I run a POCT cardiac panel with fairly large CVs. Can I set tighter QC limits on it?

I run a POCT cardiac panel with fairly large CVs. Can I set tighter QC limits on it?

Remember that coefficient of variation (CV) reflects the imprecision or random error of a method. When the method’s error distribution is symmetrical or bell-shaped gaussian, 68% of the observed QC values for a particular control fall within + 1 SD, 95% for + 2 SD, and 99.7% for + 3 SD. This means that depending on the SD rule selected to evaluate the QC results, by definition 32% of QC values will fall outside + 1 SD, 5% outside of  + 2 SD, and 0.3% or 3 values in 1,000 when + 3 SD limits are used. All QC regulations mandate that test sites respond to situations where QC value(s) fall outside established limits. Yet depending on the QC rule(s) used, many of the results outside these limits will be false alarms – signaling a problem when none exists.

By setting “tighter” limits, more QC values will fall outside that limit and each out-of-control result requires investigation.  In reality, when a test site determines the CVs are too large for a methodology to deliver medical useful information, another (accurate) method with less random error should be selected and then the right QC rule(s) applied based on quality goals and method performance to minimize false rejection.

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