How Much QC is Enough?
Laboratories perform a lot of instrument quality control. Hematology analyzers have at least three levels of QC performed on one or more sampling modes, patient controls, and built-in trending (X-bar cumulative averages). Urinalysis and coagulation analyzers have 2 levels of control. Chemistry uses the most commercial material with 2 or 3 levels of control for all methods; in our laboratory general chemistry is 2 while immunoassay and other special testing is 3.
We run all this testing almost without thinking and in many cases seeing. In may be done on off shifts to improve efficiency, depending on volume. Added to this is QC performed to troubleshoot instrument problems, ensure unusual results are accurate, check calibration accuracy, etc.
All this material not only chews up time and reagents, but space as well. Lots are sequestered annually and arrive monthly, quarterly, or periodically to be stored in limited refrigerator or freezer space. Often, there are multiple lots, since unassayed controls have to be run in tandem to perform crossover testing until peer data is established. And typically labs order more QC than necessary for those “just in case” troubleshooting incidents. We never know exactly how much will be needed, and it’s better to have too much than not enough.
But how much is enough?
CLIA requires (Subpart K, 493.1256) that two control materials of different concentrations be used to monitor testing that correlate with patient values. For example, an elevated bilirubin control might be run before testing a neonatal sample. A low level protein control can be used for non-serum samples, such as cerebrospinal fluid. These specialty controls are in addition to routine commercial controls.
The interpretive guidelines also state for hematology analyzers that “acceptable controls are 2 levels of assayed materials, OR 1 level of assayed material and 1 patient specimen that was verified in the same batch of specimens with the assayed control material.”
If a laboratory runs three or more levels of control is there an opportunity to reduce and streamline? I wonder. Have any of your labs cut back on commercial controls to save money?
NEXT: Questioning Physicians