Introduction of new calibrator lots for quantitative protein mass spectrometry and adjustment of calibration settings...

Calibration is a cornerstone of clinical chemistry test results and maintaining an in-house LDT requires periodic renewal of calibrators. Here we present the introduction of a new set of native human serum calibrators, using different curve fitting approaches for long-term quantitation of nine apolipoproteins with traceability to current metrological traceability chains.

Five "old" native human serum calibrators (OC), have been used successfully for >6 years for quantitation of apolipoproteins by LC-MS. Five new calibrators (NC) were selected and value assigned by standard operating procedures. Calibration with OC used linear regression without constraining the intercept. In addition, regressions including the origin as a datapoint and forcing the origin were evaluated, and NC were recalculated using the OC under origin-forced conditions.

The new calibrator set showed higher concentration ranges for all apos, except apoC-III. Including the origin as a datapoint in the linear regression improved stability of calibration lines (with reduction of slope variation and intercepts). Recalculation of the NCs and their subsequent application with origin forced, omitted intercepts of linear regression and in general reduced slope variations (<11.8 %CV, for all apos, except apo(a) with imprecision <9.1 % for all apos for two QC samples.

In a complex system like the mass spectrometric quantitation of multiple proteins, calibration with linear regression using origin forced appears to be a well-suited approach offering guaranteed long-term consistent quality and clinical use of the apolipoprotein test.