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HelpTest Code MTX Methotrexate
Useful For
Methotrexate is an anti-neoplastic and immunosuppressive agent. Following therapy, methotrexate levels are useful to assess if the drug is being cleared effectively and non-toxic levels are achieved.
Synonyms/Keywords
MTX
Specimen Requirements
| Fasting Required | Specimen Type | Preferred Container/Tube | Acceptable Container/Tube | Specimen Volume | Specimen Minimum Volume (allows for 1 repeat) |
Pediatric Minimum Volume (no repeat) |
|---|---|---|---|---|---|---|
| No | Serum/ Plasma | Red Top Tube(RTT) | Lithium-heparin Plasma Separator (PST) Lithium or Sodium-heparin Green Top (GTT) | 0.5 mL | 0.2 mL | 0.1 mL |
Collection/Processing Instructions
Plasma separator tubes are only acceptable if plasma is removed within one hour of collection.
Wrap the specimen tube in aluminum foil to protect from light and place on cold pack or wet ice immediately after drawing.
Separate serum or plasma from the blood within 60 minutes of collection.
Protect the aliquot after separation from light and keep it refrigerated until analyzed.
Specimen must be free of particulate matter including fibrin.
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum/ Plasma | Refrigerate | ≤ 15 Days |
| Frozen at -20 deg Celsius | 30 days | |
| Frozen at -70 deg Celsius | Longer time |
Rejection Criteria
Sample not protected from light.
Test Information
Methotrexate (MTX) is an antineoplastic and immunosuppressive drug effective against malignancies with rapid cell proliferation such as acute lymphoblastic leukemia and certain carcinomas. It can safely be administered over a wide dose range as chemotherapy and also for the treatment of several nononcologic diseases as rheumatoid arthritis or psoriasis. Moderate to high doses of methotrexate can be favorably administered with leucovorin rescue by closely monitoring MTX serum levels to prevent potentially toxic effects. Accurate measurement of MTX levels at 0.5 mol/L, therefore, enables determination of nontoxic status.
Methotrexate value should be used in conjunction with information available from clinical evaluation and other diagnostic procedures.
Use the same method consistently for individual patient care due to the potential for method-to-method variability.
Interferences
The principal known metabolite of methotrexate, 7-hydroxy-methotrexate, shows cross-reactivity in the assay of less than 1%. 4-amino-4-deoxy-N10-methylpteroic acid.
Interpretations
Following a 4 to 6 hour intravenous infusion of methotrexate, post-infusion concentrations greater than the following indicate an increased risk of toxicity if conventional low dose leucovorin rescue is given:
- 24 hours post-infusion concentrations >10 mol/L
- 48 hours post-infusion concentrations >1.0 mol/L
- 72 hours post-infusion concentrations >0.1 mol/L
Reference Range Information
| Performing Location | Reference Range |
|---|---|
| Marshfield |
Nontoxic drug concentration after 24 hrs: < 10.0 mol/L Nontoxic drug concentration after 48 hrs: < 1.0 mol/L |
Marshfield Labs Performing Department
Marshfield Labs Chemistry
Performing Information
| Performing Location | Day(s) Test Performed | Analytical Time | Methodology/Instrumentation |
|---|---|---|---|
| Marshfield | Monday through Sunday | 2-4 hours | ARK Diagnostic Homogeneous Immunoassay/Beckman AU |
CPT Codes
| CPT | Modifier (if needed) |
Quantity | Description | Comments |
|---|---|---|---|---|
| 80204 | 1 |
Outreach CPT Codes
| CPT | Modifier (if needed) |
Quantity | Description | Comments |
|---|---|---|---|---|
| 80204 | 1 |
Ordering Applications
| Ordering Application | Description |
|---|---|
| Cerner | Methotrexate Level |