Glycated haemoglobin assays. Approaches to standardization of results

Best use of the recommended IFCC reference method, material and values in HbA1Canalyses

The results of Finnish HbA(1C) surveys (Labquality Ltd.) during the past 10 years have undergone continuous improvement with smaller overall coefficients of variation for the HbA(1C) mean values of all methods (from 7.5 to 5.4% for normal and from 8.9 to 4.7% for diabetic samples). Most of the HbA(1C) methods are certified for traceability to the Diabetes Control and Complication Trial (DCCT) designated comparison method, which originally was a high-performance liquid chromatography (HPLC) method (Bio-Rex 70, Bio-Rad) but is no longer in routine use. It was therefore important that the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) had prepared both reference preparations and method for the determination of HbA(1C). However, the very demanding reference method is not realistic for use in clinical laboratories. According to the present study, the mean HbA(1C) values of the Labquality Ltd. showed significant correlations to the HbA(1C) values of The European Reference Laboratory for Glycohemoglobin (r = 0.999) and to the values using the IFCC method (r = 0.999). The reference values of the IFCC method (mainly those of the manufacturer) range from 2.85 to 3.81%, being significantly lower than the present DCCT values (4.0-6.1%). Since it may take some time before consumers are ready to accept the new IFCC reference values for general use, we propose that the IFCC reference materials and method should be used for calibration of the present methods to the well-known DCCT levels.

Haemoglobin A1c analysis in the management of patients with diabetes: from chaos to harmony: Table 1

Effective management of patients with diabetes mellitus requires accurate assessments of blood glucose control. The best characterised marker of long term glycaemic control is whole blood haemoglobin A1c (HbA1c). Published clinical trials have identified quantitative and direct relationships between the HbA1c concentration and risks of diabetic microvascular complications. However, in order to practice evidence-based medicine, assays used to measure patient samples should ideally produce values comparable to the assays used in these trials. Numerous assays using chromatographic and immunological detection methods are used around the world. This paper briefly reviews the scientific evolution of HbA1c and its analysis, discusses the reasons why HbA1c assay standardisation is a challenge, describes the approaches that have been adopted to harmonise HbA1c assays, and addresses the current initiatives to standardise HbA1c globally. These efforts have established HbA1c as an essential component in the management of patients with diabetes mellitus and are likely to lead to the use of HbA1c in the screening/diagnosis of diabetes.

Does HbA1C predict isolated impaired fasting glycaemia in the oral glucose tolerance test in subjects with impaired fasting glycaemia?

Background

To assess the usefulness of erythrocyte glycated haemoglobin (HbA1C) as a screening tool to identify those subjects with impaired fasting glycaemia (IFG) who do not have impaired glucose tolerance (IGT) or diabetes mellitus (DM) on a 75 g oral glucose tolerance test (OGTT).

Design and methods

All subjects undergoing an OGTT had HbA1C measured at baseline. Receiver operator characteristics analysis was used to identify optimal HbA1C cut-off values for diagnosing and excluding IGT and DM.

Results

We studied 140 subjects (69 women) with IFG (fasting capillary plasma glucose between 6.1–6.9 mmol/L). Using World Health Organisation criteria, 27 had isolated IFG, 56 had IGT and 57 had DM. HbA1C was higher ( P < 0.001) in patients with DM (6.8 ± 0.93%) when compared with those with IGT (6.3 ± 0.68%) and isolated IFG (6.2 ± 0.30%), but HbA1C was similar in those with IGT and isolated IFG. There was no HbA1C cut-off value differentiating isolated IFG from IGT or DM. None of the subjects with isolated IFG had HbA1C concentration of >6.8%, but 76% and 54% subjects with IGT and DM, respectively, had HbA1C of ≤6.8%.

Conclusions

HbA1C measurement is of limited value in differentiating isolated IFG, IGT and DM in subjects with IFG. It cannot be used to identify which subjects with IFG do not require an OGTT.

HbA(1c) as a screening tool for detection of Type 2 diabetes: a systematic review

AIM

To assess the validity of glycated haemoglobin A(1c) (HbA(1c)) as a screening tool for early detection of Type 2 diabetes.

METHODS

Systematic review of primary cross-sectional studies of the accuracy of HbA(1c) for the detection of Type 2 diabetes using the oral glucose tolerance test as the reference standard and fasting plasma glucose as a comparison. RESULTS Nine studies met the inclusion criteria. At certain cut-off points, HbA(1c) has slightly lower sensitivity than fasting plasma glucose (FPG) in detecting diabetes, but slightly higher specificity. For HbA(1c) at a Diabetes Control and Complications Trial and UK Prospective Diabetes Study comparable cut-off point of > or = 6.1%, the sensitivity ranged from 78 to 81% and specificity 79 to 84%. For FPG at a cut-off point of > or = 6.1 mmol/l, the sensitivity ranged from 48 to 64% and specificity from 94 to 98%. Both HbA(1c) and FPG have low sensitivity for the detection of impaired glucose tolerance (around 50%). CONCLUSIONS HbA(1c) and FPG are equally effective screening tools for the detection of Type 2 diabetes. The HbA(1c) cut-off point of > 6.1% was the recommended optimum cut-off point for HbA(1c) in most reviewed studies; however, there is an argument for population-specific cut-off points as optimum cut-offs vary by ethnic group, age, gender and population prevalence of diabetes. Previous studies have demonstrated that HbA(1c) has less intra-individual variation and better predicts both micro- and macrovascular complications. Although the current cost of HbA(1c) is higher than FPG, the additional benefits in predicting costly preventable clinical complications may make this a cost-effective choice.

HbA1c: A comparison of NGSP with IFCC transformed values

BACKGROUND

An approved IFCC reference method for measuring HbA1c, with a firm and reproducible correlation with NGSP values, is now available. We established (i) the degree of agreement of HbA1c results between the NGSP-certified and the IFCC-calibrated (converted to NGSP values) immunochemical method and (ii) the difference in the classification of control of diabetes mellitus (DM) in individual patients between the methods.

METHODS

HbA1c was measured on the same hemolysate from each patient by both methods (n=92). Results were analyzed by the kappa statistic, linear regression, and McNemar's chi(2) test.

RESULTS

Both methods achieved acceptable analytical performance. The kappa statistic measure of agreement was 0.65 and r(2)=0.937. Overall, 21 (22.8%) patients were classified differently in the extent of diabetes control (good, acceptable, or poor), with a significant difference between the 2 methods (p<0.0005).

CONCLUSIONS

The IFCC converted to NGSP values were significantly different from the previously used NGSP-certified method. The differences between the 2 methods are of sufficient magnitude that HbA1c results from these methods are not interchangeable. The IFCC method being scientifically superior in concept and design should replace the NGSP method. New HbA1c targets for DM management need to be established for the IFCC method.

Unreliable estimation of HbA due to the presence of Camperdown haemoglobin [beta 104 (G6) Arg --> Ser]

AIMS

To suggest the possible unreliability of HbA(1c) determination in presence of haemoglobin variants during routine metabolic evaluation.

METHODS

We present a case of Camperdown haemoglobin, accidentally detected in a middle-aged Italian man during routine metabolic evaluation for newly diagnosed diabetes. The haemoglobin variant has been identified by exchange high performance liquid chromatography (CE-HPLC) (VARIANT trade mark HbA(1c) Program, Bio-Rad Laboratories, Hercules, CA, USA), and characterized at molecular level by direct sequencing.

RESULTS

A 56-year-old male of Northern Italian origin, presented to our centre for a Type 2 diabetes mellitus of recent diagnosis. HbA(1c) determination was routinely determinated. The patient's chromatogram showed an inappropriate peak of 38.5% in the HbA(1c) position suggestive for the presence of abnormal haemoglobin. Further evaluation identified an abnormal haemoglobin peak even higher (49.5%) eluting at 1.34 minutes in P2-window. Molecular characterization of the mutation showed a nucleotide replacement, AGG --> AGC at codon 104, causing the amino acid replacement Arg --> Ser at position 104 (G6) that give rise to Hb Camperdown.

CONCLUSIONS

Haemoglobinopathies can lead to inaccurate glycated haemoglobin level determination. In patients carrying haemoglobin variants, the different methods for determinations of glycated haemoglobin could result in different errors, showing either higher or lower values than expected.

Evaluation of HbA1C results in an external quality assessment scheme in South Africa

BACKGROUND

Measuring HbA1c blood levels allows us to assess average glycaemia in individuals during the preceding 6-8 weeks. There is a clear association between increasing risk of complications with higher HbA1c values and a significant risk reduction of the complications with lower HbA1c values.

METHODS

The performance of South African laboratories in an External Quality Assurance scheme for HbA1c is reported.

CONCLUSIONS

A number of laboratories and methods do not meet the required analytical standards. South African laboratories should adopt measures similar to other regional and national initiatives to significantly improve laboratory performance and bring about harmonization of HbA1c assays.

Silent haemoglobin variants and determination of HbA(1c) with the HPLC Bio-Rad Variant II

AIMS

To evaluate the determination of HbA(1c) with an automated high performance liquid chromatography (HPLC) method in patients with clinically silent haemoglobin variants.

METHODS

HbA(1c) values were determined with the ion exchange HPL Bio-Rad Variant II using the high resolution beta thalassaemia programme in patients with silent haemoglobin variants, namely: Hb Graz, Hb Sherwood Forest, Hb O Padova, and Hb D.

RESULTS

All of these haemoglobin variants caused additional peaks in the chromatograms. No clinically useful HbA(1c) results were produced for patients with Hb Graz and Hb Sherwood Forest, the results for the patient with Hb D were too low, but the results for patients with Hb O Padova were acceptable.

CONCLUSIONS

The development of this automated HPLC method modification with high resolution mode aids the identification of interference caused by the described clinically silent haemoglobin variants in HbA(1c) determination.

Considerations on blood glucose management in Type 2 diabetes mellitus

In recent years the benefits of more intensive management in preventing or delaying the development and progression of diabetic complications have been well documented. What is not as well documented is how to motivate the person with diabetes to manage the condition, how to set, assess and quantify glucose goals, and the glucose variables that should be routinely measured. This review discusses the importance of setting targets and communicating them in a way that the patient understands. When aiming for a glycaemia target, balance is required (1) between achieving reduction of complications and causing an increased degree of hypoglycaemia, and (2) between what is achievable and what degree of benefit is gained. Target values given in guidelines should be adapted by the clinician to take into account the patient's susceptibility to hypoglycaemia, stage and type of complications, age and life expectancy, co-morbidity, social environment, understanding of the steps required and level of commitment to the treatment. Several suggestions are given regarding possible improvements and amendments to existing guidelines for diabetes management in treating to glucose goal. For example, attention should be drawn to the need to individualize goals and to consider education, long-term support, patient needs and treatment outcome when formulating diabetes management plans. The relative properties of the different glucose variables-fasting plasma glucose (FPG), postprandial plasma glucose (PPG), glycated haemoglobin A(1c) (HbA(1c)), and glycated protein-in terms of their convenience of measurement, usefulness and relevance to the physician and patient are also evaluated. When prioritising the variables to be measured it is suggested that where feasible, HbA(1c) should be the standard measurement by which to gauge risk and treatment efficacy. Serial measurements should be made and, where possible, the use of blood glucose meters encouraged, in order to obtain a blood glucose profile for the patient.