches to standardization of results

To compare different approaches to DCCT standardization of glycated haemoglobin (HbA(1c)) results.

In the first part of the study seven laboratories in the Mersey area participated, using a variety of methods of measurement. The approaches used were the Standardization Initiative for Glycated Haemoglobin Scheme (SIGH) using fresh blood samples and the Wales External Quality Assurance Scheme (WEQAS) using both fresh and lyophilized blood samples. Additional studies performed in the Royal Liverpool University Hospital (RLUH) laboratory involved: (i) re-calibration of the HPLC analyser using lyophilized blood samples supplied by the manufacturer and (ii) the use of fresh blood samples from the UK National External Quality Assurance Scheme (UKNEQAS).

Inter-laboratory analytical coefficients of variation following DCCT alignment showed little change. The effect on percentage bias was more marked and was independent of the level of HbA(1c). Comparing DCCT-aligned HbA(1c) results from 3902 diabetic patients attending the RLUH, indicated that there was a statistically significant difference (P < 0.0001) between the corrected results produced by the five schemes. The effect of DCCT alignment on reported HbA(1c) values using the different approaches was variable resulting in an apparent increase in the number of diabetic patients with poor glycaemic control (HbA(1c) values > 7.0%) in all cases.

The method of HbA1c standardization used determines the degree of correction required and a consensus approach is recommended. Implementation will assist extrapolation from research-based evidence to local practice. Associated changes to patient management must come under the jurisdiction of the physicians responsible for the diabetic service.