Standardization of HbA1c measurements--a consensus statement

Glycated haemoglobin assays. Approaches to standardization of results

AIMS

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

METHODS

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).

RESULTS

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.

CONCLUSION

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.

Glycated haemoglobin, diabetes, and mortality in men in Norfolk cohort of european prospective investigation of cancer and nutrition (EPIC-Norfolk)

OBJECTIVE

To examine the value of glycated haemoglobin (HbA(1c)) concentration, a marker of blood glucose concentration, as a predictor of death from cardiovascular and all causes in men.

DESIGN

Prospective population study.

SETTING

Norfolk cohort of European Prospective Investigation into Cancer and Nutrition (EPIC-Norfolk).

SUBJECTS

4662 men aged 45-79 years who had had glycated haemoglobin measured at the baseline survey in 1995-7 who were followed up to December 1999.

MAIN OUTCOME MEASURES

Mortality from all causes, cardiovascular disease, ischaemic heart disease, and other causes.

RESULTS

Men with known diabetes had increased mortality from all causes, cardiovascular disease, and ischaemic disease (relative risks 2.2, 3.3, and 4.2, respectively, P <0.001 independent of age and other risk factors) compared with men without known diabetes. The increased risk of death among men with diabetes was largely explained by HbA(1c) concentration. HbA(1c) was continuously related to subsequent all cause, cardiovascular, and ischaemic heart disease mortality through the whole population distribution, with lowest rates in those with HbA(1c) concentrations below 5%. An increase of 1% in HbA(1c) was associated with a 28% (P<0.002) increase in risk of death independent of age, blood pressure, serum cholesterol, body mass index, and cigarette smoking habit; this effect remained (relative risk 1.46, P=0.05 adjusted for age and risk factors) after men with known diabetes, a HbA(1c) concentration >/=7%, or history of myocardial infarction or stroke were excluded. 18% of the population excess mortality risk associated with a HbA(1c) concentration >/=5% occurred in men with diabetes, but 82% occurred in men with concentrations of 5%-6.9% (the majority of the population).

CONCLUSIONS

Glycated haemoglobin concentration seems to explain most of the excess mortality risk of diabetes in men and to be a continuous risk factor through the whole population distribution. Preventive efforts need to consider not just those with established diabetes but whether it is possible to reduce the population distribution of HbA(1c) through behavioural means.