Lot variation and inter-device differences contribute to poor analytical performance of the DCA Vantage™ HbA1c POCT instrument in a true clinical setting

Abstract

Objectives: The glycated haemoglobin fraction A_1c (HbA_1c) is widely used in the management of diabetes mellitus, and the Siemens DCA Vantage™ point-of-care testing (POCT) instrument offers rapid HbA_1c results even far from a clinical laboratory. However, the analytical performance has been questioned, and not much is known about effects of changing reagent lot, instrument and operator. We therefore compared the analytical performance of the DCA Vantage™ with established routine methods (Tosoh G8/G11 ion exchange HPLC) in a true clinical setting at two Danish hospitals.

Methods: We extracted all routine clinical HbA_1c results incidentally drawn from the same patient within 48 h (n=960 pairs) and evaluated the effect of reagent lot, operator and instrument. We also performed a prospective method comparison in our diabetes out-patient clinic (n=97).

Results: The critical difference (CD) between two POCT results varied between 5.14 and 6.61 mmol/mol (0.47-0.55%), and the analytical imprecision of the DCA Vantage™ (CV_A) was >3%. Significant effect of reagent lot and inter-instrument differences were found, whereas no effect of operator was seen.

Conclusions: The DCA Vantage™ HbA_1c analysis does not fulfil the prevailing analytical performance specifications, but rigorous validation of new reagent lots and continuous recalibration of instruments may potentially improve the precision substantially. Our findings, therefore, clearly emphasise the necessity of a close collaboration between clinicians and laboratory professionals in the POCT field. Finally, POCT HbA_1c results should always be interpreted together with other measures of glycaemic control to avoid inappropriate change of patient treatments due to measurement uncertainty.

Keywords: clinical laboratory techniques; glycated haemoglobin A; point-of-care testing.