Abstract
BackgroundAn open problem in clinical chemistry is the estimation of the optimal sampling time intervals for the application of statistical quality control (QC) procedures that are based on the measurement of control materials. This is a probabilistic risk assessment problem that requires reliability analysis of the analytical system, and the estimation of the risk caused by the measurement error.Methodology/Principal FindingsAssuming that the states of the analytical system are the reliability state, the maintenance state, the critical-failure modes and their combinations, we can define risk functions based on the mean time of the states, their measurement error and the medically acceptable measurement error. Consequently, a residual risk measure rr can be defined for each sampling time interval. The rr depends on the state probability vectors of the analytical system, the state transition probability matrices before and after each application of the QC procedure and the state mean time matrices. As optimal sampling time intervals can be defined those minimizing a QC related cost measure while the rr is acceptable. I developed an algorithm that estimates the rr for any QC sampling time interval of a QC procedure applied to analytical systems with an arbitrary number of critical-failure modes, assuming any failure time and measurement error probability density function for each mode. Furthermore, given the acceptable rr, it can estimate the optimal QC sampling time intervals.Conclusions/SignificanceIt is possible to rationally estimate the optimal QC sampling time intervals of an analytical system to sustain an acceptable residual risk with the minimum QC related cost. For the optimization the reliability analysis of the analytical system and the risk analysis of the measurement error are needed.
Highlights
In clinical chemistry the minimal required frequency of statistical quality control (QC) applied to analytical systems has been the testing of at least one control sample per level of concentration of the measurand, at two levels of concentration, once per 24 hr
On the other hand less frequent QC is required if the system includes an internal monitoring system, as this system detects the potential critical failures, except if it fails too
The equivalent QC concept has initiated a debate about the optimal QC frequency
Summary
In clinical chemistry the minimal required frequency of statistical QC applied to analytical systems has been the testing of at least one control sample per level of concentration of the measurand, at two levels of concentration, once per 24 hr. An open problem in clinical chemistry is the estimation of the optimal sampling time intervals for the application of statistical quality control (QC) procedures that are based on the measurement of control materials. This is a probabilistic risk assessment problem that requires reliability analysis of the analytical system, and the estimation of the risk caused by the measurement error
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