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Department

Biochemistry

Preferred Sample Type

Methotrexate (MTX)

Suitable Specimen Types

  • Serum
2 mL serum

Specimen Transport

Inform laboratory before taking sample. Transport to laboratory ASAP

Sample Processing in Laboratory

Please transfer samples to BHH as soon as possible to enable early morning transport to QE. Please contact BHH Biochem lab by bleeping the Duty Biochemist on 2506 to let them know a sample is coming.

Sample Preparation

Centrifuge

Turnaround Time

24 hrs

Sample Stability

4 ºC

Methotrexate (MTX)

General Information

Methotrexate (MTX, formerly known as amethopterin) is an antimetabolite and antifolate drug. In high doses, MTX is used to treat choriocarcinoma, leukemia in the spinal fluid, osteosarcoma, breast cancer, lung cancer, non-Hodgkin lymphoma and head and neck cancers. In these patients, careful monitoring of MTX is required. High dose MTX patients should be monitored at 24hr, 48hr and 72hr post infusion until levels fall to <0.01. results  are needed same day to assess need for rescue  preparation when levels remain high over a longe period p. MTX may also be used, in much lower doses and most commonly is a GP setting, to treat rheumatoid arthritis, psoriasis and other autoimmune disorders. The doses in these patients are small, therefore have concentrations less than the limit of detection of the laboratory assay. Thus in these patients monitor MTX toxicity by measurement of amino transferases or Pro-collagen peptide Type 3 (P3NP).

Patient Preparation

Patient should have been given high dose methotrexate.

Low dose methotrexate - monitoring not required.

Notes

Requesters MUST contact BHH Biochem lab by bleeping the Duty Biochemist on 2506 to let them know a sample is coming and the time after infusion to assist with requirements for dilutions. Samples need to leave BHH on scheduled transport for QE early in the morning, which can be managed so long as staff are aware of the presence of a MTX sample. A Protocol has been drawn up for Haem wards in order to help all staff comply. Please be aware of it when making a request. Your help in this matter is appreciated.

Plain plastic (i.e. Red-topped) tubes are preferable.

Reference Range

Times given are from time 0 (time of starting intravenous methotrexate infusion).

The following samples are required for patient's safe rescue with folinic acid:

48 hours, 72 hours, and then every 24 hours until methotrexate level is less than 0.1 µmol/L.

 

Source of Reference Range

UKALL14 Protocol v5.0 appendix 15

Specifications

  • EQA Scheme?: Yes
  • EQA Status: UK NEQAS (Tox&TDM)