Test Id : PSYR
Psychosine, Whole Blood
Useful For
Suggests clinical disorders or settings where the test may be helpful
Aiding in the biochemical diagnosis of Krabbe disease using whole blood specimens
Follow-up of individuals affected with Krabbe disease
Follow-up testing after an abnormal newborn screening result for Krabbe disease
Monitoring of individuals at risk to develop late onset Krabbe disease
Monitoring of individuals with Krabbe disease after hematopoietic stem cell transplantation
Genetics Test Information
Provides information that may help with selection of the correct genetic test or proper submission of the test request
Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive lysosomal disorder caused by deficient activity of the enzyme galactocerebrosidase.
Krabbe disease is clinically variable; infantile-onset Krabbe disease is the most severe type, with rapid neurological regression resulting in early death.
Highlights
Elevations in psychosine support a diagnosis of Krabbe disease; therefore, psychosine quantitation is a useful biomarker in determining if an individual has active disease. In addition, psychosine quantitation in red blood cells may be a valuable biomarker to monitor disease progression or treatment response in individuals of all ages.
Psychosine may also be elevated in saposin A cofactor deficiency, which results in a similar clinical phenotype to Krabbe disease, but patients typically have normal galactocerebrosidase activity in vitro.
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
If the patient has abnormal newborn screening result for Krabbe disease, immediate action should be taken. Refer to the appropriate American College of Medical Genetics and Genomics Newborn Screening ACT Sheet.(1,2)
Method Name
A short description of the method used to perform the test
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
Galactopsychosine
Galactosylphingosine
Krabbe disease
Psychosine
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
If the patient has abnormal newborn screening result for Krabbe disease, immediate action should be taken. Refer to the appropriate American College of Medical Genetics and Genomics Newborn Screening ACT Sheet.(1,2)
Specimen Type
Describes the specimen type validated for testing
Whole blood
Ordering Guidance
This test is recommended for individuals of all ages, infancy through adulthood, for diagnosis or long-term monitoring of patients who have been treated or who are at risk of developing Krabbe disease.
If a result is needed within 24 hours, order PSY / Psychosine, Blood Spot.
Shipping Instructions
Must be sent refrigerated.
Necessary Information
1. Patient’s age is required.
2. Date of hematopoietic stem cell transplantation (HSCT), if performed.
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Green top (sodium heparin, lithium heparin)
Specimen Volume: 2 mL
Forms
If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
0.5 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole blood | Refrigerated | 7 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Aiding in the biochemical diagnosis of Krabbe disease using whole blood specimens
Follow-up of individuals affected with Krabbe disease
Follow-up testing after an abnormal newborn screening result for Krabbe disease
Monitoring of individuals at risk to develop late onset Krabbe disease
Monitoring of individuals with Krabbe disease after hematopoietic stem cell transplantation
Genetics Test Information
Provides information that may help with selection of the correct genetic test or proper submission of the test request
Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive lysosomal disorder caused by deficient activity of the enzyme galactocerebrosidase.
Krabbe disease is clinically variable; infantile-onset Krabbe disease is the most severe type, with rapid neurological regression resulting in early death.
Testing Algorithm
Delineates situations when tests are added to the initial order. This includes reflex and additional tests.
If the patient has abnormal newborn screening result for Krabbe disease, immediate action should be taken. Refer to the appropriate American College of Medical Genetics and Genomics Newborn Screening ACT Sheet.(1,2)
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive lysosomal disorder caused by deficient activity of the enzyme galactocerebrosidase (GALC). GALC facilitates the lysosomal degradation of psychosine (galactosylsphingosine) and 3 other substrates, galactosylceramide, lactosylceramide, and lactosylsphingosine. Krabbe disease is caused by variants in the GALC gene, and it has an estimated frequency of 1 in 250,000 births.
The clinical course of Krabbe disease can be variable, even within the same family. Eighty-five percent to 90% of patients present before the first year of life with central nervous system impairment, including increasing irritability, developmental delay, and sensitivity to stimuli. Rapid neurodegeneration, including white matter disease follows, with death usually occurring by 2 years of age. Late onset forms of the disease affect 10% to15% of individuals and are characterized by ataxia, vision loss, weakness, and psychomotor regression, typically presenting from age 6 months to the seventh decade of life.
Newborn screening for Krabbe disease has been implemented in some states. The early (presymptomatic) identification and subsequent testing of infants at risk for Krabbe disease may be helpful in reducing the morbidity and mortality associated with this disease. While treatment is mostly supportive, hematopoietic stem cell transplantation has shown some success if performed prior to onset of neurologic damage.
Psychosine is 1 of 4 substrates degraded by GALC and is a neurotoxin at elevated concentrations. It has been shown to be elevated in patients with active Krabbe disease or with saposin A cofactor deficiency and, therefore, may be a useful biomarker for the presence of disease or disease progression.
Reduced or absent GALC in leukocytes (GALCW / Galactocerebrosidase, Leukocytes) or dried blood spots (PLSD / Lysosomal and Peroxisomal Disorders Screen, Blood Spot) along with elevated psychosine levels can indicate a diagnosis of Krabbe disease. Molecular sequencing of the GALC gene (KRABZ / Krabbe Disease, Full Gene Analysis and Large [30 kb] Deletion, Varies) allows for detection of the disease-causing variants in affected patients and carrier detection in family members.
Individuals with a disease phenotype similar to Krabbe disease may have saposin A cofactor deficiency. Saposin A cofactor deficiency also results in elevated psychosine levels. Testing for this condition via molecular analysis of PSAP is useful in those with elevated psychosine and normal to moderately reduced GALC activity with normal molecular genetic GALC sequencing.
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.
Normal <5 pmol/g Hb
Interpretation
Provides information to assist in interpretation of the test results
An elevation of psychosine is indicative of Krabbe disease or saposin A cofactor deficiency.
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Individuals with later onset disease, such as adult-onset Krabbe disease, may have a normal psychosine result.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. Newborn Screening ACT Sheet [Decreased galactocerebrosidase, elevated psychosine] Krabbe Disease (infantile form). American College of Medical Genetics and Genomics; 2021. Updated May 2022. Accessed June 10, 2024. Available at www.acmg.net/PDFLibrary/Krabbe-Infantile.pdf
2. Newborn Screening ACT Sheet [Decreased galactocerebrosidase, mildly elevated psychosine] Krabbe Disease (late-onset form). American College of Medical Genetics and Genomics; 2021. Updated May 2022. Accessed June 10, 2024. Available www.acmg.net/PDFLibrary/Krabbe-Later-Onset.pdf
3. Kwon JM, Matern D, Kurtzberg J, et al. Consensus guidelines for newborn screening, diagnosis and treatment of infantile Krabbe disease. Orphanet J Rare Dis. 2018;13(1):30. doi:10.1186/s13023-018-0766-x
4. Orsini JJ, Escolar ML, Wasserstein MP, et al. Krabbe disease. In: Adam MP, Mirzaa GM, Pagon R, eds. GeneReviews [Interntet]. University of Washington, Seattle; 2000. Updated October 11, 2018. Accessed August 31, 2023. Available at www.ncbi.nlm.nih.gov/books/NBK1238/
5. Turgeon CT, Orsini JJ, Sanders KA, et al. Measurement of psychosine in dried blood spots-a possible improvement to newborn screening programs for Krabbe disease. J Inherit Metab Dis. 2015;38(5):923-929
6. Wenger DA, Escolar ML, Luzi P, Rafi MA. Krabbe disease (globoid cell leukodystrophy). In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed August 31, 2023. Available at https://ommbid.mhmedical.com/content.aspx?sectionid=225546481&bookid=2709
7. Guenzel AJ, Turgeon CT, Nickander KK, et al. The critical role of psychosine in screening, diagnosis, and monitoring of Krabbe disease. Genet Med. 2020;22(6):1108-1118. doi:10.1038/s41436-020-0764-y
8. Thompson-Stone R, Ream MA, Gelb M, et al. Consensus recommendations for the classification and long-term follow up of infants who screen positive for Krabbe disease. Mol Genet Metab. 2021;134(1-2):53-59. doi:10.1016/j.ymgme.2021.03.016
Method Description
Describes how the test is performed and provides a method-specific reference
Psychosine is extracted from washed red blood cells and quantified using an isotopically labeled internal standard by liquid chromatography tandem mass spectrometry.(Unpublished Mayo method)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Tuesday, Thursday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
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
Indicates the location of the laboratory that performs the test
Fees :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
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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 instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US 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 Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
82542
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| PSYR | Psychosine, RBC | 93687-2 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 606152 | Interpretation (PSYR) | 59462-2 |
| 606145 | Psychosine, RBC | 93687-2 |
| 606151 | Reviewed By | 18771-6 |