title: Performance characteristics between TDx®FLx and TBA™-25FR for the therapeutic drug monitoring of methotrexate.
abstract: BACKGROUND
  High-dose methotrexate (HDMTX) is used in the treatment of certain malignancies, including leptomeningeal metastases, systemic non-Hodgkin lymphoma, acute lymphoblastic leukemia, and osteosarcoma. High circulating levels of methotrexate can cause severe myelosuppression. The present study aimed to examine the differences in plasma MTX concentrations measured by two immunoassay systems currently available in the Japanese market, a TDX/FLX analyzer and a TBA-25FR analyzer.
  
  
  METHODS
  A total of 69 plasma samples from 16 patients were assayed by a fluorescence polarization immunoassay technique using a TDx/FLx analyzer (Abbott Diagnostics, Chicago, Illinois, U.S.A.) and a homogeneous enzyme immunoassay technique using a TBA-25FR analyzer (Toshiba Medical Systems, Tokyo, Japan).
  
  
  RESULTS
  Assay results were very consistent between the two systems, with good correlation 24 h after the start of treatment (TBA-25FR = 1.06・TDX/FLX, -1.31, r = 0.99), 48 h after the start of treatment (TBA-25FR = 1.00・TDX/FLX, +0.027, r > 0.99), and 72 h after the start of treatment (TBA-25FR = 1.09・TDX/FLX, +0.011, r > 0.99).
  
  
  CONCLUSIONS
  The calibration curve spanned one order of magnitude with a linear working range from the lowest to the highest standard. The standard deviations show the excellent reproducibility of repeated measurements at each standard level for both immunoassay systems. However, when using the TBA-25FR, it is necessary to perform measurements in the low-concentration range with care.
authors.affiliation: Department of Clinical Pharmacy, Oita University Hospital, Hasama-machi, Oita 879-5593 Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kaneko
authors.affiliation: Department of Clinical Pharmacy, Oita University Hospital, Hasama-machi, Oita 879-5593 Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Fujioka
authors.affiliation: Department of Clinical Pharmacy, Oita University Hospital, Hasama-machi, Oita 879-5593 Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Department of Clinical Pharmacy, Oita University Hospital, Hasama-machi, Oita 879-5593 Japan.
authors.forename: Yuhki
authors.initials: Y
authors.lastname: Sato
authors.affiliation: Department of Clinical Pharmacy, Oita University Hospital, Hasama-machi, Oita 879-5593 Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Itoh
keywords: Automatic immunoassay systems; High-dose Methotrexate; Methotrexate; Therapeutic drug monitoring