Calibration Verification/Linearity and its Role in the Ever Expanding POCT Market

‘Is calibration verification/linearity required on my POCT system or not?’

If you are one of the many who have purchased an instrument for point of care testing (POCT) this is a very legitimate question.  POCT user manuals will typically state in one form or another that the linearity of the instrument should be checked before the instrument is used for patients for the first time.  The user manual may also refer to calibration verification in lieu of linearity, or it may refer to both terms.  And in many instances, but not all, the manufacturer may include a calibration verification/linearity kit with the initial shipment of the test system to be used upon initial set-up.   The user manual will also generally state that subsequent linearity tests are to be determined by the facility operating the system.  Which brings us to the question above.  Once the test system is calibrated, controls are set and ran, and calibration has been verified and/or linearity has been established, ‘Is calibration verification/linearity required on my POC test system moving forward?  And what exactly is the difference between calibration verification and linearity?’

Let’s tackle the last question first.  What is the difference between calibration verification and linearity?

Calibration verification is the process of assaying materials of known concentration in the same manner as patient samples to assure the test system is accurately measuring samples throughout the reportable range of the instrument.  Reportable range being the range of the test results for an analyte, from minimum to maximum, which the instrument test system can accurately measure.  Per CLIA guidelines at least three samples (low, middle & high) spanning the reportable range of the test are run as unknowns (performed in normal test mode, not calibration mode) and the values obtained are compared to the known values of the calibration verification material.  If the calibration verification confirms that calibration settings are valid for a specified method, no further calibration actions are necessary.  Calibration verification is to be performed every six months, or sooner if specified in the user’s test system instructions, the facility’s QC protocol and under circumstances outlined in CLIA 493.1255(b)(3).

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