Comparison of performance of classical clinical chemistry analysers with test-strip devices (Reflotron) and those based on film technology (Vitros) in external quality assessment (EQA) surveys.

This article reports on the performance of two "dry" chemistry devices, (Reflotron, Roche Diagnostics and Vitros, Johnson & Johnson) and compared them with classical "wet" chemistry analysers in four commercially produced quality assessment samples (Roche PNU and PPU and Seronorm Human and Human High Controls) sent repeatedly over a 12-month observation period. Eleven analytes (including five enzymes) were studied, eight of which had target values set by reference method procedures. The results showed that both devices gave comparative results for the same sample sent in different EQA-surveys. Statistically significant differences which occurred were due to the high precision of measurement with a minimal shift in the measured concentrations. They had no clinical relevance in interpretation of results. Comparisons between "dry" and "wet" chemistry results for the same analyte were almost always statistically significantly different and often large enough to influence the clinical interpretation of results. Examples here were glucose and uric acid measured with the Reflotron and compared with other Roche devices (Cobas, Hitachi). The Vitros showed deviant values for urea and creatinine, when compared with other measuring devices using liquid reagents. Differences seen were constant over time, but must be seen in context with the matrices of the samples sent. The results show the long term stability of both reagents and test kits, a necessary prerequisite for long-term controlling of precision and indirectly accuracy of patient measurements.