Background: Since the DCCT demonstrated that improved glycaemic control reduced complications the goal of diabetes management has been to maintain HbA1c as close to normal as possible. Recent changes by the laboratory to our HbA1c assay, combined with the debate about deanonymised publication of clinics HbA1c results, creating the potential for league tables, focussed our attention on the variation between HbA1c assays.
Clinical data: Our local adult hospital, which previously processed our HbA1c specimens, opted to replace an aging analyser. During the evaluation of the new analyser, samples were run on both systems for a trial period. Our clinic average HbA1c on the existing analyser was 8.4% but rose 0.7 to 9.1% on the replacement. A few months later we introduced point of care testing and evaluated 3 different analysers. Despite all analysers being DCCT aligned, our clinic average was 8.9, 8.4 or 7.6% depending on the system!
Discussion: The international consensus within the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) on reference methods ensures that all currently available HbA1c assays are DCCT aligned. But what exactly does this mean? DCCT alignment is awarded if results are ±1% of the reference samples. Within the UKNEQAS programme (a quality control programme run by Birmingham to which UK accredited laboratories submit data) results for the 7.5% HbA1c standard vary from 6.9 to 8.3%; the difference between a clinic being promoted or relegated in a league table!
As NHS diabetes care focuses on outcomes HbA1c is often selected as the key indicator of quality. For GPs, of the 30 available Quality and Outcomes Framework (QOF) points for diabetes, 27 relate to glycaemic control. Each QOF point awards a GP an additional £168 income. Thus variation in HbA1c can make significant differences to incomes. The NCASP National Diabetes Audit already plots UK centres against each other, in an anonymised fashion, and it seems likely that centres will in future be named, generating league tables.
Conclusion: Further standardisation of HbA1c assays is required before it can be reliably used as a marker of quality of care to compare the performance of different centres and before payment is based on such metrics. Our clinic average varied from 7.6 to 9.1% dependent on the laboratory method. Which assay did we choose?…it was tempting!