Background: Vitamin D is important to health and disease. Liquid chromatography-tandem mass spectrometry (LC-MSMS) is considered the most accurate technology for quantification of serum 25-hydroxyvitamin D (25OHD) which is the best biomarker for estimating vitamin D nutritional status. Methods: Serum was mixed with acetonitrile containing hexadeuterated 25-hydroxyvitamin D 3 (d 6 -25OHD3) and centrifuged 10 min at 15,634=g. The supernatant was injected onto a turbulent flow preparatory column then transferred to a polar endcapped C18 analytical column. The mass spectrometer was set for positive atmospheric pressure chemical ionization. Results:The analytical cycle time was 5.5 min. Interand intra-assay CV for both analytes across three concentrations ranged from 3.8% to 14.2%. The method was linear from 3.0 to 283.6 nmol/L for 25-hydroxyvitamin D 3 (25OHD3) and 4.6 to 277.9 nmol/L for 25-hydroxyvitamin D 2 (25OHD2), with an accuracy of 88.7%-118.7% and 90.7%-100.3%, respectively. No carryover or ion suppression was observed. Comparison with a radioimmunoassay using patient specimens (ns527) showed a mean difference of 5.

The LC-MS/MS method coupled with turbulent flow technology is rapid and efficient in TDM of whole blood sirolimus.

This simple method for urine metanephrines is suitable for clinical use.