Testing for diabetes by measuring the HbA1c level rather than by glucose testing is more expensive and therefore unaffordable in many, if not most, parts of the world. However, this consideration may not be as significant when viewed from a societal perspective. At present, the asymptomatic person undergoing diagnostic testing requires two morning fasting tests to confirm a diagnosis of diabetes. A substantial proportion will require an OGTT. For many, this results in losing one to three working hours twice before a diagnosis is made. For HbA1c, the test can be performed outside normal working hours, and the increased costs of HbA1c may be more than balanced by the decreased costs carried by the patient. Furthermore, if HbA1c is introduced as a diagnostic test, market forces and competition should lead to a reduction in the costs of an HbA1c test. Projected costs and effectiveness could easily be modelled to examine the economic impact under differing scenarios.
Accuracy in measurement and standardisation of assays remains a concern with regard to HbA1c measurement. Although the IFCC together with EASD and ADA have developed a ‘reference anchor’ and thereby provided the possibility for international standardisation of the HbA1c measurement , this has not been fully implemented at present, but an updated examination of the laboratory measurements of glucose and HbA1c by the current International Expert Committee indicates that with advances in instrumentation and standardisation, the accuracy and precision of HbA1c assays at least match those of glucose assays.
The HbA1c test is not available in many parts of the world. This is primarily a problem in low- and middle-income countries, and is definitely a major concern. Introduction of HbA1c as the diagnostic test in this situation is not possible. These countries must have the option (as recommended in the report of the International Expert Committee ) of continuing with the current diagnostic criteria until the alternative becomes accessible and affordable.
Testing for diabetes by measuring HbA1c is not possible in all patients with abnormal haemoglobin traits, such as HbS, HbC, HbF and HbE, as they interfere with some HbA1c assay methods . Many assay methods can correct for the presence of the most common haemoglobin traits (see www.NGSP.org, accessed 8 August 2009). Alternatively, affinity assays that are unaffected by haemoglobin traits may be used . However, where HbA1c testing is limited or not currently available, the use of different routine methodologies to deal with these situations will not be practical in the short term.
Conditions that change erythrocyte turnover, such as haemolytic anaemia, chronic malaria, major blood loss or blood transfusions will lead to spurious HbA1c results. As for settings where HbA1c assays are unavailable, the traditional glucose-based diagnostic tests must be used in individuals for whom interpreting the HbA1c level is problematic.