6.1.1.1 Discrepancy in HbA1c Measurements Performed at Different Local Laboratories and at a Selected Central Reference Laboratory

Abstract

As participants in a general practice intervention study, 66 patients had their HbA_1cmeasured both at a local and at a selected central reference laboratory. A discrepancy in the results was observed, as 97% of the results measured locally were lower than the centrally determined results. Bias (as calculated from mean value of measured HbA_1c) between local laboratories and the central laboratory was measured to - 1.47 % HbA_1c. A bias of this magnitude gave “problems” both to the general practitioners, patients and laboratories.

To reduce the “problems” a bias of 0.5% HbA_1c is estimated to be acceptable. But, to avoid these “problems” totally, a bias of 0.25% HbA_1c is estimated to be the highest allowed bias. For HbA_1c, a control system for both control of method standardisation and for specificity is described.