Homocysteine, Total, Urine
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
As an aid for screening patients suspected of having an inherited disorder of methionine metabolism including:
-Cystathionine beta-synthase deficiency (Homocystinuria)
-Methylenetetrahydrofolate reductase deficiency (MTHFR) and its thermolabile variants:
- Methionine synthase deficiency
-Cobalamin (Cbl) Metabolism:
- Combined Methyl-Cbl and Adenosyl-Cbl deficiencies: Cbl C2, Cbl D2 and Cbl F3 deficiencies
- Methyl-Cbl specific deficiencies: Cbl D-Var1, Cbl E and Cbl G deficiencies
-Transcobalamin II deficiency:
- Adenosylhomocysteinase: AHCY deficiency
- Glycine N-methyltransferase: GNMT deficiency
- Methionine Adenosyltransferase I/III Deficiency: MAT I/III deficiency
As a (weak) indicator of cardiovascular risk
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) Stable Isotope Dilution Analysis
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Homocysteine, Total, U
Homocystine(single Amino Acid only)(order 80378/single Homocystine req)
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.
Container/Tube: Plastic, 10-mL urine tube (Supply T068)
Specimen Volume: 4 mL
1. Void and discard the first-morning urine specimen following an overnight fast.
2. Continue fasting, and collect the next random urine specimen.
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.
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
|Urine||Refrigerated (preferred)||7 days|
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
To be used in conjunction with plasma amino acids and urine organic acids to aid in the biochemical screening for primary and secondary disorders of methionine metabolism.
Homocysteine is an intermediary in the sulfur-amino acid metabolism pathways, linking the methionine cycle to the folate cycle. Inborn errors of metabolism that lead to homocysteinemia/-uria include cystathionine beta-synthase deficiency (homocystinuria) and various defects of methionine re-methylation.
Homocysteine also was thought to be an independent predictor of cardiovascular disease (atherosclerosis, heart disease, thromboembolism), as early observational studies prior to 2000 linked homocysteine to cardiovascular risk and morbidity and mortality. However, following FDA-mandated folic acid supplementation in 1998, homocysteine concentrations decreased by approximately 10% without a similar change in cardiovascular or ischemic events. Currently, the use of homocysteine for assessment of cardiovascular risk is uncertain and controversial. Based on several meta-analyses, at present, homocysteine may be regarded as a weak risk factor for coronary heart disease, and there is a lack of direct causal relationship between hyperhomocysteinemia and cardiovascular disease. It is most likely an indicator of poor lifestyle and diet.
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.
Adults: 0-9 mcmol/g creatinine
Hyperhomocysteinuria could be caused by either genetic or nutritional factors. While the highest levels are characteristic of classic homocystinuria, there are no reliable cut-offs to differentiate between genetic or dietary causes of elevated homocysteine (HCY) levels. In our experience, very high HCY levels have been seen in some patients with cystathione beta-synthase deficiency.
HCY levels >9 mcmol/g creatinine are considered abnormal in patients under evaluation for cardiovascular or neurovascular disease.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Response to dietary treatment can be better evaluated by monitoring plasma homocysteine (HCYSP/80379 Homocysteine, Total, Plasma) levels over time.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Mudd SH, Levy HL, Kraus JP: Disorders of transsulfuration. In The Metabolic and Molecular Basis of Inherited Disease. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw Hill Book Company, 2001, pp 2007-2056
2. Klee GG: Cobalamin and folate evaluation: measurement of methylmalonic acid and homocysteine vs vitamin B(12) and folate. Clin Chem 2000;46(B):1277-1283
Method Description Describes how the test is performed and provides a method-specific reference
100 mcL of urine is spiked with d8-homocystine (2 nmoles) added as internal standard. After specimen reduction and deproteinization, the analysis by tandem mass spectrometry is performed in the multiple reaction monitoring mode.(Magera MJ, Lacey JM, Casetta B, Rinaldo P: A method for the determination of total homocysteine in plasma and urine by stable isotope dilution and electrospray tandem mass spectrometry. Clin Chem 1999;45:1517-1522)
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 Friday; 12 p.m.
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.
2 days (not reported Sundays)
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.
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.
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.
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|
|80378||Homocysteine, Total, U||26582-7|