Within-clinic glycosylated haemoglobin measurement

Comparison between a rapid glycohaemoglobin (HbA1c) immunoassay and other indices of glycaemic control

The aims of the study were to compare glycohaemoglobin (HbA1c) values measured by DCA (a benchtop analyzer primarily designed for within-clinic rapid HbA1c determination) to a reference HbA1c method and home blood glucose monitoring, and to explore the possibility of an uniform expression of data. A total of 103 blood samples and the corresponding mean capillary glucose values (4.4 +/- 1.2 tests/day) of the preceding 2 months were collected from 34 insulin-dependent diabetic adults. We measured the correlations and agreements using the residual plots method and regression equations between HbA1c measured by DCA and high-pressure liquid chromatography (HPLC), and between DCA and capillary glucose values. A highly significant correlation (r2 = 0.85, P < 0.001) and an acceptable agreement (97% of values within 2 SD of the mean difference of 0.9% +/- 0.4%) was found between DCA and HPLC values. The regression equation calculated on the first half of the cases was: DCA (%) = 0.72 HPLC (%) +1.38. Of DCA values expressed in HPLC terms using this equation 87% fell within a clinically acceptable confidence interval when compared with measured HPLC data. A significant correlation (r2 = 0.40, P < 0.01) was found between DCA and capillary glucose values, and the regression equation was: DCA (%) = 0.34 capillary glucose (mM) +4.44. Of glycaemic levels calculated from DCA values using this formula 82% fell within a clinically acceptable error range when compared with measured glycaemic values. We conclude that the three methods of assessment of diabetes control are well correlated and that it is possible, with a degree of precision acceptable for the clinical setting, to express all data in uniform units, e.g. mM of capillary glucose or percentage of HPLC-HbA1c, though a simple correspondence table based on our transfer equations may be clinically sufficient and more handy.

Evaluation of glycaemic control limits using the Ames DCA 2000 HbA1c analyser

The Ames DCA 2000 is a benchtop analyser that measures HbA1c by an agglutination inhibition immunoassay using a monoclonal antibody. Laboratory and nursing staff measured HbA1c on-site in 78 patients with Type 1 diabetes at the outpatient clinic. Significant correlations were noted with both the Corning Glytrac total HbA1 assay (r = 0.89) and the Novoclone assay for HbA1c (r = 0.95). Mean within-assay CV was 1.6% and 3.0% at HbA1c of 5.4% and 13.0%, respectively, while between-assay CVs were 4.2% and 3.8%. These results are as good as our routine laboratory method based on the Corning HbA1 assay. Locally derived reference population data for HbA1c were produced and patients were assigned to categories of good, acceptable, and poor glycaemic control using conventional recommendations for Type 2 diabetes. There was poor agreement between the methods, with only 22% of patients achieving good/acceptable control using the DCA 2000, while 46% of patients had an HbA1 in this range. It appears that the convention for derivation of control limits for HbA1 does not hold for this HbA1c assay.

A novel device for the rapid in-clinic measurement of haemoglobin A1c

In order to evaluate a novel technique for measuring haemoglobin A1c using a cassette-based immunoassay method we have undertaken a laboratory evaluation using 48 patient samples and a separate within-clinic prospective study of 59 diabetic patients. Individuals were recruited from general (48 patients), paediatric (19 patients), obstetric (24 patients), and general practice (15 patients) diabetic clinics. Agreement was evaluated between HbA1c results obtained using the new method (AMES DCA 2000) and an established laboratory assay (DIAMAT HPLC system). The mean differences between the two results (AMES DCA 2000-DIAMAT) (95% confidence intervals) were: laboratory -0.69% (-1.42 to 0.04%); paediatric clinic -0.93% (-1.93 to 0.07%); obstetric clinic -0.29% (-1.09 to 0.51%), and general practice clinic -0.77% (-1.3 to -0.24%). For the AMES DCA 2000, the coefficient of variation for HbA1c of 5.2% was 1.6% and for HbA1c of 13%, 2.4%. This instrument was used without difficulty by four different operators. Intra-assay coefficient of variation for each operator was < 3.4%. In 9/18 patients where a specific assessment of clinical utility was made, knowledge of the HbA1c result at the time of consultation lead to a change in treatment. Methodology of this type may be used successfully within a diabetic clinic setting in both primary care and hospital environments.

Can general practitioners assess diabetic control? Can anybody do any better?

A prospective study assessing the ability of various health professionals to estimate the control of diabetic patients from the accepted measures made for diabetes care was carried out. Patients were stratified into four categories according to the estimated HbA1c, and 45-60% were accurately assigned by the professionals. Patients were also divided into two broader groups according to their need to have changes in treatment made. None of the professionals could assign patients with Type 1 diabetes into these two groups with an accuracy of greater than 71%. With Type 2 diabetic patients accuracy improved up to 98% and there was little difference between the professionals. The current HbA1c was accurately predicted into two broad groups by the previous HbA1c alone in 89% of cases of Type 2 diabetes. These findings have implications for the routine care of diabetic patients and the education of health care professionals.