2011 年 37 巻 5 号 p. 311-315
High-dose methotrexate (MTX) therapy is used to treat cancers such as acute leukemia, malignant lymphoma, and osteosarcoma. Serum MTX levels are usually measured in order to prevent adverse effects and make a schedule for leucovorin rescue in this therapy. TDx® analyzer (TDx®, Abbott), the device currently used for measurement, provides dependable serum MTX measurements. However, the Viva-ETM system (Viva-ETM, Siemens) which has recently started to be used for analysis cannot determine levels <0.30 μmol/L. Since this makes serum MTX levels 72 h after MTX administration uncertain, we investigated methods of improving the detection limit of serum MTX levels with Viva-ETM, and evaluated the validity of its clinical application.
The sample volume was increased from 3.0 to 9.0 μL to detect lower concentrations, and accuracy as well as intra- and interassay variability were evaluated. We also examined a correlation with TDx® measurements for low levels (< 0.30 μmol/L) in samples obtained 48 h and 72 h after MTX administration.
A level of 0.04 μmol/L could be detected,making it possible to monitor serum MTX levels 72 h after MTX administration. The accuracy ( p = 0.78), intra-assay variability (coefficient of variation [C.V.], 1.8-15.1%), inter-assay variability (C.V., 1.48.6%) and correlation with TDx® (y = 1.11x + 0.01, r = 0.97) were reasonable for the clinical setting.
In conclusion, these findings provide useful information for institutions where serum MTX levels are measured using Viva-ETM in patients receiving MTX treatment.