Point-of-care testing of HbA1C is traceable to IFCC reference method by external calibration.

BACKGROUND

POCT for HbA1C is widely used in China. However, the lack of traceability of POCT leads to poor comparability of patient results.

METHODS

The first step was the evaluation of the precision of NycoCard and DCA by using two-level patient specimens. The second step was the calibration of the central laboratory instrument G8 HBA1C Variant with samples whose values had been assigned by an IFCC reference method. The third step was the assignment of values to 50 fresh whole blood patient specimens by this calibrated G8. The fourth step was to use these 50 fresh whole blood patient specimens to calibrate and to revise the POCT instruments. The fifth step was to confirm whether these 50 specimens were required through mathematical calculations.

RESULTS

The low and high CVs at levels were 3.61% and 1.85% for NycoCard but 1.71% and 2.85% for DCA. The linear equation of NycoCard to calibrated G8 and that of DCA to calibrated G8 were Y=0.8530X+0.6409 and Y=0.8995X+0.3891, respectively, and the correlation coefficient for every POCT instrument was greater than 0.985. By external calibration of POCT instruments, the mean deviation detected by NycoCard was reduced from -4.0±3.4mmol/mol to 0.5±3.9mmol/mol, and that by DCA went down to 0.2±3.3mmol/mol. The minimum specimen size for the external calibration of POCT instrument was 10.

CONCLUSION

POCT measurement traceability can be established by external calibration. Using an external calibration mode improves the comparability of POCT patient results.