The analytical goals for hemoglobin A(1c) measurement in IFCC units and National Glycohemoglobin Standardization Program Units are different

HbA1c: a review of analytical and clinical aspects

After the relationship between glycemic control and the HbA1c concentration was demonstrated, many tests have been developed to determine the HbA1c concentration. The test results are standardized to the International Federation of Clinical Chemistry (IFCC) Reference Measurement Procedure (RMP) in harmony with the efforts of the National Glycohemoglobin Standardization Program (NGSP). The longitudinal use of the test requires strict quality management including accreditation of the laboratory, a dedicated internal control design, participation in an external quality assessment (EQA) program (proficiency test), and careful consideration of pre- and post-analytical aspects of the test. Performance goals for optimizing determination of the HbA1c concentration have been described. As an index of long-term glycemic control and a risk predictor, the HbA1c concentration is an indispensable part of routine management of diabetes. Because of the improving quality of the test, the HbA1c concentration is being increasingly applied in the diagnosis of diabetes. There are, however, concerns of this application in point-of-care settings. The HbA1c concentration is also used to achieve stringent control in pregnant diabetic patients. Strict standardization enables the definition of universal reference values and clinical decision limits. This review describes the present status of analytical and clinical aspects of determining the HbA1c concentration and highlights the challenges involved.

Multicenter evaluation of hemoglobin A1c assay on capillary electrophoresis

BACKGROUND

Hemoglobin A1c (HbA1c) measurement is currently used for the routine monitoring of long-term glycemic status, thus playing a fundamental role in the management of this disease. Since this marker has recently been recommended as an additional tool for diagnosing diabetes, it's of the utmost importance to ensure that the precision and accuracy of HbA1c methods are satisfactory.

METHODS

We assessed the analytical performances of the Capillarys 2 Flex Piercing® analyzer and compared the results obtained with those from two other widely used HPLC instruments. Furthermore, we evaluated the convenience and ergonomics of the system in authentic routine work conditions in three centers.

RESULTS

Within-laboratory (n=40) and between-laboratory (n=120) imprecision CV% using four blood samples with different concentrations of HbA1c were <3.4% and <3.1% using IFCC units and <2.1% and <2.0% using NGSP units, respectively. The obtained trueness (<3 mmol/mol, <0.3%) was highly satisfactory, nor was HbA1c measurement compromised by the presence of the commonly present hemoglobinopathies. The comparison made with established methods revealed excellent agreement (r>0.985).

CONCLUSIONS

The evaluated method is precise, accurate and robust, with a high throughput. It also allows the identification of the most frequent Hb variants and therefore may be a valid alternative to other methods currently proposed for routine use in clinical laboratories.

Use of HbA1c in the diagnosis of diabetes mellitus in the UK. The implementation of World Health Organization guidance 2011

The WHO was very clear that an HbA(1c) of 48 mmol/mol (6.5%) and above is diagnostic of diabetes. They were less clear regarding results that fell below 48 mmol/mol. The WHO recognize that individuals with HbA(1c) values below the cut-off point may still have diabetes, but give no guidance on how to investigate further. It is important that these individuals, who may be at increased risk of developing diabetes, are monitored correctly; a recommended scheme is given in Fig. 2; following these recommendations will ensure at-risk people are not overlooked and will be monitored closely. Even although it is not recommended to combine HbA(1c) with glucose measurement for diagnosis, the WHO did not discount the value of a fasting glucose and an oral glucose tolerance test to diagnose diabetes in selected individuals; it is the responsibility of the investigating doctor to choose how best to diagnose on an individual basis. This new method of diagnosing diabetes will identify a different cohort as having diabetes than is currently being diagnosed; but the process of investigation that does not require a fasting sample makes investigation easier, allowing more people to be investigated.

Controversies on how diabetes is diagnosed

PURPOSE OF REVIEW

To evaluate the controversial aspects of diabetes diagnosis.

RECENT FINDINGS

Within the past 2 years, revised guidelines for the diagnosis of diabetes have been issued which endorse the use of the hemoglobin A1C as a diagnostic test, in addition to the previously recommended tests. Updated diagnostic criteria for gestational diabetes were also published in the same period. Recent publications on the current role of oral glucose tolerance tests and diagnosis of diabetes in the acutely ill are sparse. There are new recommendations regarding the use of genetic testing and antibody testing in establishing the cause of diabetes.

SUMMARY

The inclusion of A1C as a diagnostic test has many advantages including reproducibility of the test and convenience, but there are situations where the test is unreliable and it misses many individuals who would have been diagnosed by plasma glucose testing. The diagnostic threshold of 6.5% for the A1C remains controversial. There is still no consensus on the best approach to diagnose gestational diabetes. The role of the oral glucose tolerance test seems to be diminishing. Diagnosis of diabetes in acute illness is aided by A1C testing. Genetic and autoantibody testing in specific situations offer diagnostic and therapeutic utility.