Calibration and calibration verification are two distinct processes. The frequency and testing method vary for each of these processes. The frequency is determined as per the manufacturer's requirements and defined by compliance and accreditation organizations.
Clinical Laboratory Standards Institute (CLSI) defines calibration as a test process utilizing samples with a known range of analytes that involves testing and making adjustments to an instrument or the test system readout to correlate the measurement response and concentration of a substance (analyte) measured. The adjustments, if necessary, set the instrument to provide an accurate result for each of the tested analytes.
Calibration verification is the process of assaying materials of known concentration in the manner that patients (unknowns) are measured over the analytic range of the instrument. This process verifies that the test system accurately measures samples over the analytical range. CLIA has published requirements for calibration verification of all automated analyzers. These regulations include using a minimum of three calibrators (calibration samples) spanning the analytic range at least every six months. If routine calibration of the analyte incorporates at least three calibrators, the CLIA regulations are met, and additional calibration verification with alternate materials is not necessary.
CLIA regulations include an exception to calibration verification for automated cell counters. Calibration verification requirements are met if the laboratory follows the manufacturer's instructions for instrument operation. At least two levels of quality control material are analyzed daily and compared to the known values of the test materials. Acceptable values for this daily testing substantiate the instrument's calibration throughout the reportable range for patient test results.
A new calibration is required if, after following appropriate troubleshooting steps, the quality control results:
- Are out of acceptable range
- Produce unacceptable results that do not correct with repeat testing
- Show sudden shift or trend over a period of time
