Monitoring long-term analytical quality by computerized combined Shewart-cusum method.

A computerized system for monitoring the long-term analytical quality has been developed. Input to the system is the control result obtained from a single analysis of a control specimen each day a test is run. To ensure comparability with random patient's specimens, lyophilized sera are reconstituted with variable (and secret) volumes of water for most tests included in the monitoring system. The control results are evaluated by a combined application of the Shewart control rule (limits at +/- 2 SD and +/- 3 SD) and decision limit cusum control, sensitive to imprecision and inaccuracy, respectively. Four years experience with the system is presented.