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Abstract
IntroductionLiquid chromatography coupled to atmospheric pressure ionization tandem mass spectrometry (LC-ESI-MS/MS) is currently considered the reference method for quantitative determination of urinary free cortisol (UFC). One of the major drawbacks of this measurement is a particular form of matrix effect, conventionally known as ion suppression.Materials and methodsWe describe here the case of a 66-year-old-patient referred to the daily service of general medicine for intravenous antibiotic administration due to a generalized Staphylococcus aureus infection and for routine 24 hours UFC monitoring in the setting of glucocorticoid replacement therapy.ResultsThe observation of 10-fold decrease of internal standard of cortisol signal led us to hypothesize the presence of an ion suppression effect due to a co-eluting endogenous compound. Screening analysis of tandem mass spectrometry (MS/MS) spectra of the interfering molecule, along with in vitro confirmation analyses, were suggestive of the presence of high concentration of piperacillin. The problem was then easily solved with minor modifications of the chromatographic technique.ConclusionsAccording to our findings, antibiotic therapy with piperacillin/tazobactam should be regarded as an important interference in UFC assessment, which may potentially affect detection capability, precision and accuracy of this measurement. This case report emphasizes that accurate anamnesis and standardization of all phases of urine collection are essential aspects for preventing potential interference in laboratory testing.
Highlights
Liquid chromatography coupled to atmospheric pressure ionization tandem mass spectrometry (LC-electrospray ionization (ESI)-MS/MS) is currently considered the reference method for quantitative determination of urinary free cortisol (UFC)
Due to its higher selectivity and specificity compared to conventional immunoassays, liquid chromatography - tandem mass spectrometry (LC-MS/MS) has become the reference technique for measuring UFC in clinical practice
MS detection is not completely foolproof, especially when coupled with electrospray ionization (ESI) sources, the most widely used interfaces used for UFC assessment
Summary
We describe here the case of a 66-year-old-patient referred to the daily service of general medicine for intravenous antibiotic administration due to a generalized Staphylococcus aureus infection and for routine 24 hours UFC monitoring in the setting of glucocorticoid replacement therapy
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