• Paul Zajic, Stefan Heschl, Michael Schörghuber, Petra Srekl-Filzmaier, Tatjana Stojakovic, Viktoria Weixler, Sieglinde Zelzer, and Karin Amrein.
• Div. of General Anaesthesiology, Emergency- and Intensive Care Medicine, Dept. of Anaesthesiology and Intensive Care Medicine, Medical University of Graz, Graz, Austria. paul.zajic@medunigraz.at.
• Wien. Klin. Wochenschr. 2021 Feb 1; 133 (3-4): 79-85.

BackgroundThere is controversy about the impact of acute illness on vitamin D levels. This study was carried out to assess the influence of perioperative fluid loading on 25-hydroxy-vitamin D [25(OH)D] levels. The study evaluated the clinical utility of a commonly available chemiluminescence assay (ECLIA, IDS-iSYS) and liquid chromatography/mass spectrometry (LC-MS/MS) in the diagnosis of vitamin D deficiency in this setting.MethodsIn this prospective observational pilot study in adult patients undergoing cardiovascular surgery on cardiopulmonary bypass (CPB), blood samples drawn at preoperative baseline (t1), after weaning from CPB (t2), on intensive care unit (ICU) admission (t3) and on the first (t4) and second (t5) postoperative days were analyzed.ResultsA total of 26 patients (130 samples) were included in this study. Fluid loading by CPB led to a median reduction of 25(OH)D by -22.6% (range -54.5% to -19.5%) between t1 and t2. Cohen's kappa (κ) for method agreement for vitamin D deficiency (tested cut-off values 20 ng/ml and 12 ng/ml), was κ = 0.291 (p < 0.001) and κ = 0.469 (p < 0.001), respectively. The mean difference between measurements by ECLIA and LC-MS/MS was 4.8 ng/ml (±5.7), Pearson's r for correlation was 0.73 (p < 0.001). The biologically inactive C3-epimer did not contribute to 25(OH)D levels assessed by LC-MS/MS.ConclusionThe 25(OH)D measurements by chemiluminescence assays can noticeably deviate from those measured by LC-MS/MS, which can be considered the unequivocal gold standard. These assays may still be acceptably reliable in the screening for vitamin D deficiency, especially in the setting of low vitamin D levels. Stricter definitions, e.g. serum 25(OH)D levels lower than 12 ng/ml, may be used to diagnose deficiency with low false positive rate.Trial RegistrationDRKS00009216, German Clinical Trials Registry ( www.drks.de ).

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