Test ID: MTX
Methotrexate, Serum
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Following therapy, serum concentration is used to judge whether the drug is being cleared appropriately and verify that a nontoxic level has been attained.
Method Name A short description of the method used to perform the test
Immunoassay
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Collection Container/Tube: Red top
Submission Container/Tube: Amber vial (Supply T192)
Specimen Volume: 1 mL
Collection Instructions: Send specimen in amber vial to protect from light.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | Mild OK; Gross reject |
| Icterus | Mild OK; Gross reject |
| Other | Serum gel tube |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum Red | Frozen (preferred) | 14 days |
| Refrigerated | 7 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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.
When used as an antineoplastic agent against these tumors, it 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.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Nontoxic drug concentration after 72 hours: <0.1 mcmol/L
Interpretation Provides information to assist in interpretation of the test results
Following a 4 to 6 hour intravenous infusion of methotrexate, postinfusion concentrations greater than the following indicate an increased risk of toxicity if conventional low dose leucovorin rescue is given:
-24-hour postinfusion concentration: 5.0 to 10.0 mcmol/L
-48-hour postinfusion concentration: 0.5 to 1.0 mcmol/L
-72-hour postinfusion concentration: 0.1 mcmol/L
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
The specimen must be protected from light.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
Cadman EC, Durivage HJ: Cancer chemotherapy: alkylating agents. In Harrison's Principles of Internal Medicine. 12th edition. Edited by JD Wilson, E Braunwald, KJ Isselbacher, et al. New York, McGraw-Hill Book Company, 1991, pp 1592-1594
Method Description Describes how the test is performed and provides a method-specific reference
Enzyme-multiplied immunoassay technique (EMIT) is performed Using Olympus analyzer. EMIT offers an alternative to the traditional spectroscopic and chromatographic method for quantitating blood concentrations of drugs. The technique for drugs is based upon an enzymatic assay for glucose-6-phosphate dehydrogenase, using spectral properties at 340 nm, in which the reduction of nicotinamide adenine dinucleotide (NAD) substrate is monitored. The basis of the drug detection technique is an immunological reaction between the drug and a specific antibody. The reagent contains the enzyme (glucose-6-phosphate dehydrogenase) to which the drug is covalently bound and antibody-specific to the drug. The antibody binds most of the drug-bound enzyme, rendering the enzyme inactive. This results in a baseline enzymatic activity. In the presence of free drug, antibody equilibrates between free drug and enzyme-bound drug leaving some of the drug-bound enzyme uncomplexed and able to catalyze the reaction. If more free drug is introduced, either as standard or sample, then competition for the antibody takes place between the drug in the sample and the drug attached to the enzyme. This results in more drug-bound enzyme being left uncomplexed and able to catalyze the enzyme reaction at a greater rate as compared to the baseline activity. The observed enzyme activity increases with the amount of total free drug in the sample. Methotrexate may also be analyzed by fluorescence polarization immunoassay.(Moyer TP: Therapeutic drug monitoring. In Tietz Textbook of Clinical Chemistry. Fourth edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 2005, pp 1237-1285)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Varies
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
83520
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 8721 | Methotrexate, S | 14836-1 |
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