A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # |
Methotrexate
Test CodeCPT Codes
80299
Preferred Specimen
SST; Red
Minimum Volume
Other Acceptable Specimens
Instructions
Protect specimen from light using a brown paper sack, aluminum foil, or a dark-colored specimen tube.
Transport Container
Serum (gold top) tube or Lithium Heparin Plasma (green top) tube
Transport Temperature
Specimen Stability
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Methodology
Turbidimetric
Setup Schedule
Daily upon receipt
Report Available
Limitations
Reference Range
A serum methotrexate concentration above 5 umol/L (5 x 10-6 mol/L) at 24 hours after high-dose therapy generally indicates a risk of toxicity. This maximum level is provided only as a guide; individual patient results should be interpreted in light of all clinical signs and symptoms.
Clinical Significance
Methotrexate is an antineoplastic agent that inhibits the enzyme dihydrofolate reductase. Such inhibition causes a stoppage of synthesis of tetrahydrofolate that, in turn, results in an inhibition of nucleotide and ultimately of DNA synthesis.
Methotrexate is effective against malignancies with rapid cell proliferation such as acute lymphoblastic leukemia, choriocarcinoma, trophoblastic tumors in women, and carcinomas of the breast, tongue, pharynx, and testis. It can also be used in the treatment of rheumatoid arthritis.
When used as an antineoplastic agent against these tumors, methotrexate is administered at high dose (2.5 mg/kg or 3.3 mg/kg), and usually is followed by leucovorin (folinic acid) rescue to salvage nontumor cells.