The HbA1c blood test is the accepted standard for monitoring long-term glycemic control in patients with diabetes, however until recently, HbA1c was not recommended for diagnosing or screening for diabetes.

In a retrospective study carried out by DynaLIFEDx, Edmonton, AB, Canada) in conjunction with local medical practitioners, evaluated the positive predictive value (PPV) and negative predictive value (NPV) of HbA1c against the oral glucose tolerance test (OGTT) values using a 10% prevalence of diabetes in three locations. DynaLIFEDx is a major Canadian medical laboratory offering a complete range of diagnostic testing services. For a three-year period, 3,163 data pairs were collected including 1,537 males and 1,626 females with a mean age of 55.4 ± 14.7 years. The OGTT criteria for diabetes were found for 568 out of the 3,163 sets.

Blood glucose was measured on the ARCHITECT ci8200 (Abbott Laboratories; Mississauga, ON, Canada) using a hexokinase method and HbA1c was measured by high performance liquid chromatography (HPLC) on a VARIANT II analyzer (Bio-Rad laboratories, Montreal, QC, Canada). The recommended threshold HbA1c value of 6.5% did not give the optimal combination of NPV of 0.93 to 0.92 and PPV of 0.40 to 0.61 compared to a threshold HbA1c value of 7.0% that gave an NPV of 0.91 to 0.92, and PPV of 0.61 to 0.73.

The authors concluded that HbA1c is not satisfactory for use as a diagnostic test for diabetes using the threshold values recommended by the Consensus Committee and the International Expert panel due to low positive predictive values. About 12% of individuals with a normal OGTT test will be diagnosed with diabetes using a threshold HbA1c value of 7.0%. This would put considerable burden on health care resources. However, based on the high negative predictive value, HbA1c may be used as a test to rule-out diabetes. The study was published in the December 2011 issue of the journal Clinical Biochemistry.

Related Links:
DynaLIFEDx
Abbott Laboratories
Bio-Rad