The request form must state the time interval since the last dose.
Therapeutic interval is dependent on the protocol used.
Uncertainty of Measurement:
0.02 umol/L at a concentration of 0.07 umol/L
9% at concentrations of 0.4 to 5.0 umol/L
20% at concentrations of 50 umol/L
Principle: Colourimetric
Reagents: ARK Diagnostic INC Methotrexate supplied by Roche
Analyser: Cobas c502
Methotrexate (MTX) therapeutic drug monitoring (TDM) in the oncology setting, with bloods taken at 24 to 72hrs post high dose intravenous MTX infusion to assist leucovorin rescue titration, is quite well established.
In contrast, in the setting of low dose oral MTX regime for e.g. rheumatoid arthritis, psoriasis or inflammatory bowel diseases, MTX level has not been found to correlate well with disease activity, treatment efficacy or toxicity with its level rapidly drops off within 12-24hrs from intake. MTX TDM for these purposes thus is not recommended. Clinical monitoring on efficacy and toxicity coupled with laboratory investigations e.g. liver enzyme tests and full blood count to look for hepatotoxicity and myelosuppression can be useful. Serum P3NP monitoring for MTX related hepatic fibrosis is available from Waikato Hospital laboratory.
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427
Separate within 2 hours, store and transport refrigerated.