AbstractBackground:Twenty-four hour urinary free cortisol (UFC) determination can be used for screening and follow-up of Cushing syndrome (CS). As immunoassay methods lack specificity for UFC measurement, the use of high-performance liquid chromatography coupled to mass spectrometer (LC-MSMS) is recommended. The aim of our study was to compare UFC results using four LC-MSMS methods performed in four independent laboratories in order to evaluate interlaboratory agreement.Methods:Frozen aliquots of 24-h urine samples (78 healthy volunteers and 20 patients with CS) were sent to four different laboratories for analysis. Following liquid-liquid or solid-liquid extraction, UFC were determined using four different LC-MSMS assay.Results:UFC intra- and interassays variation coefficients were lower than 10% for each centre. External quality control results were not significantly different. UFC normal ranges (established from healthy volunteers) were 17–126, 15–134, 12–118 and 27–157 nmol/day, respectively. Classification of UFC from healthy volunteers and patients with CS using a 95th percentile threshold was similar. However, for extreme UFC values (<50 or >270 nmol/day), negative or positive bias was noted.Conclusions:Even for highly specific methods such as LC-MSMS, variations of results can be found depending on analytical process. Validation of LC-MSMS methods including determination of the reference range is essential.
Clinical Chemistry and Laboratory Medicine (CCLM) – de Gruyter
Published: Jun 27, 2018
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