Quality-control scheme for blood glucose measured outside the laboratory.

We propose a quality-control (QC) scheme to evaluate the performance of blood glucose estimates made with a reflectometer in hospital wards or at home. We constructed a chart illustrating the comparison by regression analysis of the results of 254 reflectometer readings (y) and simultaneous capillary blood glucose analyses in the laboratory (x). Arbitrary acceptance limits around the regression line (y = 0.5 + 0.87x; r = 0.97, Sy/x = 0.8 mmol/L) were established, based on the mean +/- 2 SD of the reflectometer readings of a series of classes of 1.1 mmol/L interval, made with the results from the laboratory analyzer. Each ward using a reflectometer is provided with the QC chart, and the first blood glucose estimation with the reflectometer on each working shift is controlled by re-assay in the laboratory. If the reflectometer reading is outside the limits, the next glucose estimation is also re-assayed. If two consecutive readings are outside the limits, the reflectometer procedure is considered to be failing, the instrument's readings are not used for medical decisions, and remedial action is taken. The chart can also be used as a teaching tool for training the patients or the nurses and to evaluate individual performance.