title: Bioassay for detection of methotrexate in serum.
abstract: OBJECTIVE
  A bioassay is developed for the measurement of methotrexate (MTX) in serum.
  
  
  METHODS
  The assay is based on MTX inhibition of the proliferation of hypoxanthine-guanosine phosphoribosyl transferase (HGPRT) negative mouse B-cells (B9.H). HGPRT negative cells cannot use the salvage pathway of nucleotide synthesis to overcome inhibition by MTX.
  
  
  RESULTS
  When B9.H cells are cultured with serial dilutions of serum, inhibition of proliferation is a measure of the amount of MTX in the serum. Circulating folates do not interfere with the assay.
  
  
  CONCLUSIONS
  This simple assay can detect low concentrations of MTX in serum: it is therefore useful for following the pharmacodynamics of functional MTX after low-dose MTX treatment.
authors.affiliation: Sanquin Research at CLB, and Landsteiner Laboratory, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: de Lathouder
authors.forename: A H
authors.initials: AH
authors.lastname: Gerards
authors.forename: E R
authors.initials: ER
authors.lastname: de Groot
authors.forename: M G
authors.initials: MG
authors.lastname: Valkhof
authors.forename: B A C
authors.initials: BA
authors.lastname: Dijkmans
authors.forename: L A
authors.initials: LA
authors.lastname: Aarden
mesh_terms: D000818:Animals; D018501:Antirheumatic Agents / Q000008:administration & dosage / Q000097:blood*; D001402:B-Lymphocytes; D001681:Biological Assay / Q000379:methods; D018929:Cell Culture Techniques; D002455:Cell Division; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000096:biosynthesis*; D008727:Methotrexate / Q000008:administration & dosage / Q000097:blood*; D051379:Mice; D012680:Sensitivity and Specificity
chemical_list: D018501:Antirheumatic Agents; D007041:Hypoxanthine Phosphoribosyltransferase; D008727:Methotrexate