ABSTRACT
BACKGROUND: 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.
Subject(s)
Chromatography, High Pressure Liquid/methods , Hydrocortisone/urine , Tandem Mass Spectrometry/methods , Adolescent , Adult , Aged , Cushing Syndrome/diagnosis , Data Accuracy , Female , Humans , Male , Middle Aged , Young AdultABSTRACT
Circulating vitamin D is found in various forms: 25-hydroxyvitamin D or calcidiol, majority circulating form, is a "pro-hormon" which will be converted to 1,25-dihydroxyvitamin D or calcitriol, hormone corresponding to vitamin D active form. While determination of 25-hydroxyvitamin D serum levels reflects vitamin D status of patients, determination of 1,25-dihydroxyvitamin D serum level is only indicated in rare cases of suspected hypersensitivity vitamin D in children or of sarcoidosis in adults. There are too many confusion between these two vitamin forms, resulting in inappropriate prescription of 1,25-dihydroxyvitamin D. Here, we describe a case of hypersensitivity to vitamin D by mutation of CYP24A1. We propose to review the interest of 1,25-dihydroxyvitamin D assay in different pathologies, to describe the assay techniques and remind the good prescribing practices of this parameter.
