Given questions about these tests’ utility, lab professionals urge caution in implementing them and identify key steps in validating them to achieve as robust results and interpretation as possible.

One lab has had a LC-MS/MS serum gabapentin quantification assay since 2015, but recently the calibration curve became quadratic instead of linear. What could have caused this? One respondent suggests several potential reasons, from an aging detector to an inadvertent change in the curve weighting setting that could make a curve appear to fit better with a quadratic rather than a linear equation. To try to pinpoint the cause, he suggests comparing the gabapentin and ISTD raw signal areas before and after the problem started.

A number of factors contribute to wide variability in cortisol measurements across platforms. Thus, establishing an appropriate serum cortisol cut-off for each assay is critical to supporting clinical decision-making and preventing misdiagnosis.