Test ID: HCYSP
Homocysteine, Total, Plasma
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
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 (MAT) I/III deficiency
Method Name A short description of the method used to perform the test
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
Aliases Lists additional common names for a test, as an aid in searching
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: Lavender top (EDTA) or plasma gel (EDTA)
Specimen Volume: 0.4 mL
Collection Instructions:
1. Fasting (12 hours, preferred but not required)
2. Immediately place specimen on wet ice.
3. Spin down and separate plasma from cells within 4 hours of draw.
4. Alternatively, if blood is not immediately placed on ice, plasma must be removed from cells within 1 hour of draw.
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 OK |
| Lipemia | Mild OK; Gross OK |
| Icterus | Mild OK; Gross OK |
| Other | NA |
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 |
|---|---|---|
| Plasma EDTA | Refrigerated (preferred) | |
| Frozen | ||
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. Genetic defects in vitamin cofactors (vitamin B6, B12, and folate) and nutritional deficiency of B12 and folate also lead to abnormal homocysteine accumulation.
Homocysteine concentration is an indicator of acquired folate or cobalamin deficiency, and is a contributing factor in the pathogenesis of neural tube defects. 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: < or =13 mcmol/L
Reference values apply to fasting specimens only.
Interpretation Provides information to assist in interpretation of the test results
Homocysteine concentrations >13 mcmol/L are considered abnormal in patients evaluated for suspected nutritional deficiencies (B12, folate) and inborn errors of metabolism. Measurement of methylmalonic acid (MMA) distinguishes between B12 (cobalamin) and folate deficiencies, as MMA is only elevated in B12 deficiency. Response to dietary treatment can be evaluated by monitoring plasma homocysteine concentrations over time.
Homocysteine concentrations < or =10 mcmol/L are desirable when utilized for cardiovascular risk.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
A fasting specimen is recommended; however, nonfasting homocysteine concentrations produce slightly higher, but likely clinically insignificant changes.
Other factors that may influence and increase plasma homocysteine include:
-Age
-Smoking
-Poor diet/cofactor deficiencies
-Chronic kidney disease/renal disease
-Hypothyroidism
Medications that may increase homocysteine concentrations include:
| Medication | Effect |
| Methotrexate | 5-Methyltetrahydrofolate depletion |
| Azuridine | Vitamin B6 antagonist |
| Nitrous Oxide | Inactivation of methionine synthase |
| Phenytoin | Interference with folate metabolism |
| Carbamazepine | Interference with folate metabolism |
| Oral Contraceptives | Estrogen-induced vitamin B6 deficiency |
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. Myers GL, Christenson RH, Cushman M, et al: National Academy of Clinical Biochemistry Laboratory Medicine Practice guidelines: emerging biomarkers for primary prevention of cardiovascular disease. Clin Chem, 2009;55(2):51-57
3. Refsum H, Smith AD, Ueland PM, et al: Facts and recommendations about total homocysteine determinations: an expert opinion. Clin Chem 2004 January;50:3-32
4. Turgeon CT, Magera MJ, Cuthbert CD, et al: Determination of total homocysteine, methylmalonic acid, and 2-methylcitric acid in dried blood spots by tandem mass spectrometry. Clin Chem 2010 November;56:1686-1695
Method Description Describes how the test is performed and provides a method-specific reference
One hundred microL of plasma are spiked with d(8)-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; 2 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.
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.
83090
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 |
|---|---|---|
| 80379 | Homocysteine, Total, P | 13965-9 |
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