A. Larbig, P. Kaiser, U. Kramer, I. Schellenberg, M. Spannagl
Background
No suitable control material is currently available for external quality assurance of point-of-care testing (POCT) for glucose. Since both the analyte, glucose, and the matrix, whole blood, are unstable without additives, current interlaboratory tests are based on glucose measurement in blood plasma. However, POCT devices are generally designed for glucose measurement in capillary blood. INSTAND e.V. has therefore recently presented a new concept for a control material in glucose POCT: the Whole Blood Beads model (WBB).
Methods
The WBB model is based on two components: a glucose polymer bead containing a defined amount of glucose and a glucose-free whole blood matrix. The bead is dissolved in the whole-blood matrix immediately before measurement.
Its suitability as a control material was evaluated based on the results of interlaboratory test 807 2024-T4. The target value was determined using a reference method (GC-IDMS) and serves as an evaluation criterion for the WBB model's accuracy. Any limitations of the WBB model were identified based on the interlaboratory test results and the participants' experiences.
Results
The EQA scheme results show a pass rate of 66.2% with a high degree of accuracy (approx. -2% bias), although there is room for improvement in precision (coefficient of variation of approx. 13%).
Based on the experiences of the EQAS participants, the low precision was associated with insufficient mixing of the glucose beads and the whole blood matrix. Therefore, new tubes with lower dead volume and transparent labels will be introduced for future interlaboratory tests. In addition, difficulties with sample handling were noted, which will be addressed with detailed instructions for conducting the interlaboratory test.
Conclusion
The WBB model performs well in terms of accuracy in the 807 2024-T4 proficiency testing program and offers a promising option for whole blood-based accuracy control in glucose POCT analyses. The continuous optimization of the WBB model for sample handling aims to improve the currently low precision, enable participant-friendly application in EQA schemes, and thus ensure the accuracy and reliability of POCT glucose measurements for patient care.
