ARK™ Methotrexate Assay

The ARK™ Methotrexate Assay is a highly specific homogeneous enzyme immunoassay for the accurate quantitative determination of methotrexate in human serum or plasma. The assay provides reliable results for the monitoring of methotrexate levels even at concentrations as low as 0.05 µmol/L. More importantly, the assay has a very low cross-reactivity to 7-Hydroxymethotrexate, the major metabolite of Methotrexate.

The liquid reagents, calibrators and controls are ready to use directly out of the fridge. Pack sizes have been designed to match the typical workloads in a routine lab. ARK™ Methotrexate reagents, calibrators and controls are CE marked and suitable for all major clinical chemistry analyzers. Applications are available for a number of instruments, including Abbott ARCHITECT®, Beckman Coulter AU Series, Roche Cobas® and Siemens ADVIA®.

Assay Characteristics

  • Very low cross-reactivity to 7-Hydroxymethotrexate (≤ 0.07%)
  • Well suited for the detection of MTx in the low ranges, with a limit of detection at 0.02 µmol/L and a limit of quantification at 0.04 µmol/L.
  • Dilution protocols are available to extend the concentration range up to 1 000 µmol/L
  • Convenient, liquid-stable, ready-to-use format
  • Applications are available for all major automated clinical chemistry analysers
  • Excellent calibration range
  • The calibration curve is stable from 3 days to up to 6 weeks, depending on instrument type and work load
  • Non-hazardous preservatives do not contain sodium azide


Methotrexate inhibits the growth of rapidly reproducing cells, such as cancer, skin or bone marrow cells, by interfering with the folic acid metabolism. As an antimetabolite and antifolate drug, it is used for high-dose therapy in combined anti-cancer drug regimens and the low-dose treatment of severe psoriasis, Morbus Crohn, rheumatoid arthritis and other auto-immune diseases.

Treatment with methotrexate may lead to major toxic effects, such as hepatic, pulmonary, renal and bone marrow abnormalities. These may be life threatening, especially in high dose therapy.

With the ARK™ Methotrexate Assay, Specialty Diagnostix offers a reliable tool for the monitoring of serum methotrexate concentrations, thus helping to reduce toxicity and to optimize patient-specific dose adjustment.